1.
ChemSpider
–
ChemSpider is a database of chemicals. ChemSpider is owned by the Royal Society of Chemistry, the database contains information on more than 50 million molecules from over 500 data sources including, Each chemical is given a unique identifier, which forms part of a corresponding URL. This is an approach to develop an online chemistry database. The search can be used to widen or restrict already found results, structure searching on mobile devices can be done using free apps for iOS and for the Android. The ChemSpider database has been used in combination with text mining as the basis of document markup. The result is a system between chemistry documents and information look-up via ChemSpider into over 150 data sources. ChemSpider was acquired by the Royal Society of Chemistry in May,2009, prior to the acquisition by RSC, ChemSpider was controlled by a private corporation, ChemZoo Inc. The system was first launched in March 2007 in a release form. ChemSpider has expanded the generic support of a database to include support of the Wikipedia chemical structure collection via their WiChempedia implementation. A number of services are available online. SyntheticPages is an interactive database of synthetic chemistry procedures operated by the Royal Society of Chemistry. Users submit synthetic procedures which they have conducted themselves for publication on the site and these procedures may be original works, but they are more often based on literature reactions. Citations to the published procedure are made where appropriate. They are checked by an editor before posting. The pages do not undergo formal peer-review like a journal article. The comments are moderated by scientific editors. The intention is to collect practical experience of how to conduct useful chemical synthesis in the lab, while experimental methods published in an ordinary academic journal are listed formally and concisely, the procedures in ChemSpider SyntheticPages are given with more practical detail. Comments by submitters are included as well, other publications with comparable amounts of detail include Organic Syntheses and Inorganic Syntheses
ChemSpider
–
ChemSpider
2.
DrugBank
–
The DrugBank database is a comprehensive, freely accessible, online database containing information on drugs and drug targets. As both a bioinformatics and a resource, DrugBank combines detailed drug data with comprehensive drug target information. Because of its scope, comprehensive referencing and unusually detailed data descriptions. As a result, links to DrugBank are maintained for nearly all drugs listed in Wikipedia, DrugBank is widely used by the drug industry, medicinal chemists, pharmacists, physicians, students and the general public. Its extensive drug and drug-target data has enabled the discovery and repurposing of a number of existing drugs to treat rare, the latest release of the database contains 8227 drug entries including 2003 FDA-approved small molecule drugs,221 FDA-approved biotech drugs,93 nutraceuticals and over 6000 experimental drugs. Additionally,4270 non-redundant protein sequences are linked to these drug entries, each DrugCard entry contains more than 200 data fields with half of the information being devoted to drug/chemical data and the other half devoted to drug target or protein data. Four additional databases, HMDB, T3DB, SMPDB and FooDB are also part of a suite of metabolomic/cheminformatic databases. The first version of DrugBank was released in 2006 and this early release contained relatively modest information about 841 FDA-approved small molecule drugs and 113 biotech drugs. It also included information on 2133 drug targets, the second version of DrugBank was released in 2009. This greatly expanded and improved version of the database included 1344 approved small molecule drugs and 123 biotech drugs as well as 3037 unique drug targets. Version 2.0 also included, for the first time, withdrawn drugs and illicit drugs, version 3.0 was released in 2011. This version contained 1424 approved small molecule drugs and 132 biotech drugs as well as >4000 unique drug targets, version 3.0 also included drug transporter data, drug pathway data, drug pricing, patent and manufacturing data as well as data on >5000 experimental drugs. Version 4.0 was released in 2014 and this version included 1558 FDA-approved small molecule drugs,155 biotech drugs and 4200 unique drug targets. Version 4.0 also incorporated information on drug metabolites, drug taxonomy, drug spectra, drug binding constants. Table 1 provides a complete statistical summary of the history of DrugBank’s development. All data in DrugBank is non-proprietary or is derived from a non-proprietary source and it is freely accessible and available to anyone. In addition, nearly every item is fully traceable and explicitly referenced to the original source. DrugBank data is available through a web interface and downloads
DrugBank
–
Fig. 1. DrugBank DrugCard
3.
IUPHAR/BPS
–
The IUPHAR/BPS Guide to PHARMACOLOGY is an open-access website, acting as a portal to information on the biological targets of licensed drugs and other small molecules. The Guide to PHARMACOLOGY is developed as a joint venture between the International Union of Basic and Clinical Pharmacology and the British Pharmacological Society and this replaces and expands upon the original 2009 IUPHAR Database. The information featured includes pharmacological data, target and gene nomenclature, overviews and commentaries on each target family are included, with links to key references. The Guide to PHARMACOLOGY was initially made available online in December 2011 with additional material released in July 2012 and its network of over 700 specialist advisors contribute expertise and data. The current PI and Grant holder of the GtoPdb project is Prof. Jamie A. Davies, the development and release of the first version of the GtoPdb in 2012 was described in an editorial published in the British Journal of Pharmacology entitled Guide to Pharmacology. org- an update. The IUPHAR-DB is no longer being developed and all the contained within this site is now available through the Guide to PHARMACOLOGY. A complete list of all the approved drugs included on the website is available via the ligand list. The Guide to PHARMACOLOGY is being expanded to include information on targets and ligands. Search features on the website include quick and advanced search options, other features include Hot topic news items and a recent receptor-ligand pairing list. A hard copy summary of the database is published as The Concise Guide to Pharmacology 2015/2016 as a series of papers as a bi-annual supplement to the British Journal of Pharmacology. The Guide to PHARMACOLOGY includes links to other relevant resources via target, many of these resources maintain reciprocal links with the relevant Guide to PHARMACOLOGY pages. As of November 2015 the Wellcome Trust is supporting a new project to develop the Guide to Immumopharmacology, the latter continues to be supported by the British Pharmacological Society
IUPHAR/BPS
–
IUPHAR/BPS Guide to Pharmacology
4.
PubChem
–
PubChem is a database of chemical molecules and their activities against biological assays. The system is maintained by the National Center for Biotechnology Information, a component of the National Library of Medicine, PubChem can be accessed for free through a web user interface. Millions of compound structures and descriptive datasets can be downloaded via FTP. PubChem contains substance descriptions and small molecules with fewer than 1000 atoms and 1000 bonds, more than 80 database vendors contribute to the growing PubChem database. PubChem consists of three dynamically growing primary databases, as of 28 January 2016, Compounds,82.6 million entries, contains pure and characterized chemical compounds. Substances,198 million entries, contains also mixtures, extracts, complexes, bioAssay, bioactivity results from 1.1 million high-throughput screening programs with several million values. PubChem contains its own online molecule editor with SMILES/SMARTS and InChI support that allows the import and export of all common chemical file formats to search for structures and fragments. In the text search form the database fields can be searched by adding the name in square brackets to the search term. A numeric range is represented by two separated by a colon. The search terms and field names are case-insensitive, parentheses and the logical operators AND, OR, and NOT can be used. AND is assumed if no operator is used, example,0,5000,50,10 -5,5 PubChem was released in 2004. The American Chemical Society has raised concerns about the publicly supported PubChem database and they have a strong interest in the issue since the Chemical Abstracts Service generates a large percentage of the societys revenue. To advocate their position against the PubChem database, ACS has actively lobbied the US Congress, soon after PubChems creation, the American Chemical Society lobbied U. S. Congress to restrict the operation of PubChem, which they asserted competes with their Chemical Abstracts Service
PubChem
–
PubChem
5.
International Chemical Identifier
–
Initially developed by IUPAC and NIST from 2000 to 2005, the format and algorithms are non-proprietary. The continuing development of the standard has supported since 2010 by the not-for-profit InChI Trust. The current version is 1.04 and was released in September 2011, prior to 1.04, the software was freely available under the open source LGPL license, but it now uses a custom license called IUPAC-InChI Trust License. Not all layers have to be provided, for instance, the layer can be omitted if that type of information is not relevant to the particular application. InChIs can thus be seen as akin to a general and extremely formalized version of IUPAC names and they can express more information than the simpler SMILES notation and differ in that every structure has a unique InChI string, which is important in database applications. Information about the 3-dimensional coordinates of atoms is not represented in InChI, the InChI algorithm converts input structural information into a unique InChI identifier in a three-step process, normalization, canonicalization, and serialization. The InChIKey, sometimes referred to as a hashed InChI, is a fixed length condensed digital representation of the InChI that is not human-understandable. The InChIKey specification was released in September 2007 in order to facilitate web searches for chemical compounds and it should be noted that, unlike the InChI, the InChIKey is not unique, though collisions can be calculated to be very rare, they happen. In January 2009 the final 1.02 version of the InChI software was released and this provided a means to generate so called standard InChI, which does not allow for user selectable options in dealing with the stereochemistry and tautomeric layers of the InChI string. The standard InChIKey is then the hashed version of the standard InChI string, the standard InChI will simplify comparison of InChI strings and keys generated by different groups, and subsequently accessed via diverse sources such as databases and web resources. Every InChI starts with the string InChI= followed by the version number and this is followed by the letter S for standard InChIs. The remaining information is structured as a sequence of layers and sub-layers, the layers and sub-layers are separated by the delimiter / and start with a characteristic prefix letter. The six layers with important sublayers are, Main layer Chemical formula and this is the only sublayer that must occur in every InChI. The atoms in the formula are numbered in sequence, this sublayer describes which atoms are connected by bonds to which other ones. Describes how many hydrogen atoms are connected to each of the other atoms, the condensed,27 character standard InChIKey is a hashed version of the full standard InChI, designed to allow for easy web searches of chemical compounds. Most chemical structures on the Web up to 2007 have been represented as GIF files, the full InChI turned out to be too lengthy for easy searching, and therefore the InChIKey was developed. With all databases currently having below 50 million structures, such duplication appears unlikely at present, a recent study more extensively studies the collision rate finding that the experimental collision rate is in agreement with the theoretical expectations. Example, Morphine has the structure shown on the right, as the InChI cannot be reconstructed from the InChIKey, an InChIKey always needs to be linked to the original InChI to get back to the original structure
International Chemical Identifier
–
L -
ascorbic acid
6.
Simplified molecular-input line-entry system
–
The simplified molecular-input line-entry system is a specification in form of a line notation for describing the structure of chemical species using short ASCII strings. SMILES strings can be imported by most molecule editors for conversion back into two-dimensional drawings or three-dimensional models of the molecules, the original SMILES specification was initiated in the 1980s. It has since modified and extended. In 2007, a standard called OpenSMILES was developed in the open-source chemistry community. Other linear notations include the Wiswesser Line Notation, ROSDAL and SLN, the original SMILES specification was initiated by David Weininger at the USEPA Mid-Continent Ecology Division Laboratory in Duluth in the 1980s. The Environmental Protection Agency funded the project to develop SMILES. It has since modified and extended by others, most notably by Daylight Chemical Information Systems. In 2007, a standard called OpenSMILES was developed by the Blue Obelisk open-source chemistry community. Other linear notations include the Wiswesser Line Notation, ROSDAL and SLN, in July 2006, the IUPAC introduced the InChI as a standard for formula representation. SMILES is generally considered to have the advantage of being slightly more human-readable than InChI, the term SMILES refers to a line notation for encoding molecular structures and specific instances should strictly be called SMILES strings. However, the term SMILES is also used to refer to both a single SMILES string and a number of SMILES strings, the exact meaning is usually apparent from the context. The terms canonical and isomeric can lead to confusion when applied to SMILES. The terms describe different attributes of SMILES strings and are not mutually exclusive, typically, a number of equally valid SMILES strings can be written for a molecule. For example, CCO, OCC and CC all specify the structure of ethanol, algorithms have been developed to generate the same SMILES string for a given molecule, of the many possible strings, these algorithms choose only one of them. This SMILES is unique for each structure, although dependent on the algorithm used to generate it. These algorithms first convert the SMILES to a representation of the molecular structure. A common application of canonical SMILES is indexing and ensuring uniqueness of molecules in a database, there is currently no systematic comparison across commercial software to test if such flaws exist in those packages. SMILES notation allows the specification of configuration at tetrahedral centers, and these are structural features that cannot be specified by connectivity alone and SMILES which encode this information are termed isomeric SMILES
Simplified molecular-input line-entry system
–
Generation of SMILES: Break cycles, then write as branches off a main backbone. (Ciprofloxacin)
7.
Chemical formula
–
These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas can fully specify the structure of only the simplest of molecules and chemical substances, the simplest types of chemical formulas are called empirical formulas, which use letters and numbers indicating the numerical proportions of atoms of each type. Molecular formulas indicate the numbers of each type of atom in a molecule. For example, the formula for glucose is CH2O, while its molecular formula is C6H12O6. This is possible if the relevant bonding is easy to show in one dimension, an example is the condensed molecular/chemical formula for ethanol, which is CH3-CH2-OH or CH3CH2OH. For reasons of structural complexity, there is no condensed chemical formula that specifies glucose, chemical formulas may be used in chemical equations to describe chemical reactions and other chemical transformations, such as the dissolving of ionic compounds into solution. A chemical formula identifies each constituent element by its chemical symbol, in empirical formulas, these proportions begin with a key element and then assign numbers of atoms of the other elements in the compound, as ratios to the key element. For molecular compounds, these numbers can all be expressed as whole numbers. For example, the formula of ethanol may be written C2H6O because the molecules of ethanol all contain two carbon atoms, six hydrogen atoms, and one oxygen atom. Some types of compounds, however, cannot be written with entirely whole-number empirical formulas. An example is boron carbide, whose formula of CBn is a variable non-whole number ratio with n ranging from over 4 to more than 6.5. When the chemical compound of the consists of simple molecules. These types of formulas are known as molecular formulas and condensed formulas. A molecular formula enumerates the number of atoms to reflect those in the molecule, so that the formula for glucose is C6H12O6 rather than the glucose empirical formula. However, except for very simple substances, molecular chemical formulas lack needed structural information, for simple molecules, a condensed formula is a type of chemical formula that may fully imply a correct structural formula. For example, ethanol may be represented by the chemical formula CH3CH2OH
Chemical formula
–
Al 2 (SO 4) 3
8.
Odor
–
An odor or odour or fragrance is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. Odors are also commonly called scents, which can refer to both pleasant and unpleasant odors, the terms fragrance and aroma are used primarily by the food and cosmetic industry to describe a pleasant odor, and are sometimes used to refer to perfumes, and to describe floral scent. In contrast, malodor, stench, reek, and stink are used specifically to describe unpleasant odor, the term smell is used for both pleasant and unpleasant odors. In the United Kingdom, odour refers to scents in general, the sense of smell gives rise to the perception of odors, mediated by the olfactory nerve. The olfactory receptor cells are present in the olfactory epithelium. There are millions of olfactory receptor neurons that act as sensory signaling cells, each neuron has cilia in direct contact with air. The olfactory nerve is considered the smell mediator, the axon connects the brain to the external air, odorous molecules act as a chemical stimulus. Molecules bind to receptor proteins extended from cilia, initiating an electric signal, thus, by using a chemical that binds to copper in the mouse nose, so that copper wasn’t available to the receptors, the authors showed that the mice couldnt detect the thiols. However, these also found that MOR244-3 lacks the specific metal ion binding site suggested by Suslick. When the signal reaches a threshold, the fires, sending a signal traveling along the axon to the olfactory bulb. Interpretation of the begins, relating the smell to past experiences. The olfactory bulb acts as a station connecting the nose to the olfactory cortex in the brain. Olfactory information is processed and projected through a pathway to the central nervous system. Odor sensation usually depends on the concentration available to the olfactory receptors, the olfactory system does not interpret a single compound, but instead the whole odorous mix, not necessarily corresponding to concentration or intensity of any single constituent. The widest range of odors consists of compounds, although some simple compounds not containing carbon, such as hydrogen sulfide. The perception of an effect is a two-step process. First, there is the part, the detection of stimuli by receptors in the nose. The stimuli are processed by the region of the brain which is responsible for olfaction
Odor
–
"Smell", from Allegory of the senses by
Jan Brueghel the Elder,
Museo del Prado
Odor
–
Odor control covers at a
sewage treatment plant: Under these covers, grit and gravel are settled out of the wastewater.
9.
Benzene
–
Benzene is an important organic chemical compound with the chemical formula C6H6. The benzene molecule is composed of 6 carbon atoms joined in a ring with 1 hydrogen atom attached to each, because it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon. Benzene is a constituent of crude oil and is one of the elementary petrochemicals. Because of the cyclic continuous pi bond between the atoms, benzene is classed as an aromatic hydrocarbon, the second -annulene. Benzene is a colorless and highly flammable liquid with a sweet smell and it is used primarily as a precursor to the manufacture of chemicals with more complex structure, such as ethylbenzene and cumene, of which billions of kilograms are produced. Because benzene has a high number, it is an important component of gasoline. Because benzene is a carcinogen, most non-industrial applications have been limited. The word benzene derives historically from gum benzoin, a resin known to European pharmacists. An acidic material was derived from benzoin by sublimation, and named flowers of benzoin, the hydrocarbon derived from benzoic acid thus acquired the name benzin, benzol, or benzene. Michael Faraday first isolated and identified benzene in 1825 from the oily residue derived from the production of illuminating gas, in 1833, Eilhard Mitscherlich produced it by distilling benzoic acid and lime. He gave the compound the name benzin, in 1845, Charles Mansfield, working under August Wilhelm von Hofmann, isolated benzene from coal tar. Four years later, Mansfield began the first industrial-scale production of benzene, gradually, the sense developed among chemists that a number of substances were chemically related to benzene, comprising a diverse chemical family. In 1855, Hofmann used the word aromatic to designate this family relationship, in 1997, benzene was detected in deep space. The empirical formula for benzene was known, but its highly polyunsaturated structure. In 1865, the German chemist Friedrich August Kekulé published a paper in French suggesting that the structure contained a ring of six carbon atoms with alternating single and double bonds, the next year he published a much longer paper in German on the same subject. Kekulés symmetrical ring could explain these facts, as well as benzenes 1,1 carbon-hydrogen ratio. Here Kekulé spoke of the creation of the theory and he said that he had discovered the ring shape of the benzene molecule after having a reverie or day-dream of a snake seizing its own tail. This vision, he said, came to him years of studying the nature of carbon-carbon bonds
Benzene
–
A bottle of benzene. The warnings show benzene is a toxic and flammable liquid.
Benzene
–
Geometry of molecule
10.
Density
–
The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume, ρ = m V, where ρ is the density, m is the mass, and V is the volume. In some cases, density is defined as its weight per unit volume. For a pure substance the density has the numerical value as its mass concentration. Different materials usually have different densities, and density may be relevant to buoyancy, purity, osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. Thus a relative density less than one means that the floats in water. The density of a material varies with temperature and pressure and this variation is typically small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object, increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a results in convection of the heat from the bottom to the top. This causes it to rise relative to more dense unheated material, the reciprocal of the density of a substance is occasionally called its specific volume, a term sometimes used in thermodynamics. Density is a property in that increasing the amount of a substance does not increase its density. Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily and compared with the mass, upon this discovery, he leapt from his bath and ran naked through the streets shouting, Eureka. As a result, the term eureka entered common parlance and is used today to indicate a moment of enlightenment, the story first appeared in written form in Vitruvius books of architecture, two centuries after it supposedly took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time, from the equation for density, mass density has units of mass divided by volume. As there are units of mass and volume covering many different magnitudes there are a large number of units for mass density in use. The SI unit of kilogram per metre and the cgs unit of gram per cubic centimetre are probably the most commonly used units for density.1,000 kg/m3 equals 1 g/cm3. In industry, other larger or smaller units of mass and or volume are often more practical, see below for a list of some of the most common units of density
Density
–
Air density vs. temperature
11.
Melting point
–
The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phase exist in equilibrium, the melting point of a substance depends on pressure and is usually specified at standard pressure. When considered as the temperature of the change from liquid to solid. Because of the ability of some substances to supercool, the point is not considered as a characteristic property of a substance. For most substances, melting and freezing points are approximately equal, for example, the melting point and freezing point of mercury is 234.32 kelvins. However, certain substances possess differing solid-liquid transition temperatures, for example, agar melts at 85 °C and solidifies from 31 °C to 40 °C, such direction dependence is known as hysteresis. The melting point of ice at 1 atmosphere of pressure is close to 0 °C. In the presence of nucleating substances the freezing point of water is the same as the melting point, the chemical element with the highest melting point is tungsten, at 3687 K, this property makes tungsten excellent for use as filaments in light bulbs. Many laboratory techniques exist for the determination of melting points, a Kofler bench is a metal strip with a temperature gradient. Any substance can be placed on a section of the strip revealing its thermal behaviour at the temperature at that point, differential scanning calorimetry gives information on melting point together with its enthalpy of fusion. A basic melting point apparatus for the analysis of crystalline solids consists of an oil bath with a transparent window, the several grains of a solid are placed in a thin glass tube and partially immersed in the oil bath. The oil bath is heated and with the aid of the melting of the individual crystals at a certain temperature can be observed. In large/small devices, the sample is placed in a heating block, the measurement can also be made continuously with an operating process. For instance, oil refineries measure the point of diesel fuel online, meaning that the sample is taken from the process. This allows for more frequent measurements as the sample does not have to be manually collected, for refractory materials the extremely high melting point may be determined by heating the material in a black body furnace and measuring the black-body temperature with an optical pyrometer. For the highest melting materials, this may require extrapolation by several hundred degrees, the spectral radiance from an incandescent body is known to be a function of its temperature. An optical pyrometer matches the radiance of a body under study to the radiance of a source that has been previously calibrated as a function of temperature, in this way, the measurement of the absolute magnitude of the intensity of radiation is unnecessary. However, known temperatures must be used to determine the calibration of the pyrometer, for temperatures above the calibration range of the source, an extrapolation technique must be employed
Melting point
–
Melting points (in blue) and boiling points (in pink) of the first eight
carboxylic acids (°C)
Melting point
–
Kofler bench with samples for calibration
Melting point
–
Automatic digital melting point meter
Melting point
–
Pressure dependence of water melting point
12.
Boiling point
–
The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the environmental pressure. A liquid in a vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at high pressure has a boiling point than when that liquid is at atmospheric pressure. For a given pressure, different liquids boil at different temperatures, for example, water boils at 100 °C at sea level, but at 93.4 °C at 2,000 metres altitude. The normal boiling point of a liquid is the case in which the vapor pressure of the liquid equals the defined atmospheric pressure at sea level,1 atmosphere. At that temperature, the pressure of the liquid becomes sufficient to overcome atmospheric pressure. The standard boiling point has been defined by IUPAC since 1982 as the temperature at which boiling occurs under a pressure of 1 bar, the heat of vaporization is the energy required to transform a given quantity of a substance from a liquid into a gas at a given pressure. Liquids may change to a vapor at temperatures below their boiling points through the process of evaporation, evaporation is a surface phenomenon in which molecules located near the liquids edge, not contained by enough liquid pressure on that side, escape into the surroundings as vapor. On the other hand, boiling is a process in which molecules anywhere in the liquid escape, a saturated liquid contains as much thermal energy as it can without boiling. The saturation temperature is the temperature for a corresponding saturation pressure at which a liquid boils into its vapor phase, the liquid can be said to be saturated with thermal energy. Any addition of energy results in a phase transition. If the pressure in a system remains constant, a vapor at saturation temperature will begin to condense into its liquid phase as thermal energy is removed, similarly, a liquid at saturation temperature and pressure will boil into its vapor phase as additional thermal energy is applied. The boiling point corresponds to the temperature at which the pressure of the liquid equals the surrounding environmental pressure. Thus, the point is dependent on the pressure. Boiling points may be published with respect to the NIST, USA standard pressure of 101.325 kPa, at higher elevations, where the atmospheric pressure is much lower, the boiling point is also lower. The boiling point increases with increased pressure up to the critical point, the boiling point cannot be increased beyond the critical point. Likewise, the point decreases with decreasing pressure until the triple point is reached
Boiling point
–
Boiling water
13.
Aqueous solution
–
An aqueous solution is a solution in which the solvent is water. It is usually shown in chemical equations by appending to the relevant chemical formula, for example, a solution of table salt, or sodium chloride, in water would be represented as Na+ + Cl−. The word aqueous means pertaining to, related to, similar to, as water is an excellent solvent and is also naturally abundant, it is a ubiquitous solvent in chemistry. Substances that are hydrophobic often do not dissolve well in water, an example of a hydrophilic substance is sodium chloride. Acids and bases are aqueous solutions, as part of their Arrhenius definitions, the ability of a substance to dissolve in water is determined by whether the substance can match or exceed the strong attractive forces that water molecules generate between themselves. If the substance lacks the ability to dissolve in water the molecules form a precipitate, reactions in aqueous solutions are usually metathesis reactions. Metathesis reactions are another term for double-displacement, that is, when a cation displaces to form a bond with the other anion. The cation bonded with the latter anion will dissociate and bond with the other anion, aqueous solutions that conduct electric current efficiently contain strong electrolytes, while ones that conduct poorly are considered to have weak electrolytes. Those strong electrolytes are substances that are ionized in water. Nonelectrolytes are substances that dissolve in water yet maintain their molecular integrity, examples include sugar, urea, glycerol, and methylsulfonylmethane. When writing the equations of reactions, it is essential to determine the precipitate. To determine the precipitate, one must consult a chart of solubility, soluble compounds are aqueous, while insoluble compounds are the precipitate. Remember that there may not always be a precipitate, when performing calculations regarding the reacting of one or more aqueous solutions, in general one must know the concentration, or molarity, of the aqueous solutions. Solution concentration is given in terms of the form of the prior to it dissolving. Metal ions in aqueous solution Solubility Dissociation Acid-base reaction theories Properties of water Zumdahl S.1997, 4th ed. Boston, Houghton Mifflin Company
Aqueous solution
–
The first
solvation shell of a sodium ion dissolved in water.
14.
Vapor pressure
–
Vapor pressure or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature in a closed system. The equilibrium vapor pressure is an indication of a liquids evaporation rate and it relates to the tendency of particles to escape from the liquid. A substance with a vapor pressure at normal temperatures is often referred to as volatile. The pressure exhibited by vapor present above a surface is known as vapor pressure. As the temperature of a liquid increases, the energy of its molecules also increases. As the kinetic energy of the molecules increases, the number of molecules transitioning into a vapor also increases, the vapor pressure of any substance increases non-linearly with temperature according to the Clausius–Clapeyron relation. The atmospheric pressure boiling point of a liquid is the temperature at which the pressure equals the ambient atmospheric pressure. With any incremental increase in temperature, the vapor pressure becomes sufficient to overcome atmospheric pressure. Bubble formation deeper in the liquid requires a pressure, and therefore higher temperature. More important at shallow depths, is the temperature required to start bubble formation. The surface tension of the wall lead to an overpressure in the very small initial bubbles. Thus, thermometer calibration should not rely on the temperature in boiling water, the vapor pressure that a single component in a mixture contributes to the total pressure in the system is called partial pressure. Vapor pressure is measured in the units of pressure. The International System of Units recognizes pressure as a unit with the dimension of force per area. One pascal is one newton per square meter, experimental measurement of vapor pressure is a simple procedure for common pressures between 1 and 200 kPa. Most accurate results are obtained near the point of substances. Better accuracy is achieved when care is taken to ensure that the entire substance and this is often done, as with the use of an isoteniscope, by submerging the containment area in a liquid bath. Very low vapor pressures of solids can be measured using the Knudsen effusion cell method, the Antoine equation is a mathematical expression of the relation between the vapor pressure and the temperature of pure liquid or solid substances
Vapor pressure
–
Graph of water vapor pressure versus temperature. At the normal boiling point of 100 °C, it equals the standard atmospheric pressure of 760
Torr or 101.325
kPa.
Vapor pressure
–
The picture shows the particle transition, as a result of their vapor pressure, from the liquid phase to the gas phase and converse.
15.
Refractive index
–
In optics, the refractive index or index of refraction n of a material is a dimensionless number that describes how light propagates through that medium. It is defined as n = c v, where c is the speed of light in vacuum, for example, the refractive index of water is 1.333, meaning that light travels 1.333 times faster in a vacuum than it does in water. The refractive index determines how light is bent, or refracted. The refractive indices also determine the amount of light that is reflected when reaching the interface, as well as the angle for total internal reflection. This implies that vacuum has a index of 1. The refractive index varies with the wavelength of light and this is called dispersion and causes the splitting of white light into its constituent colors in prisms and rainbows, and chromatic aberration in lenses. Light propagation in absorbing materials can be described using a refractive index. The imaginary part then handles the attenuation, while the real part accounts for refraction, the concept of refractive index is widely used within the full electromagnetic spectrum, from X-rays to radio waves. It can also be used with wave phenomena such as sound, in this case the speed of sound is used instead of that of light and a reference medium other than vacuum must be chosen. Thomas Young was presumably the person who first used, and invented, at the same time he changed this value of refractive power into a single number, instead of the traditional ratio of two numbers. The ratio had the disadvantage of different appearances, newton, who called it the proportion of the sines of incidence and refraction, wrote it as a ratio of two numbers, like 529 to 396. Hauksbee, who called it the ratio of refraction, wrote it as a ratio with a fixed numerator, hutton wrote it as a ratio with a fixed denominator, like 1.3358 to 1. Young did not use a symbol for the index of refraction, in the next years, others started using different symbols, n, m, and µ. For visible light most transparent media have refractive indices between 1 and 2, a few examples are given in the adjacent table. These values are measured at the yellow doublet D-line of sodium, with a wavelength of 589 nanometers, gases at atmospheric pressure have refractive indices close to 1 because of their low density. Almost all solids and liquids have refractive indices above 1.3, aerogel is a very low density solid that can be produced with refractive index in the range from 1.002 to 1.265. Moissanite lies at the end of the range with a refractive index as high as 2.65. Most plastics have refractive indices in the range from 1.3 to 1.7, for infrared light refractive indices can be considerably higher
Refractive index
–
Thomas Young coined the term index of refraction.
Refractive index
–
A
ray of light being
refracted in a plastic block.
Refractive index
–
Diamonds have a very high refractive index of 2.42.
Refractive index
–
A
split-ring resonator array arranged to produce a negative index of refraction for
microwaves.
16.
Viscosity
–
The viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress. For liquids, it corresponds to the concept of thickness, for example. Viscosity is a property of the fluid which opposes the motion between the two surfaces of the fluid in a fluid that are moving at different velocities. For a given velocity pattern, the stress required is proportional to the fluids viscosity, a fluid that has no resistance to shear stress is known as an ideal or inviscid fluid. Zero viscosity is observed only at low temperatures in superfluids. Otherwise, all fluids have positive viscosity, and are said to be viscous or viscid. A fluid with a high viscosity, such as pitch. The word viscosity is derived from the Latin viscum, meaning mistletoe, the dynamic viscosity of a fluid expresses its resistance to shearing flows, where adjacent layers move parallel to each other with different speeds. It can be defined through the situation known as a Couette flow. This fluid has to be homogeneous in the layer and at different shear stresses, if the speed of the top plate is small enough, the fluid particles will move parallel to it, and their speed will vary linearly from zero at the bottom to u at the top. Each layer of fluid will move faster than the one just below it, in particular, the fluid will apply on the top plate a force in the direction opposite to its motion, and an equal but opposite one to the bottom plate. An external force is required in order to keep the top plate moving at constant speed. The magnitude F of this force is found to be proportional to the u and the area A of each plate. The proportionality factor μ in this formula is the viscosity of the fluid, the ratio u/y is called the rate of shear deformation or shear velocity, and is the derivative of the fluid speed in the direction perpendicular to the plates. Isaac Newton expressed the forces by the differential equation τ = μ ∂ u ∂ y, where τ = F/A. This formula assumes that the flow is moving along parallel lines and this equation can be used where the velocity does not vary linearly with y, such as in fluid flowing through a pipe. Use of the Greek letter mu for the dynamic viscosity is common among mechanical and chemical engineers. However, the Greek letter eta is used by chemists, physicists
Viscosity
–
Pitch has a viscosity approximately 230 billion (2.3 × 10 11) times that of water.
Viscosity
–
Laminar shear of fluid between two plates. Friction between the fluid and the moving boundaries causes the fluid to shear. The force required for this action is a measure of the fluid's viscosity.
Viscosity
–
Example of the viscosity of milk and water. Liquids with higher viscosities make smaller splashes when poured at the same velocity.
Viscosity
–
Honey being drizzled.
17.
Dipole
–
In electromagnetism, there are two kinds of dipoles, An electric dipole is a separation of positive and negative charges. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, a permanent electric dipole is called an electret. A magnetic dipole is a circulation of electric current. A simple example of this is a loop of wire with some constant current through it. Dipoles can be characterized by their moment, a vector quantity. For the current loop, the dipole moment points through the loop. In addition to current loops, the electron, among other fundamental particles, has a dipole moment. That is because it generates a field that is identical to that generated by a very small current loop. However, the magnetic moment is not due to a current loop. It is also possible that the electron has a dipole moment although it has not yet been observed. A permanent magnet, such as a bar magnet, owes its magnetism to the magnetic dipole moment of the electron. The two ends of a bar magnet are referred to as poles, and may be labeled north and south, the dipole moment of the bar magnet points from its magnetic south to its magnetic north pole. The north pole of a bar magnet in a compass points north, however, that means that Earths geomagnetic north pole is the south pole of its dipole moment and vice versa. The only known mechanisms for the creation of magnetic dipoles are by current loops or quantum-mechanical spin since the existence of magnetic monopoles has never been experimentally demonstrated, the term comes from the Greek δίς, twice and πόλος, axis. A physical dipole consists of two equal and opposite point charges, in the sense, two poles. Its field at large distances depends almost entirely on the moment as defined above. A point dipole is the limit obtained by letting the separation tend to 0 while keeping the dipole moment fixed, the field of a point dipole has a particularly simple form, and the order-1 term in the multipole expansion is precisely the point dipole field. Although there are no magnetic monopoles in nature, there are magnetic dipoles in the form of the quantum-mechanical spin associated with particles such as electrons
Dipole
–
The
Earth's magnetic field, approximated as a magnetic dipole. However, the "N" and "S" (north and south) poles are labeled here geographically, which is the opposite of the convention for labeling the poles of a magnetic dipole moment.
18.
Worker safety and health
–
These terms of course also refer to the goals of this field, so their use in the sense of this article was originally an abbreviation of occupational safety and health program/department etc. The goals of occupational safety and health programs include to foster a safe, OSH may also protect co-workers, family members, employers, customers, and many others who might be affected by the workplace environment. In the United States, the occupational health and safety is referred to as occupational health and occupational and non-occupational safety. In common-law jurisdictions, employers have a common law duty to take care of the safety of their employees. As defined by the World Health Organization occupational health deals with all aspects of health, Health has been defined as a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity. Occupational health is a field of healthcare concerned with enabling an individual to undertake their occupation. Health has been defined as It contrasts, for example, with the promotion of health and safety at work, since 1950, the International Labour Organization and the World Health Organization have shared a common definition of occupational health. It was adopted by the Joint ILO/WHO Committee on Occupational Health at its first session in 1950, the concept of working culture is intended in this context to mean a reflection of the essential value systems adopted by the undertaking concerned. Such a culture is reflected in practice in the systems, personnel policy, principles for participation, training policies. Professionals advise on a range of occupational health matters. The research and regulation of safety and health are a relatively recent phenomenon. As labor movements arose in response to concerns in the wake of the industrial revolution. The initial remit of the Inspectorate was to police restrictions on the hours in the textile industry of children. The commission sparked public outrage resulted in the Mines Act of 1842. Otto von Bismarck inaugurated the first social insurance legislation in 1883, similar acts followed in other countries, partly in response to labor unrest. Although work provides many economic and other benefits, an array of workplace hazards also present risks to the health. Personal protective equipment can protect against many of these hazards. Physical hazards affect many people in the workplace, Falls are also a common cause of occupational injuries and fatalities, especially in construction, extraction, transportation, healthcare, and building cleaning and maintenance
Worker safety and health
–
This painting depicts a woman examining her work on a lathe at a factory in Britain during World War II. Her eyes are not protected. Today, such practice would not be permitted in most industrialized countries that adhere to strong occupational health and safety standards for workers. In many countries, such standards are either weak or nonexistent, or poorly enforced.
Worker safety and health
–
Workers cutting marble without any protective gear, Indore, India
Worker safety and health
–
Harry McShane, age 16, 1908. Pulled into machinery in a factory in
Cincinnati and had his arm ripped off at the shoulder and his leg broken without any compensation.
Worker safety and health
–
Workplace safety notices at the entrance of a Chinese construction site.
19.
Safety data sheet
–
A safety data sheet, material safety data sheet, or product safety data sheet is an important component of product stewardship, occupational safety and health, and spill-handling procedures. SDS formats can vary from source to source within a country depending on national requirements, SDSs are a widely used system for cataloging information on chemicals, chemical compounds, and chemical mixtures. SDS information may include instructions for the use and potential hazards associated with a particular material or product. The SDS should be available for reference in the area where the chemicals are being stored or in use, there is also a duty to properly label substances on the basis of physico-chemical, health and/or environmental risk. Labels can include hazard symbols such as the European Union standard symbols, a SDS for a substance is not primarily intended for use by the general consumer, focusing instead on the hazards of working with the material in an occupational setting. It is important to use an SDS specific to country and supplier, as the same product can have different formulations in different countries. The formulation and hazard of a product using a name may vary between manufacturers in the same country. Safety data sheets have made an integral part of the system of Regulation No 1907/2006. The SDS must be supplied in a language of the Member State where the substance or mixture is placed on the market. The 16 sections are, SECTION1, Identification of the substance/mixture, relevant identified uses of the substance or mixture and uses advised against 1.3. Details of the supplier of the safety data sheet 1.4, Emergency telephone number SECTION2, Hazards identification 2.1. Classification of the substance or mixture 2.2, Other hazards SECTION3, Composition/information on ingredients 3.1. Mixtures SECTION4, First aid measures 4.1, Description of first aid measures 4.2. Most important symptoms and effects, both acute and delayed 4.3, indication of any immediate medical attention and special treatment needed SECTION5, Firefighting measures 5.1. Special hazards arising from the substance or mixture 5.3, advice for firefighters SECTION6, Accidental release measure 6.1. Personal precautions, protective equipment and emergency procedures 6.2, methods and material for containment and cleaning up 6.4. Reference to other sections SECTION7, Handling and storage 7.1, conditions for safe storage, including any incompatibilities 7.3. Specific end use SECTION8, Exposure controls/personal protection 8.1, Exposure controls SECTION9, Physical and chemical properties 9.1
Safety data sheet
–
An example SDS in a US format provides guidance for handling a
hazardous substance and information on its composition and properties.
Safety data sheet
–
General topics
20.
GHS hazard pictograms
–
Hazard pictograms form part of the international Globally Harmonized System of Classification and Labelling of Chemicals. Two sets of pictograms are included within the GHS, one for the labelling of containers and for workplace hazard warnings, either one or the other is chosen, depending on the target audience, but the two are not used together. The two sets of use the same symbols for the same hazards, although certain symbols are not required for transport pictograms. Transport pictograms come in variety of colors and may contain additional information such as a subcategory number. It has still to be implemented by the European Union in 2009, the following pictograms are included in the Worldwide Model Using but have not been incorporated into the GHS, ICZ and Catwallsh Hazcom Labelling because of the nature of the hazards. Globally Harmonized System of Classification and Labelling of Chemicals, New York and Geneva, United Nations,2007, ISBN 978-92-1-116957-7, ST/SG/AC. 10/30/Rev. Model Regulations, New York and Geneva, United Nations,2007, ISBN 978-92-1-139120-6, manual of Tests and Criteria, New York and Geneva, United Nations,2002, ISBN 92-1-139087-7, ST/SG/AC. 10/11/Rev.4 GHS pictogram gallery from the United Nations Economic Commission for Europe
GHS hazard pictograms
–
Usage
21.
Flash point
–
The flash point is the lowest temperature at which vapours of a volatile material will ignite, when given an ignition source. The flash point may sometimes be confused with the autoignition temperature, the fire point is the lowest temperature at which the vapor will keep burning after being ignited and the ignition source removed. The fire point is higher than the point, because at the flash point the vapor may be reliably expected to cease burning when the ignition source is removed. The flash point is a characteristic that is used to distinguish between flammable liquids, such as petrol, and combustible liquids, such as diesel. It is also used to characterize the fire hazards of liquids, all liquids have a specific vapor pressure, which is a function of that liquids temperature and is subject to Boyles Law. As temperature increases, vapor pressure increases, as vapor pressure increases, the concentration of vapor of a flammable or combustible liquid in the air increases. Hence, temperature determines the concentration of vapor of the liquid in the air. The flash point is the lowest temperature at which there will be enough flammable vapor to induce ignition when a source is applied. There are two types of flash point measurement, open cup and closed cup. In open cup devices, the sample is contained in a cup which is heated and, at intervals. The measured flash point will vary with the height of the flame above the liquid surface and, at sufficient height. The best-known example is the Cleveland open cup, in both these types, the cups are sealed with a lid through which the ignition source can be introduced. Closed cup testers normally give lower values for the point than open cup and are a better approximation to the temperature at which the vapour pressure reaches the lower flammable limit. The flash point is an empirical measurement rather than a physical parameter. The measured value will vary with equipment and test protocol variations, including temperature ramp rate, time allowed for the sample to equilibrate, sample volume, methods for determining the flash point of a liquid are specified in many standards. For example, testing by the Pensky-Martens closed cup method is detailed in ASTM D93, IP34, ISO2719, DIN51758, JIS K2265 and AFNOR M07-019. Determination of flash point by the Small Scale closed cup method is detailed in ASTM D3828 and D3278, EN ISO3679 and 3680, cEN/TR15138 Guide to Flash Point Testing and ISO TR29662 Guidance for Flash Point Testing cover the key aspects of flash point testing. Gasoline is a used in a spark-ignition engine
Flash point
–
Flaming cocktails with a flash point lower than room temperature.
Flash point
–
Automatic flash point tester according to
Pensky-Martens closed cup method with an integrated fire extinguisher.
22.
Threshold limit value
–
The threshold limit value of a chemical substance is a level to which it is believed a worker can be exposed day after day for a working lifetime without adverse effects. Strictly speaking, TLV is a term of the American Conference of Governmental Industrial Hygienists. TLVs issued by the ACGIH are the most widely accepted occupational exposure limits both in the United States and most other countries. However, it is loosely used to refer to other similar concepts used in occupational health and toxicology, such as acceptable daily intake. TLVs, along with biological exposure indices, are published annually by the ACGIH, the TLV is an estimate based on the known toxicity in humans or animals of a given chemical substance, and the reliability and accuracy of the latest sampling and analytical methods. It is not a definition since new research can often modify the risk assessment of substances. The TLV is a recommendation by ACGIH, with only a guideline status, as such, it should not be confused with exposure limits having a regulatory status, like those published and enforced by the Occupational Safety and Health Administration. The National Institute for Occupational Safety and Health publishes recommended exposure limits which OSHA takes into consideration when promulgating new regulatory exposure limits, the TLV for chemical substances is defined as a concentration in air, typically for inhalation or skin exposure. Its units are in parts per million for gases and in milligrams per cubic meter for such as dust, smoke. The basic formula for converting between ppm and mg/m³ for gases is ppm = *24.45 / molecular weight and this formula is not applicable to airborne particles. TLVs for physical agents include those for noise exposure, vibration, ionizing and non-ionizing radiation exposure and heat, the TLVs and most other occupational exposure limits are based on available toxicology and epidemiology data to protect nearly all workers over a working lifetime. The exposure assessment is initiated by selecting the appropriate exposure limit averaging time, typically the statistic for deciding acceptable exposure is chosen to be the majority of all exposures to be below the selected occupational exposure limit
Threshold limit value
–
Simple representation of exposure risk assessment and management hierarchy based on available information
23.
IDLH
–
Examples include smoke or other poisonous gases at sufficiently high concentrations. It is calculated using the LD50 or LC50, IDLH values are often used to guide the selection of breathing apparatus that are made available to workers or firefighters in specific situations. The NIOSH definition does not include oxygen deficiency although atmosphere-supplying breathing apparatus is also required, examples include high altitudes and unventilated, confined spaces. It also uses the broader term impair, rather than prevent, for example, blinding but non-toxic smoke could be considered IDLH under the OSHA definition if it would impair the ability to escape a dangerous but not life-threatening atmosphere. The OSHA definition is part of a standard, which is the minimum legal requirement. If the concentration of substances is IDLH, the worker must use the most reliable respirators. Such respirators should not use cartridges or canister with the sorbent, in addition, the respirator must maintain positive pressure under the mask during inspiration, as this will prevent the leakage of unfiltered air through the gaps. The following examples are listed in reference to IDLH values, NIOSH IDLH site 1910.134 Respiratory protection definitions
IDLH
–
Pressure-demand supplied-air respirator equipped with a full facepiece in combination with an auxiliary pressure-demand self-contained breathing apparatus - for IDLH conditions in workplace.
IDLH
–
Pressure-demand self-contained breathing apparatus with a full facepiece - for IDLH conditions in workplace.
24.
Aromatic hydrocarbon
–
An aromatic hydrocarbon or arene is a hydrocarbon with sigma bonds and delocalized pi electrons between carbon atoms forming a circle. In contrast, aliphatic hydrocarbons lack this delocalization, the term aromatic was assigned before the physical mechanism determining aromaticity was discovered, the term was coined as such simply because many of the compounds have a sweet or pleasant odour. The configuration of six carbon atoms in compounds is known as a benzene ring, after the simplest possible such hydrocarbon. Aromatic hydrocarbons can be monocyclic or polycyclic, some non-benzene-based compounds called heteroarenes, which follow Hückels rule, are also called aromatic compounds. In these compounds, at least one atom is replaced by one of the heteroatoms oxygen, nitrogen. Benzene, C6H6, is the simplest aromatic hydrocarbon, and it was the first one named as such, the nature of its bonding was first recognized by August Kekulé in the 19th century. Each carbon atom in the cycle has four electrons to share. One goes to the atom, and one each to the two neighbouring carbons. The structure is alternatively illustrated as a circle around the inside of the ring to show six electrons floating around in delocalized molecular orbitals the size of the ring itself. This depiction represents the equivalent nature of the six carbon–carbon bonds all of bond order 1.5, the electrons are visualized as floating above and below the ring with the electromagnetic fields they generate acting to keep the ring flat. The proper use of the symbol is debated, it is used to describe any cyclic π system in some publications, jensen argues that, in line with Robinsons original proposal, the use of the circle symbol should be limited to monocyclic 6 π-electron systems. In this way the symbol for a six-center six-electron bond can be compared to the Y symbol for a three-center two-electron bond. A reaction that forms a compound from an unsaturated or partially unsaturated cyclic precursor is simply called an aromatization. Many laboratory methods exist for the synthesis of arenes from non-arene precursors. Many methods rely on cycloaddition reactions, alkyne trimerization describes the cyclization of three alkynes, in the Dötz reaction an alkyne, carbon monoxide and a chromium carbene complex are the reactants. Diels–Alder reactions of alkynes with pyrone or cyclopentadienone with expulsion of carbon dioxide or carbon monoxide also form arene compounds, in Bergman cyclization the reactants are an enyne plus a hydrogen donor. Arenes are reactants in many organic reactions, in aromatic substitution one substituent on the arene ring, usually hydrogen, is replaced by another substituent. The two main types are electrophilic aromatic substitution when the reagent is an electrophile and nucleophilic aromatic substitution when the reagent is a nucleophile
Aromatic hydrocarbon
25.
Xylene
–
Xylene, xylol or dimethylbenzene is any one of three isomers of dimethylbenzene, or a combination thereof. With the formula 2C6H4, each of the three compounds has a benzene ring with two methyl groups attached at substituents. They are all colorless, flammable liquids, some of which are of great industrial value, the mixture is referred to as both xylene and, more precisely, xylenes. Xylenes are an important petrochemical produced by reforming and also by coal carbonisation in the manufacture of coke fuel. They also occur in oil in concentrations of about 0. 5–1%. Small quantities occur in gasoline and aircraft fuels, xylenes are produced mainly as part of the BTX aromatics extracted from the product of catalytic reforming known as reformate. The xylene mixture is a greasy, colorless liquid commonly encountered as a solvent. Several million tons are produced annually, in 2011, a global consortium began construction of one of the world’s largest xylene plants in Singapore. Xylene was first isolated and named in 1850 by the French chemist Auguste Cahours, Xylene exists in three isomeric forms. The isomers can be distinguished by the designations ortho-, meta-, and para-, of the three isomers, the p-isomer is the most industrially sought after since it can be oxidized to terephthalic acid. Xylenes are produced by the methylation of toluene and benzene, commercial or laboratory grade xylene produced usually contains about 40-65% of m-xylene and up to 20% each of o-xylene, p-xylene and ethylbenzene. The ratio of isomers can be shifted to favor the highly valued p-xylene via the patented UOP-Isomar process or by transalkylation of xylene with itself or trimethylbenzene and these conversions are catalyzed by zeolites. The chemical and physical properties of xylene differ according to the respective isomers, the melting point ranges from −47.87 °C to 13.26 °C. The boiling point for each isomer is around 140 °C, the density of each isomer is around 0.87 g/mL and thus is less dense than water. Xylene in air can be smelled at concentrations as low as 0.08 to 3.7 ppm, xylenes form azeotropes with water and a variety of alcohols. With water the azeotrope consists of 60% xylenes and boils at 94.5 °C, as with many alkylbenzene compounds, xylenes form complexes with various halocarbons. The complexes of different isomers often have different properties from each other. P-Xylene is the precursor to terephthalic acid and dimethyl terephthalate
Xylene
–
The xylene isomers
26.
Naphthalene
–
Naphthalene is an organic compound with formula C 10H8. It is the simplest polycyclic aromatic hydrocarbon, and is a crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromatic hydrocarbon, naphthalenes structure consists of a pair of benzene rings. It is best known as the ingredient of traditional mothballs. In the early 1820s, two separate reports described a white solid with a pungent odor derived from the distillation of coal tar, in 1821, John Kidd cited these two disclosures and then described many of this substances properties and the means of its production. He proposed the name naphthaline, as it had been derived from a kind of naphtha, naphthalenes chemical formula was determined by Michael Faraday in 1826. The structure of two fused benzene rings was proposed by Emil Erlenmeyer in 1866, and confirmed by Carl Gräbe three years later, a naphthalene molecule can be viewed as the fusion of a pair of benzene rings. As such, naphthalene is classified as a polycyclic aromatic hydrocarbon. There are two sets of equivalent hydrogen atoms, the positions are numbered 1,4,5, and 8, and the beta positions,2,3,6. Unlike benzene, the bonds in naphthalene are not of the same length. The bonds C1−C2, C3−C4, C5−C6 and C7−C8 are about 1.37 Å in length and this difference, established by X-ray diffraction, is consistent with the valence bond model in naphthalene and in particular, with the theorem of cross-conjugation. This theorem would describe naphthalene as an aromatic benzene unit bonded to a diene, as such, naphthalene possesses several resonance structures. Two isomers are possible for mono-substituted naphthalenes, corresponding to substitution at an alpha or beta position, bicyclodecapentaene is a structural isomer with a fused 4–8 ring system. In electrophilic aromatic substitution reactions, naphthalene reacts more readily than benzene, for example, chlorination and bromination of naphthalene proceeds without a catalyst to give 1-chloronaphthalene and 1-bromonaphthalene, respectively. In terms of regiochemistry, electrophiles attack occurs at the alpha position, for beta substitution, the intermediate has only six resonance structures, and only two of these are aromatic. Sulfonation, however, gives a mixture of the alpha product 1-naphthalenesulfonic acid, the 1-isomer forms predominantly at 25 °C, and the 2-isomer at 160 °C. Sulfonation to give the 1- and 2-sulfonic acid occurs readily, H 2SO4 + C 10H8 → C 10H 7−SO 3H + H 2O Further sulfonation occurs to give di-, tri- and these 1, 8-dilithio derivatives are precursors to a host of peri-naphthalene derivatives. With alkali metals, naphthalene forms the dark blue-green radical anion salts such as sodium naphthalenide, the naphthalenide salts are strong reducing agents
Naphthalene
27.
Methylcyclohexane
–
Methylcyclohexane is an organic compound with the molecular formula is CH3C6H11. Classified as saturated hydrocarbon, it is a liquid with a faint odor. Methylcyclohexane is used as a solvent and it is mainly converted in naphtha reformers to toluene. It is also one of a host substances in jet fuel surrogate blends, methylcyclohexane has no particular applications, although it used as an organic solvent, with properties similar to related saturated hydrocarbons such as heptane. Methylcyclohexane is a monosubstituted cyclohexane because it has one branching via the attachment of one group on one carbon of the cyclohexane ring. Like all cyclohexanes, it can interconvert rapidly between two chair conformers, the lowest energy form of this monosubstituted methylcyclohexane occurs when the methyl group occupies an equatorial rather than an axial position. This equilibrium is embodied in the concept of A value, in the axial position, the methyl group experiences steric crowding because of the presence of axial hydrogen atoms on the same side of the ring. There are two such interactions, with each pairwise methyl/hydrogen combination contributing approximately 7.61 kJ/mol of strain energy, the equatorial conformation experiences no such interaction, and so it is the energetically favored conformation. Like all hydrocarbons, methylcyclohexane is flammable, furthermore, it is considered very toxic to aquatic life. Note, while methylcyclohexane is a substructure of 4-methylcyclohexanemethanol, it is distinct in its physical, chemical, and biological properties
Methylcyclohexane
28.
Dielectric constant
–
The relative permittivity of a material is its permittivity expressed as a ratio relative to the permittivity of vacuum. Permittivity is a property that affects the Coulomb force between two point charges in the material. Relative permittivity is the factor by which the field between the charges is decreased relative to vacuum. Likewise, relative permittivity is the ratio of the capacitance of a capacitor using that material as a dielectric, relative permittivity is also commonly known as dielectric constant, a term deprecated in physics and engineering as well as in chemistry. Relative permittivity is typically denoted as εr and is defined as ε r = ε ε0, where ε is the complex frequency-dependent absolute permittivity of the material, and ε0 is the vacuum permittivity. Relative permittivity is a number that is in general complex-valued, its real and imaginary parts are denoted as. The relative permittivity of a medium is related to its electric susceptibility, χe, in anisotropic media the relative permittivity is a second rank tensor. The relative permittivity of a material for a frequency of zero is known as its relative permittivity. The historical term for the relative permittivity is dielectric constant and it is still commonly used, but has been deprecated by standards organizations, because of its ambiguity, as some older authors used it for the absolute permittivity ε. The permittivity may be quoted either as a property or as a frequency-dependent variant. It has also used to refer to only the real component εr of the complex-valued relative permittivity. In the causal theory of waves, permittivity is a complex quantity, the imaginary part corresponds to a phase shift of the polarization P relative to E and leads to the attenuation of electromagnetic waves passing through the medium. By definition, the relative permittivity of vacuum is equal to 1. The relative static permittivity, εr, can be measured for static electric fields as follows, first the capacitance of a test capacitor, then, using the same capacitor and distance between its plates, the capacitance Cx with a dielectric between the plates is measured. The relative dielectric constant can be calculated as ε r = C x C0. For time-variant electromagnetic fields, this quantity becomes frequency-dependent, an indirect technique to calculate εr is conversion of radio frequency S-parameter measurement results. A description of frequently used S-parameter conversions for determination of the frequency-dependent εr of dielectrics can be found in this bibliographic source, alternatively, resonance based effects may be employed at fixed frequencies. The relative permittivity is a piece of information when designing capacitors
Dielectric constant
–
Temperature dependence of the relative static permittivity of water
29.
UV/VIS spectroscopy
–
Ultraviolet–visible spectroscopy or ultraviolet-visible spectrophotometry refers to absorption spectroscopy or reflectance spectroscopy in the ultraviolet-visible spectral region. This means it uses light in the visible and adjacent ranges, the absorption or reflectance in the visible range directly affects the perceived color of the chemicals involved. In this region of the spectrum, atoms and molecules undergo electronic transitions. Molecules containing π-electrons or non-bonding electrons can absorb the energy in the form of ultraviolet or visible light to excite electrons to higher anti-bonding molecular orbitals. Spectroscopic analysis is carried out in solutions but solids and gases may also be studied. Solutions of transition metal ions can be colored because d electrons within the atoms can be excited from one electronic state to another. The colour of metal ion solutions is strongly affected by the presence of other species, for instance, the colour of a dilute solution of copper sulfate is a very light blue, adding ammonia intensifies the colour and changes the wavelength of maximum absorption. Organic compounds, especially those with a degree of conjugation. The solvents for these determinations are often water for water-soluble compounds, solvent polarity and pH can affect the absorption spectrum of an organic compound. Tyrosine, for example, increases in absorption maxima and molar extinction coefficient when pH increases from 6 to 13 or when solvent polarity decreases, while charge transfer complexes also give rise to colours, the colours are often too intense to be used for quantitative measurement. The Beer-Lambert law states that the absorbance of a solution is directly proportional to the concentration of the species in the solution. Thus, for a path length, UV/Vis spectroscopy can be used to determine the concentration of the absorber in a solution. It is necessary to know how quickly the absorbance changes with concentration and this can be taken from references, or more accurately, determined from a calibration curve. A UV/Vis spectrophotometer may be used as a detector for HPLC, the presence of an analyte gives a response assumed to be proportional to the concentration. For accurate results, the response to the analyte in the unknown should be compared with the response to a standard. The response for a concentration is known as the response factor. The wavelengths of absorption peaks can be correlated with the types of bonds in a molecule and are valuable in determining the functional groups within a molecule. The spectrum alone is not, however, a specific test for any given sample, the nature of the solvent, the pH of the solution, temperature, high electrolyte concentrations, and the presence of interfering substances can influence the absorption spectrum
UV/VIS spectroscopy
–
Beckman DU640 UV/Vis spectrophotometer.
UV/VIS spectroscopy
–
An example of a UV/Vis readout
30.
Infrared spectroscopy
–
Infrared spectroscopy involves the interaction of infrared radiation with matter. It covers a range of techniques, mostly based on absorption spectroscopy, as with all spectroscopic techniques, it can be used to identify and study chemicals. Sample may be solid, liquid, or gas, the method or technique of infrared spectroscopy is conducted with an instrument called an infrared spectrometer to produce an infrared spectrum. An IR spectrum is essentially a graph of infrared light absorbance on the vertical axis vs. frequency or wavelength on the horizontal axis, typical units of frequency used in IR spectra are reciprocal centimeters, with the symbol cm−1. Units of IR wavelength are commonly given in micrometers, symbol μm, a common laboratory instrument that uses this technique is a Fourier transform infrared spectrometer. Two-dimensional IR is also possible as discussed below, the infrared portion of the electromagnetic spectrum is usually divided into three regions, the near-, mid- and far- infrared, named for their relation to the visible spectrum. The higher-energy near-IR, approximately 14000–4000 cm−1 can excite overtone or harmonic vibrations, the mid-infrared, approximately 4000–400 cm−1 may be used to study the fundamental vibrations and associated rotational-vibrational structure. The far-infrared, approximately 400–10 cm−1, lying adjacent to the region, has low energy. The names and classifications of these subregions are conventions, and are loosely based on the relative molecular or electromagnetic properties. Infrared spectroscopy exploits the fact that molecules absorb frequencies that are characteristic of their structure and these absorptions occur at resonant frequencies, i. e. the frequency of the absorbed radiation matches the vibrational frequency. The energies are affected by the shape of the potential energy surfaces, the masses of the atoms. In particular, in the Born–Oppenheimer and harmonic approximations, i. e, the resonant frequencies are also related to the strength of the bond and the mass of the atoms at either end of it. Thus, the frequency of the vibrations are associated with a normal mode of motion. In order for a mode in a sample to be IR active. A permanent dipole is not necessary, as the rule requires only a change in dipole moment, a molecule can vibrate in many ways, and each way is called a vibrational mode. For molecules with N number of atoms, linear molecules have 3N –5 degrees of vibrational modes, as an example H2O, a non-linear molecule, will have 3 ×3 –6 =3 degrees of vibrational freedom, or modes. Simple diatomic molecules have only one bond and only one vibrational band, if the molecule is symmetrical, e. g. N2, the band is not observed in the IR spectrum, but only in the Raman spectrum. Asymmetrical diatomic molecules, e. g. CO, absorb in the IR spectrum, more complex molecules have many bonds, and their vibrational spectra are correspondingly more complex, i. e. big molecules have many peaks in their IR spectra
Infrared spectroscopy
–
Sample of an IR spec. reading; this one is from
bromomethane (CH 3 Br), showing peaks around 3000, 1300, and 1000 cm −1 (on the horizontal axis).
31.
NMR spectroscopy
–
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is a research technique that exploits the magnetic properties of certain atomic nuclei. This type of spectroscopy determines the physical and chemical properties of atoms or the molecules in which they are contained and it relies on the phenomenon of nuclear magnetic resonance and can provide detailed information about the structure, dynamics, reaction state, and chemical environment of molecules. Suitable samples range from small compounds analyzed with 1-dimensional proton or carbon-13 NMR spectroscopy to large proteins or nucleic acids using 3 or 4-dimensional techniques. The impact of NMR spectroscopy on the sciences has been substantial because of the range of information, NMR spectra are unique, well-resolved, analytically tractable and often highly predictable for small molecules. Thus, in organic chemistry practice, NMR analysis is used to confirm the identity of a substance, different functional groups are obviously distinguishable, and identical functional groups with differing neighboring substituents still give distinguishable signals. NMR has largely replaced traditional wet chemistry tests such as reagents or typical chromatography for identification. A disadvantage is that a large amount, 2–50 mg, of a purified substance is required. Preferably, the sample should be dissolved in a solvent, because NMR analysis of solids requires a dedicated MAS machine, the timescale of NMR is relatively long, and thus it is not suitable for observing fast phenomena, producing only an averaged spectrum. NMR spectrometers are relatively expensive, universities usually have them, modern NMR spectrometers have a very strong, large and expensive liquid helium-cooled superconducting magnet, because resolution directly depends on magnetic field strength. There are even benchtop NMR spectrometers, the Purcell group at Harvard University and the Bloch group at Stanford University independently developed NMR spectroscopy in the late 1940s and early 1950s. Edward Mills Purcell and Felix Bloch shared the 1952 Nobel Prize in Physics for their discoveries, when placed in a magnetic field, NMR active nuclei absorb electromagnetic radiation at a frequency characteristic of the isotope. The resonant frequency, energy of the absorption, and the intensity of the signal are proportional to the strength of the magnetic field, for example, in a 21 Tesla magnetic field, protons resonate at 900 MHz. It is common to refer to a 21 T magnet as a 900 MHz magnet, spinning the sample is necessary to average out diffusional motion. Whereas, measurements of diffusion constants are done the sample stationary and spinning off, the vast majority of nuclei in a solution would belong to the solvent, and most regular solvents are hydrocarbons and would contain NMR-reactive protons. The most used deuterated solvent is deuterochloroform, although deuterium oxide and deuterated DMSO are used for hydrophilic analytes, the chemical shifts are slightly different in different solvents, depending on electronic solvation effects. NMR spectra are often calibrated against the known solvent residual proton peak instead of added tetramethylsilane, to detect the very small frequency shifts due to nuclear magnetic resonance, the applied magnetic field must be constant throughout the sample volume. High resolution NMR spectrometers use shims to adjust the homogeneity of the field to parts per billion in a volume of a few cubic centimeters. In order to detect and compensate for inhomogeneity and drift in the magnetic field, in modern NMR spectrometers shimming is adjusted automatically, though in some cases the operator has to optimize the shim parameters manually to obtain the best possible resolution
NMR spectroscopy
–
A 900MHz NMR instrument with a 21.1
T magnet at
HWB-NMR, Birmingham, UK
NMR spectroscopy
–
The NMR sample is prepared in a thin-walled glass tube - an
NMR tube.
NMR spectroscopy
–
1 H NMR spectrum of
menthol with
chemical shift in ppm on the horizontal axis. Each magnetically inequivalent proton has a characteristic shift, and couplings to other protons appear as splitting of the peaks into multiplets: e.g. peak a, because of the three magnetically equivalent protons in methyl group a, couple to one adjacent proton (e) and thus appears as a doublet.
32.
Mass spectrometry
–
Mass spectrometry is an analytical technique that ionizes chemical species and sorts the ions based on their mass-to-charge ratio. In simpler terms, a mass spectrum measures the masses within a sample, mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures. A mass spectrum is a plot of the ion signal as a function of the mass-to-charge ratio, in a typical MS procedure, a sample, which may be solid, liquid, or gas, is ionized, for example by bombarding it with electrons. This may cause some of the molecules to break into charged fragments. The ions are detected by a capable of detecting charged particles. Results are displayed as spectra of the abundance of detected ions as a function of the mass-to-charge ratio. The atoms or molecules in the sample can be identified by correlating known masses to the masses or through a characteristic fragmentation pattern. Goldstein called these positively charged anode rays Kanalstrahlen, the translation of this term into English is canal rays. Wien found that the charge-to-mass ratio depended on the nature of the gas in the discharge tube, thomson later improved on the work of Wien by reducing the pressure to create the mass spectrograph. The word spectrograph had become part of the international scientific vocabulary by 1884, a mass spectroscope is similar to a mass spectrograph except that the beam of ions is directed onto a phosphor screen. A mass spectroscope configuration was used in early instruments when it was desired that the effects of adjustments be quickly observed, once the instrument was properly adjusted, a photographic plate was inserted and exposed. The term mass spectroscope continued to be used though the direct illumination of a phosphor screen was replaced by indirect measurements with an oscilloscope. The use of the mass spectroscopy is now discouraged due to the possibility of confusion with light spectroscopy. Mass spectrometry is often abbreviated as mass-spec or simply as MS, modern techniques of mass spectrometry were devised by Arthur Jeffrey Dempster and F. W. Aston in 1918 and 1919 respectively. Sector mass spectrometers known as calutrons were used for separating the isotopes of uranium developed by Ernest O. Lawrence during the Manhattan Project, calutron mass spectrometers were used for uranium enrichment at the Oak Ridge, Tennessee Y-12 plant established during World War II. In 1989, half of the Nobel Prize in Physics was awarded to Hans Dehmelt, a mass spectrometer consists of three components, an ion source, a mass analyzer, and a detector. The ionizer converts a portion of the sample into ions, there is a wide variety of ionization techniques, depending on the phase of the sample and the efficiency of various ionization mechanisms for the unknown species. An extraction system removes ions from the sample, which are then targeted through the mass analyzer, the differences in masses of the fragments allows the mass analyzer to sort the ions by their mass-to-charge ratio
Mass spectrometry
–
SIMS mass spectrometer, model IMS 3f.
Mass spectrometry
–
Orbitrap mass spectrometer.
Mass spectrometry
–
Replica of J.J. Thompson's third mass spectrometer.
Mass spectrometry
–
Calutron mass spectrometers were used in the Manhattan Project for uranium enrichment.
33.
Water (molecule)
–
Water is a polar inorganic compound that is at room temperature a tasteless and odorless liquid, nearly colorless with a hint of blue. This simplest hydrogen chalcogenide is by far the most studied chemical compound and is described as the solvent for its ability to dissolve many substances. This allows it to be the solvent of life and it is the only common substance to exist as a solid, liquid, and gas in nature. Water molecules form hydrogen bonds with other and are strongly polar. This polarity allows it to separate ions in salts and strongly bond to other substances such as alcohols and acids. Water is amphoteric, meaning it is both an acid and a base—it produces H+ and OH− ions by self ionization and this regulates the concentrations of H+ and OH− ions in water. Due to water being a good solvent, it is rarely pure. However, there are many compounds that are essentially, if not completely, insoluble in water, such as fats, oils. The accepted IUPAC name of water is oxidane or simply water, or its equivalent in different languages, oxidane is only intended to be used as the name of the mononuclear parent hydride used for naming derivatives of water by substituent nomenclature. These derivatives commonly have other recommended names, for example, the name hydroxyl is recommended over oxidanyl for the –OH group. The name oxane is explicitly mentioned by the IUPAC as being unsuitable for this purpose, the simplest systematic name of water is hydrogen oxide. This is analogous to related compounds such as hydrogen peroxide, hydrogen sulfide, the polarized form of the water molecule, H+OH−, is also called hydron hydroxide by IUPAC nomenclature. It is a rarely used name of water, and mostly used in various hoaxes or spoofs that call for this chemical to be banned. Other systematic names for water include hydroxic acid, hydroxylic acid, none of these exotic names are used widely. Water is the substance with chemical formula H 2O, one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom. Water is a tasteless, odorless liquid at ambient temperature and pressure, ice also appears colorless, and water vapor is essentially invisible as a gas. The elements surrounding oxygen in the table, nitrogen, fluorine, phosphorus, sulfur and chlorine. The reason that water forms a liquid is that oxygen is more electronegative than all of elements with the exception of fluorine
Water (molecule)
Water (molecule)
–
Water (H 2 O)
Water (molecule)
–
Dew drops adhering to a
spider web
Water (molecule)
–
This
paper clip is under the water level, which has risen gently and smoothly. Surface tension prevents the clip from submerging and the water from overflowing the glass edges.
34.
Methyl group
–
A methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms — CH3. In formulas, the group is often abbreviated Me, such hydrocarbon groups occur in many organic compounds. It is a stable group in most molecules. While the methyl group is part of a larger molecule. The anion has eight electrons, the radical seven and the cation six. All three forms are highly reactive and rarely observed, the methylium cation exists in the gas phase, but is otherwise not encountered. Some compounds are considered to be sources of the CH3+ cation, the methanide anion exists only in rarefied gas phase or under exotic conditions. It can be produced by electrical discharge in ketene at low pressure, such reagents are generally prepared from the methyl halides, M + CH3X → MCH3 where M is an alkali metal. The methyl radical has the formula CH3 and it exists in dilute gases, but in more concentrated form it readily dimerizes to ethane. It can be produced by decomposition of only certain compounds. The reactivity of a methyl group depends on the adjacent substituents, methyl groups can be quite unreactive. For example, in compounds, the methyl group resists attack by even the strongest acids. The oxidation of a group occurs widely in nature and industry. The oxidation products derived from methyl are CH2OH, CHO, for example, permanganate often converts a methyl group to a carboxyl group, e. g. the conversion of toluene to benzoic acid. Ultimately oxidation of methyl groups gives protons and carbon dioxide, as seen in combustion, demethylation is a common process, and reagents that undergo this reaction are called methylating agents. Common methylating agents are dimethyl sulfate, methyl iodide, and methyl triflate, methanogenesis, the source of natural gas, arises via a demethylation reaction. Certain methyl groups can be deprotonated, for example, the acidity of the methyl groups in acetone is about 1020 more acidic than methane. The resulting carbanions are key intermediates in many reactions in organic synthesis and biosynthesis, fatty acids are produced in this way
Methyl group
–
Different ways of representing a methyl group (highlighted in blue)
35.
Feedstock
–
As feedstock, the term connotes these materials are bottleneck assets and are highly important with regards to producing other products. This phenomenon, known as Dutch disease or the resource curse, an example of this is the geological scandal of the Democratic Republic of Congo as it is rich in raw materials, the Second Congo War focused on controlling these raw materials. Raw materials are used by non-humans, such as birds using found objects. Karl Marx, Capital, Vol.1, Part III, Chap
Feedstock
–
Anthracite coal stockpile at the shipping area of a mid-slope
coal processing plant. The road leading up beyond the stockpile leads down from a
Mountain top strip mine which sources the materials.
Feedstock
–
Latex being collected from a
tapped rubber tree
36.
Contact cement
–
The use of adhesives offers many advantages over binding techniques such as sewing, mechanical fastening, thermal bonding, etc. Adhesives are typically organized by the method of adhesion and these are then organized into reactive and non-reactive adhesives, which refers to whether the adhesive chemically reacts in order to harden. Alternatively they can be organized by whether the raw stock is of natural or synthetic origin, Adhesives may be found naturally or produced synthetically. The earliest human use of substances was approximately 200,000 years ago. The first references to adhesives in literature first appeared in approximately 2000 BCE, the Greeks and Romans made great contributions to the development of adhesives. In Europe, glue was not widely used until the period 1500–1700 CE, from then until the 1900s increases in adhesive use and discovery were relatively gradual. Only since the last century has the development of synthetic adhesives accelerated rapidly, the earliest use of adhesives was discovered in central Italy when two stone flakes partially covered with birch-bark tar and a third uncovered stone from the Middle Pleistocene era were found. This is thought to be the oldest discovered human use of tar-hafted stones, the birch-bark-tar adhesive is a simple, one-component adhesive. Although sticky enough, plant-based adhesives are brittle and vulnerable to environmental conditions, the first use of compound adhesives was discovered in Sibudu, South Africa. The ability to produce stronger adhesives allowed middle stone age humans to attach stone segments to sticks in greater variations, more recent examples of adhesive use by prehistoric humans have been found at the burial sites of ancient tribes. Archaeologists studying the sites found that approximately 6,000 years ago the tribesmen had buried their dead together with food found in clay pots repaired with tree resins. The glue was analyzed as pitch, which requires the heating of tar during its production, the retrieval of this tar requires a transformation of birch bark by means of heat, in a process known as pyrolysis. The first references to adhesives in literature first appeared in approximately 2000 BCE, further historical records of adhesive use are found from the period spanning 1500–1000 BCE. Artifacts from this period include paintings depicting wood gluing operations and a made of wood. Other ancient Egyptian artifacts employ animal glue for bonding or lamination, such lamination of wood for bows and furniture is thought to have extended their life and was accomplished using casein -based glues. The ancient Egyptians also developed starch-based pastes for the bonding of papyrus to clothing, from 1 to 500 AD the Greeks and Romans made great contributions to the development of adhesives. Wood veneering and marquetry were developed, the production of animal and fish glues refined, egg-based pastes were used to bond gold leaves incorporated various natural ingredients such as blood, bone, hide, milk, cheese, vegetables, and grains. The Greeks began the use of slaked lime as mortar while the Romans furthered mortar development by mixing lime with volcanic ash and this material, known as pozzolanic cement, was used in the construction of the Roman Colosseum and Pantheon
Contact cement
–
Nitrocellulose adhesive outside a tube
Contact cement
–
A reconstruction of Ötzi's axe
Contact cement
–
Beeswax
Contact cement
–
Modern Slaked
Lime Factory in Ukraine
37.
Pine
–
A pine is any conifer in the genus Pinus, /ˈpiːnuːs/, of the family Pinaceae. Pinus is the genus in the subfamily Pinoideae. The Plant List compiled by the Royal Botanic Gardens, Kew and Missouri Botanical Garden accepts 126 species names of pines as current, together with 35 unresolved species, the modern English name pine derives from Latin pinus, which some have traced to the Indo-European base *pīt- ‘resin’. Before the 19th century, pines were often referred to as firs, the genus is divided into three subgenera, which can be distinguished by cone, seed, and leaf characters, Pinus subg. Pinus, the yellow, or hard pine group, generally harder wood. Ducampopinus, the foxtail or pinyon group Pinus subg, strobus, the white, or soft pine group, generally with softer wood and five needles per fascicle Most regions of the Northern Hemisphere host some native species of pines. One species crosses the equator in Sumatra to 2°S, in North America, various species occur in regions at latitudes from as far north as 66°N to as far south as 12°N. Various species have been introduced to temperate and subtropical regions of both hemispheres, where they are grown as timber or cultivated as ornamental plants in parks, a number of such introduced species have become invasive and threaten native ecosystems. Pine trees are evergreen, coniferous trees growing 3–80 m tall. The smallest are Siberian dwarf pine and Potosi pinyon, and the tallest is a 81.79 m tall ponderosa pine located in southern Oregons Rogue River-Siskiyou National Forest, the bark of most pines is thick and scaly, but some species have thin, flaky bark. The branches are produced in regular pseudo whorls, actually a very tight spiral, the spiral growth of branches, needles, and cone scales are arranged in Fibonacci number ratios. The new spring shoots are sometimes called candles, they are covered in brown or whitish bud scales and point upward at first, then turn green. These candles offer foresters a means to evaluate fertility of the soil, pines are long-lived, and typically reach ages of 100–1,000 years, some even more. The longest-lived is the Great Basin bristlecone pine, Pinus longaeva, one individual of this species, dubbed Methuselah, is one of the worlds oldest living organisms at around 4,600 years old. This tree can be found in the White Mountains of California, an older tree, now cut down, was dated at 4,900 years old. It was discovered in a grove beneath Wheeler Peak and it is now known as Prometheus after the Greek immortal, pines have four types of leaf, Seed leaves on seedlings, born in a whorl of 4–24. Juvenile leaves, which follow immediately on seedlings and young plants, 2–6 cm long, single, green or often blue-green and these are produced for six months to five years, rarely longer. Scale leaves, similar to bud scales, small, brown and non-photosynthetic, needles, the adult leaves, are green and bundled in clusters called fascicles
Pine
–
Pine tree
Pine
–
A
Khasi pine in
Benguet, Philippines
Pine
–
Huangshan pine (Pinus hwangshanensis),
Anhui, China
Pine
–
Ancient
Pinus longaeva,
Nevada, USA
38.
Poles
–
The Poles are a nation and West Slavic ethnic group native to Poland who share a common ancestry, culture, history and are native speakers of the Polish language. The population of Poles in Poland is estimated at 37,394,000 out of a population of 38,538,000. Polands population inhabits several historic regions, including Greater Poland, Lesser Poland, Mazovia, Silesia, Pomerania, Kuyavia, Warmia, Masuria, a wide-ranging Polish diaspora exists throughout Europe, the Americas and in Australasia. Today the largest urban concentration of Poles is the Katowice urban agglomeration of 2.7 million inhabitants, Poland was also for centuries a refuge for many Jews from all over Europe, a large number emigrated in the twentieth century to Israel. Several prominent Israeli statesmen were born in Poland, including Israels founder David Ben-Gurion, former President of Israel Shimon Peres, the Slavic people have been in the territory of modern Poland for over 1500 years. In the 9th and 10th centuries the tribes gave rise to developed regions along the upper Vistula, the last tribal undertaking resulted in the 10th century in a lasting political structure and state, Poland, one of the West Slavic nations. After 1945 the so-called autochthonous or aboriginal school of Polish prehistory received official backing in Poland, Polish people are the sixth largest national group in the European Union. Estimates vary depending on source, though available data suggest a number of around 60 million people worldwide. There are almost 38 million Poles in Poland alone, there are also Polish minorities in the surrounding countries including Germany, and indigenous minorities in the Czech Republic, Lithuania, Ukraine, and Belarus. There are some smaller indigenous minorities in nearby countries such as Moldova, the term Polonia is usually used in Poland to refer to people of Polish origin who live outside Polish borders, officially estimated at around 10 to 20 million. There is a notable Polish diaspora in the United States, Brazil, France has a historic relationship with Poland and has a relatively large Polish-descendant population. Poles have lived in France since the 18th century, in the early 20th century, over a million Polish people settled in France, mostly during world wars, among them Polish émigrés fleeing either Nazi occupation or later Soviet rule. In the United States, a significant number of Polish immigrants settled in Chicago, Ohio, Detroit, New York City, Orlando, Pittsburgh, Buffalo, the highest concentration of Polish Americans in a single New England municipality is in New Britain, Connecticut. The majority of Polish Canadians have arrived in Canada since World War II, the number of Polish immigrants increased between 1945 and 1970, and again after the end of Communism in Poland in 1989. In Brazil the majority of Polish immigrants settled in Paraná State, smaller, but significant numbers settled in the states of Rio Grande do Sul, Espírito Santo and São Paulo. The city of Curitiba has the second largest Polish diaspora in the world and Polish music, dishes and it is estimated that over half a million Polish people have come to work in the United Kingdom from Poland. Since 2011, Poles have been able to work throughout the EU and not just in the United Kingdom, Ireland. The Polish community in Norway has increased substantially and has grown to a number of 120,000
Poles
–
Stańczyk at a Ball at Queen Bona's Court, by
Matejko, 1862
Poles
–
Nicolaus Copernicus
Poles
–
Marie Skłodowska Curie
Poles
–
Rudolf Stefan Weigl
39.
Myroxylon
–
The genus Myroxylon was originally described in 1753 by Linnaeus, such description was made using a specimen collected in the province of Cartagena, and named it Toluifera balsamum. The genus Myroxylon was first established by Linnaeus filius in 1781, latex from Myroxylon trees is the source of Balsam of Peru and Tolu balsam and composition. Some authors recognize infra-specific taxa based, mainly, in their balsam phytochemistry, there are reports of differences in composition of balsams obtained from M. balsamum, M. balsamum, and M. peruiferum. It is in the Fabaceae family of flowering plants, there are two species, M. balsamum and M. peruiferum. Myroxylon is a genus of tree grown in Central America and South America, Myroxylon balsamum occurs in Central America, and northern and western South America, it is fairly common in tropical forest at 200–690 m altitude. In Peru and Brazil this species is associated with rivers. It is found in remnants of mesophillous forest, at present it is considered as being of least concern according to CITES classification. It is found in remnants of mesophillous forest and dry habitats at 540–2000 m elevation and it is considered to be Near Threatened, according to CITES classification. The trees are large, growing to 40 metres tall, with pinnate leaves 15 centimetres long. The flowers are white with yellow stamens, produced in racemes, the fruit is a pod 7–11 centimetres long, containing a single seed. The tree is often called Quina or Balsamo, Tolu in Colombia, Quina quina in Argentina, members of this genus produce hydroxypipecolic acids in their leaves. The wood is brown, with a deep red heartwood. Natural oils grant it excellent decay resistance, in fact, it is also resistant to preservative treatment. With regard to woodworking, the tree is difficult to work but can be finished with a high natural polish. The balsam tree can become an invasive species when introduced into tropical countries where it is not native. In Sri Lanka, it has overgrown several hectares of the Udawatta Kele Sanctuary and is spreading there. The tree has also introduced to several Pacific islands such as Fiji and to Indonesia. Media related to Myroxylon at Wikimedia Commons
Myroxylon
–
Myroxylon
Myroxylon
–
Myroxylon peruiferum
40.
Electrophilic aromatic substitution
–
Electrophilic aromatic substitution is an organic reaction in which an atom that is attached to an aromatic system is replaced by an electrophile. Some of the most important electrophilic aromatic substitutions are aromatic nitration, aromatic halogenation, aromatic sulfonation, the most widely practiced example of this reaction is the ethylation of benzene. Approximately 24,700,000 tons were produced in 1999, in this process, solid acids are used as catalyst to generate the incipient carbocation. Many other electrophilic reactions of benzene are conducted, although on much smaller scale, the nitration of benzene is achieved via the action of the nitronium ion as the electrophile. The sulfonation with fuming sulfuric acid gives benzenesulfonic acid, Aromatic halogenation with bromine, chlorine, or iodine gives the corresponding aryl halides. This reaction is catalyzed by the corresponding iron or aluminum trihalide. The Friedel–Crafts reaction can be performed either as an acylation or as an alkylation, often, aluminium trichloride is used, but almost any strong Lewis acid can be applied. For the acylation reaction a stoichiometric amount of aluminum trichloride is required, both the regioselectivity and the speed of an electrophilic aromatic substitution are affected by the substituents already attached to the benzene ring. In terms of regioselectivity, some groups promote substitution at the ortho or para positions and these groups are called either ortho–para directing or meta directing. In addition, some groups will increase the rate of reaction while others will decrease the rate, while the patterns of regioselectivity can be explained with resonance structures, the influence on kinetics can be explained by both resonance structures and the inductive effect. Substituents can generally be divided into two classes regarding electrophilic substitution, activating and deactivating towards the aromatic ring, examples of activated aromatic rings are toluene, aniline and phenol. The extra electron density delivered into the ring by the substituent is not distributed evenly over the ring but is concentrated on atoms 2,4 and 6. These positions are thus the most reactive towards an electron-poor electrophile, the highest electron density is located on both ortho and para positions, although this increased reactivity might be offset by steric hindrance between substituent and electrophile. On the other hand, deactivating substituents destabilize the intermediate cation and they do so by withdrawing electron density from the aromatic ring, although the positions most affected are again the ortho and para ones. This means that the most reactive positions are the meta ones, examples of deactivated aromatic rings are nitrobenzene, benzaldehyde and trifluoromethylbenzene. The deactivation of the system also means that generally harsher conditions are required to drive the reaction to completion. An example of this is the nitration of toluene during the production of trinitrotoluene, functional groups thus usually tend to favor one or two of these positions above the others, that is, they direct the electrophile to specific positions. A functional group that tends to direct attacking electrophiles to the meta position, groups with unshared pairs of electrons, such as the amino group of aniline, are strongly activating and ortho/para-directing
Electrophilic aromatic substitution
41.
Methyl
–
A methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms — CH3. In formulas, the group is often abbreviated Me, such hydrocarbon groups occur in many organic compounds. It is a stable group in most molecules. While the methyl group is part of a larger molecule. The anion has eight electrons, the radical seven and the cation six. All three forms are highly reactive and rarely observed, the methylium cation exists in the gas phase, but is otherwise not encountered. Some compounds are considered to be sources of the CH3+ cation, the methanide anion exists only in rarefied gas phase or under exotic conditions. It can be produced by electrical discharge in ketene at low pressure, such reagents are generally prepared from the methyl halides, M + CH3X → MCH3 where M is an alkali metal. The methyl radical has the formula CH3 and it exists in dilute gases, but in more concentrated form it readily dimerizes to ethane. It can be produced by decomposition of only certain compounds. The reactivity of a methyl group depends on the adjacent substituents, methyl groups can be quite unreactive. For example, in compounds, the methyl group resists attack by even the strongest acids. The oxidation of a group occurs widely in nature and industry. The oxidation products derived from methyl are CH2OH, CHO, for example, permanganate often converts a methyl group to a carboxyl group, e. g. the conversion of toluene to benzoic acid. Ultimately oxidation of methyl groups gives protons and carbon dioxide, as seen in combustion, demethylation is a common process, and reagents that undergo this reaction are called methylating agents. Common methylating agents are dimethyl sulfate, methyl iodide, and methyl triflate, methanogenesis, the source of natural gas, arises via a demethylation reaction. Certain methyl groups can be deprotonated, for example, the acidity of the methyl groups in acetone is about 1020 more acidic than methane. The resulting carbanions are key intermediates in many reactions in organic synthesis and biosynthesis, fatty acids are produced in this way
Methyl
–
Different ways of representing a methyl group (highlighted in blue)
42.
Hydrogen
–
Hydrogen is a chemical element with chemical symbol H and atomic number 1. With a standard weight of circa 1.008, hydrogen is the lightest element on the periodic table. Its monatomic form is the most abundant chemical substance in the Universe, non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium, has one proton, the universal emergence of atomic hydrogen first occurred during the recombination epoch. At standard temperature and pressure, hydrogen is a colorless, odorless, tasteless, non-toxic, nonmetallic, since hydrogen readily forms covalent compounds with most nonmetallic elements, most of the hydrogen on Earth exists in molecular forms such as water or organic compounds. Hydrogen plays an important role in acid–base reactions because most acid-base reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a charge when it is known as a hydride. The hydrogen cation is written as though composed of a bare proton, Hydrogen gas was first artificially produced in the early 16th century by the reaction of acids on metals. Industrial production is mainly from steam reforming natural gas, and less often from more energy-intensive methods such as the electrolysis of water. Most hydrogen is used near the site of its production, the two largest uses being fossil fuel processing and ammonia production, mostly for the fertilizer market, Hydrogen is a concern in metallurgy as it can embrittle many metals, complicating the design of pipelines and storage tanks. Hydrogen gas is flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume. The enthalpy of combustion is −286 kJ/mol,2 H2 + O2 →2 H2O +572 kJ Hydrogen gas forms explosive mixtures with air in concentrations from 4–74%, the explosive reactions may be triggered by spark, heat, or sunlight. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C, the detection of a burning hydrogen leak may require a flame detector, such leaks can be very dangerous. Hydrogen flames in other conditions are blue, resembling blue natural gas flames, the destruction of the Hindenburg airship was a notorious example of hydrogen combustion and the cause is still debated. The visible orange flames in that incident were the result of a mixture of hydrogen to oxygen combined with carbon compounds from the airship skin. H2 reacts with every oxidizing element, the ground state energy level of the electron in a hydrogen atom is −13.6 eV, which is equivalent to an ultraviolet photon of roughly 91 nm wavelength. The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, however, the atomic electron and proton are held together by electromagnetic force, while planets and celestial objects are held by gravity. The most complicated treatments allow for the effects of special relativity
Hydrogen
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Purple glow in its plasma state
Hydrogen
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The
Space Shuttle Main Engine burnt hydrogen with oxygen, producing a nearly invisible flame at full thrust.
Hydrogen
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Spectral lines of hydrogen
Hydrogen
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First tracks observed in
liquid hydrogen bubble chamber at the
Bevatron
43.
P-Toluenesulfonic acid
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P-Toluenesulfonic acid or tosylic acid is an organic compound with the formula CH3C6H4SO3H. It is a solid that is soluble in water, alcohols. The CH3C6H4SO2– group is known as the group and is often abbreviated as Ts or Tos. Most often, TsOH refers to the monohydrate, TsOH. H2O, as with other sulfonic acids, TsOH is a strong organic acid. It is about one million times stronger than benzoic acid and it is one of the few strong acids that is solid and, hence, conveniently weighed. Also, unlike some strong mineral acids, TsOH is non-oxidizing, TsOH is prepared on an industrial scale by the sulfonation of toluene. Common impurities include benzenesulfonic acid and sulfuric acid, impurities can be removed by recrystallization from its concentrated aqueous solution followed by azeotropic drying with toluene. TsOH finds use in organic synthesis as an acid catalyst. Examples of uses include, Acetalization of an aldehyde, tosylate esters are used as alkylating agents because the tosyl group is electron-withdrawing, which makes the tosylate anion a good leaving group. Toluenesulfonate esters undergo nucleophilic attack or elimination, reduction of tosylate esters gives the hydrocarbon. Thus, tosylation followed by reduction allows for the deoxygenation of alcohols, TsOH may be converted to p-toluenesulfonic anhydride by heating with phosphorus pentoxide. For example, TsOH is unaffected by cold concentrated hydrochloric acid, but hydrolyzes when heated to 186 °C in concentrated phosphoric acid
P-Toluenesulfonic acid
–
p -Toluenesulfonic acid
44.
Halogenation
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Halogenation is a chemical reaction that involves the addition of one or more halogens to a compound or material. Dehalogenation is the reverse of halogenation and results in the removal of a halogen from a molecule, the pathway and stoichiometry of halogenation depends on the structural features and functional groups of the organic substrate, as well as on the specific halogen. Inorganic compounds such as metals also undergo halogenation, several pathways exist for the halogenation of organic compounds, including free radical halogenation, ketone halogenation, electrophilic halogenation, and halogen addition reaction. The structure of the substrate is one factor that determines the pathway, saturated hydrocarbons typically do not add halogens but undergo free radical halogenation, involving substitution of hydrogen atoms by halogen. The regiochemistry of the halogenation of alkanes is usually determined by the weakness of the available C–H bonds. The preference for reaction at tertiary and secondary positions results from greater stability of the free radicals. Free radical halogenation is used for the production of chlorinated methanes. Unsaturated compounds, especially alkenes and alkynes, add halogens, RCH=CHR′ + X2 → RCHX–CHXR′ The addition of halogens to alkenes proceeds via intermediate halonium ions, in special cases, such intermediates have been isolated. Aromatic compounds are subject to electrophilic halogenation, RC6H5 + X2 → HX + RC6H4X The facility of halogenation is influenced by the halogen, fluorine and chlorine are more electrophilic and are more aggressive halogenating agents. Bromine is a weaker halogenating agent than fluorine and chlorine, while iodine is least reactive of them all. The facility of hydrogenolysis follows the trend, iodine is most easily removed from organic compounds. In the Hunsdiecker reaction, from carboxylic acids are converted to the chain-shortened halide, in the Hell–Volhard–Zelinsky halogenation, carboxylic acids are alpha-halogenated. Fluorination with elemental fluorine requires highly specialised conditions and apparatus, many commercially important organic compounds are fluorinated electrochemically using hydrogen fluoride as the source of fluorine. The method is called electrochemical fluorination, aside from F2 and its electrochemically generated equivalent, a variety of fluorinating reagents are known such as xenon difluoride and cobalt fluoride. Both saturated and unsaturated compounds react directly with chlorine, the former usually requiring UV light to initiate homolysis of chlorine, chlorination is conducted on a large scale industrially, major processes include routes to 1, 2-dichloroethane, as well as various chlorinated ethanes, as solvents. Bromination is more selective than chlorination because the reaction is less exothermic, most commonly bromination is conducted by the addition of Br2 to alkenes. An example of bromination is the synthesis of the anesthetic halothane from trichloroethylene, Organobromine compounds are the most common organohalides in nature. Their formation is catalyzed by the enzyme bromoperoxidase which utilizes bromide in combination with oxygen as an oxidant, the oceans are estimated to release 1–2 million tons of bromoform and 56,000 tons of bromomethane annually
Halogenation
–
Structure of a
bromonium ion
45.
Chlorine
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Chlorine is a chemical element with symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the table and its properties are mostly intermediate between them. Chlorine is a gas at room temperature. It is an extremely reactive element and a strong oxidising agent, among the elements, it has the highest electron affinity, the most common compound of chlorine, sodium chloride, has been known since ancient times. Around 1630, chlorine gas was first synthesised in a chemical reaction, Carl Wilhelm Scheele wrote a description of chlorine gas in 1774, supposing it to be an oxide of a new element. In 1809, chemists suggested that the gas might be an element, and this was confirmed by Sir Humphry Davy in 1810. Because of its reactivity, all chlorine in the Earths crust is in the form of ionic chloride compounds. It is the second-most abundant halogen and twenty-first most abundant chemical element in Earths crust and these crustal deposits are nevertheless dwarfed by the huge reserves of chloride in seawater. Elemental chlorine is produced from brine by electrolysis. The high oxidising potential of chlorine led to the development of commercial bleaches and disinfectants. As a common disinfectant, elemental chlorine and chlorine-generating compounds are used directly in swimming pools to keep them clean. Elemental chlorine at high concentrations is extremely dangerous and poisonous for all living organisms, in the form of chloride ions, chlorine is necessary to all known species of life. Other types of compounds are rare in living organisms. In the upper atmosphere, chlorine-containing organic molecules such as chlorofluorocarbons have been implicated in ozone depletion, small quantities of elemental chlorine are generated by oxidation of chloride to hypochlorite in neutrophils as part of the immune response against bacteria. Its importance in food was very well known in antiquity and was sometimes used as payment for services for Roman generals. Around 1630, chlorine was recognized as a gas by the Flemish chemist, the element was first studied in detail in 1774 by Swedish chemist Carl Wilhelm Scheele, and he is credited with the discovery. He called it dephlogisticated muriatic acid air since it is a gas and he failed to establish chlorine as an element, mistakenly thinking that it was the oxide obtained from the hydrochloric acid. He named the new element within this oxide as muriaticum, in 1809, Joseph Louis Gay-Lussac and Louis-Jacques Thénard tried to decompose dephlogisticated muriatic acid air by reacting it with charcoal to release the free element muriaticum
Chlorine
–
A glass container filled with chlorine gas
Chlorine
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Chlorine, liquefied under a pressure of 7.4 bar at room temperature, displayed in a quartz ampule embedded in
acrylic glass.
Chlorine
–
Carl Wilhelm Scheele
Chlorine
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Liquid chlorine analysis
46.
Iron(III) chloride
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Iron chloride, also called ferric chloride, is an industrial scale commodity chemical compound, with the formula FeCl3 and with iron in the +3 oxidation state. The colour of iron chloride crystals depends on the angle, by reflected light the crystals appear dark green. Anhydrous iron chloride is deliquescent, forming hydrated hydrogen chloride mists in moist air and it is rarely observed in its natural form, the mineral molysite, known mainly from some fumaroles. When dissolved in water, iron chloride undergoes hydrolysis and gives off heat in an exothermic reaction, the resulting brown, acidic, and corrosive solution is used as a flocculant in sewage treatment and drinking water production, and as an etchant for copper-based metals in printed circuit boards. Anhydrous iron chloride is a fairly strong Lewis acid, and it is used as a catalyst in organic synthesis, the descriptor hydrated or anhydrous is used when referring to iron chloride, to distinguish between the two common forms. The hexahydrate is usually given as the empirical formula FeCl3⋅6H2O. It may also be given as trans-Cl⋅2H2O and the systematic name tetraaquadichloroiron chloride dihydrate, anhydrous iron chloride adopts the BiI3 structure, which features octahedral Fe centres interconnected by two-coordinate chloride ligands. Iron chloride hexahydrate consists of trans-+ cationic complexes and chloride anions, Iron chloride has a relatively low melting point and boils at around 315 °C. Anhydrous iron chloride may be prepared by union of the elements,2 Fe +3 Cl2 →2 FeCl3 Solutions of iron chloride are produced both from iron and from ore, in a closed-loop process. Conversion of the hydrate to anhydrous iron chloride is not accomplished by heating, as HCl, Iron chloride undergoes hydrolysis to give an acidic solution. When heated with iron oxide at 350 °C, iron chloride gives iron oxychloride, FeCl3 + Fe2O3 →3 FeOCl It is a moderately strong Lewis acid, forming adducts with Lewis bases such as triphenylphosphine oxide, e. g. FeCl32 where Ph = phenyl. It also reacts with other salts to give the yellow tetrahedral FeCl4− ion. Salts of FeCl4− in hydrochloric acid can be extracted into diethyl ether, alkali metal alkoxides react to give the metal alkoxide complexes of varying complexity. The compounds can be dimeric or trimeric, other carboxylate salts form complexes, e. g. citrate and tartrate. Iron chloride is a mild oxidising agent, for example, it is capable of oxidising copper chloride to copper chloride. FeCl3 + CuCl → FeCl2 + CuCl2 It also reacts with iron to iron chloride,2 FeCl3 + Fe →3 FeCl2 Reducing agents such as hydrazine convert iron chloride to complexes of iron. Iron chloride is used in treatment and drinking water production. In this application, FeCl3 in slightly basic water reacts with the ion to form a floc of iron hydroxide, or more precisely formulated as FeO−
Iron(III) chloride
–
Iron(III) chloride
Iron(III) chloride
–
A brown, acidic solution of iron(III) chloride
Iron(III) chloride
–
Granulated iron(III) chloride hexahydrate
47.
Isomer
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An isomer is a molecule with the same molecular formula as another molecule, but with a different chemical structure. That is, isomers contain the number of atoms of each element. Isomers do not necessarily share similar properties, unless they also have the functional groups. There are two forms of isomerism, structural isomerism and stereoisomerism. In structural isomers, sometimes referred to as constitutional isomers, the atoms, Structural isomers have different IUPAC names and may or may not belong to the same functional group. For example, two position isomers would be 2-fluoropropane and 1-fluoropropane, illustrated on the side of the diagram above. In skeletal isomers the main chain is different between the two isomers. This type of isomerism is most identifiable in secondary and tertiary alcohol isomers, tautomers are structural isomers that spontaneously interconvert with each other, even when pure. They have different chemical properties and, as a consequence, distinct reactions characteristic to each form are observed, if the interconversion reaction is fast enough, tautomers cannot be isolated from each other. An example is when they differ by the position of a proton, such as in keto/enol tautomerism, there is, however, another isomer of C3H8O that has significantly different properties, methoxyethane. Unlike the isomers of propanol, methoxyethane has an oxygen connected to two carbons rather than to one carbon and one hydrogen. Methoxyethane is an ether, not an alcohol, because it lacks a hydroxyl group, propadiene and propyne are examples of isomers containing different bond types. Propadiene contains two double bonds, whereas propyne contains one triple bond, in stereoisomers the bond structure is the same, but the geometrical positioning of atoms and functional groups in space differs. This class includes enantiomers which are non-superposable mirror-images of each other, and diastereomers, enantiomers always contain chiral centers and diastereomers often do, but there are some diastereomers that neither are chiral nor contain chiral centers. Another type of isomer, conformational isomers, may be rotamers, diastereomers, for example, ortho- position-locked biphenyl systems have enantiomers. E/Z isomers, which have restricted rotation at a bond, are configurational isomers. They are classified as diastereomers, whether or not they contain any chiral centers, e/Z notation depicts absolute stereochemistry, which is an unambiguous descriptor based on CIP priorities. Cis–trans isomers are used to describe any molecules with restricted rotation in the molecule, for molecules with C=C double bonds, these descriptors describe relative stereochemistry only based on group bulkiness or principal carbon chain, and so can be ambiguous
Isomer
48.
Chlorotoluene
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Chlorotoluene is a group of three isomeric chemical compounds. They consist of a benzene ring with one chlorine atom. The isomers differ in the location of the chlorine, but have the chemical formula. All have very similar boiling points, although p-chlorotoluene has a higher melting point due to a more tightly-packed crystal structure. Benzyl chloride is an isomer, which has a chlorine substituted for one of the hydrogens of toluenes methyl group, CDC - NIOSH Pocket Guide to Chemical Hazards - o-Chlorotoluene
Chlorotoluene
–
Structure
49.
Potassium permanganate
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Potassium permanganate is an inorganic chemical compound and medication. As a medication it is used for cleaning wounds and dermatitis and it has the chemical formula KMnO4 and is a salt consisting of K+ and MnO−4 ions. It is an oxidizing agent. It dissolves in water to give intensely pink or purple solutions, in 2000, worldwide production was estimated at 30,000 tonnes. In this compound, manganese is in the +7 oxidation state and it is on the WHO Model List of Essential Medicines, the most important medications needed in a basic health system. The wholesale cost in the world is about 0.01 USD per gram of powder. In the United Kingdom a 400 milligram tablet costs the NHS roughly £0.51, almost all applications of potassium permanganate exploit its oxidizing properties. As a strong oxidant that does not generate toxic byproducts, KMnO4 has many niche uses, as an oxidant, potassium permanganate can act as an antiseptic. For example, dilute solutions are used to treat sores, disinfectant for the hands and treatment for mild pompholyx, dermatitis. Potassium permanganate is used extensively in the treatment industry. It is used as a chemical to remove iron and hydrogen sulfide from well water via a Manganese Greensand Filter. Pot-Perm is also obtainable at pool supply stores and is used additionally to treat waste water, historically it was used to disinfect drinking water and can turn the water pink. It currently finds application in the control of nuisance organisms such as zebra mussels in fresh water collection, aside from its use in water treatment, the other major application of KMnO4 is as a reagent for the synthesis of organic compounds. Significant amounts are required for the synthesis of ascorbic acid, chloramphenicol, saccharin, isonicotinic acid, potassium permanganate can be used to quantitatively determine the total oxidisable organic material in an aqueous sample. The value determined is known as the permanganate value, in analytical chemistry, a standardized aqueous solution of KMnO4 is sometimes used as an oxidizing titrant for redox titrations. In a related way, it is used as a reagent to determine the Kappa number of wood pulp, for the standardization of KMnO4 solutions, reduction by oxalic acid is often used. Aqueous, acidic solutions of KMnO4 are used to collect gaseous mercury in flue gas during stationary source emissions testing, in histology, potassium permanganate was used as a bleaching agent. Ethylene absorbents extend storage time of bananas even at high temperatures and this effect can be exploited by packing bananas in polyethylene together with potassium permanganate
Potassium permanganate
Potassium permanganate
–
Potassium permanganate
Potassium permanganate
–
A solution of KMnO 4 in water, in a
volumetric flask
50.
Chromyl chloride
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Chromyl chloride is a chemical compound with the formula CrO2Cl2. This compound is an opaque dark blood-red liquid at room temperature and pressure and it is tetrahedral, somewhat like SO2Cl2. CrO2Cl2 is similar to the most commonly encountered chromium derivative chromate, 2−, however, they differ in both oxidizing power and in physical properties, one is a liquid and the other forms salts. CrO2Cl2 is a molecular species. This means that in the liquid and solid forms, the individual CrO2Cl2 entities interact predominantly via van der Waals bonding, such weak bonding leads to low melting and boiling points, which is related to the fact that it is a distillable liquid. The diminished oxidizing power of 2− vs. CrO2Cl2 can be ascribed to its anionic nature, also, chloride is a poorer pi-donor ligand than is oxide. Chromyl chloride can be prepared by mixing potassium chromate or potassium dichromate with sodium chloride and treating this mix with concentrated sulfuric acid, the chromyl chloride test entails heating a sample suspected of containing chloride with potassium dichromate and concentrated sulfuric acid. If chloride is present, chromyl chloride is formed and red fumes of CrO2Cl2 are evident, if there is no chloride present, no red fumes are produced. No analogous compounds are formed with fluorides, bromides, iodides and cyanides, the test is related to the synthesis shown above, exposure of CrO42− to HCl. Depending on solvent, CrO2Cl2 oxidizes terminal alkenes to aldehydes, internal alkenes give alpha-chloroketones or related derivatives. It will also attack benzylic methyl groups to give aldehydes via the Étard reaction, apart from this it can also be used for testing the absence of nitrate ions. CrO2Cl2 is such a reagent that solvents must be chosen judiciously. Typical for other electrophilic chlorides, chlorocarbons are excellent solvents, especially dichloromethane As a further practical complication, CrO2Cl2 reacts with water to release hydrochloric acid and hexavalent chromium Acute, HCl can be acutely lethal. Exposure to chromyl chloride vapour irritates the respiratory system and severely irritates the eyes, ingestion would cause severe internal damage. Chronic, CrVI can produce chromosomal aberrations and is a human carcinogen via inhalation, frequent exposure of the skin to chromyl chloride may result in ulceration. Thus, CrO2Cl2 should be handled in a well ventilated area. CrO2Cl2 is so aggressive that its storage can be problematic as it attacks rubber, F. Freeman Chromyl Chloride in Encyclopedia of Reagents for Organic Synthesis 2004, J. Wiley & Sons, New York. CDC - NIOSH Pocket Guide to Chemical Hazards - Chromyl Chloride
Chromyl chloride
–
Chromyl chloride
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