1.
1,1,1,2-Tetrafluoroethane
–
It has the formula CH2FCF3 and a boiling point of −26.3 °C at atmospheric pressure. R-134a cylinders are colored light blue, attempts at phasing out its use as a refrigerant with substances that have lower global warming potentials, such as HFO-1234yf are underway. 1,1,1, 2-Tetrafluoroethane is a gas used primarily as a high-temperature refrigerant for domestic refrigeration. 1,1,1, 2-Tetrafluoroethane has also used to cool computers in some overclocking attempts. It is also used as a propellant for airsoft airguns. The gas is mixed with a silicon-based lubricant. It can also be used as a solvent in organic chemistry and it is used in the resistive plate chamber particle detectors in the Large Hadron Collider. It is also used for types of particle detectors, e. g. some cryogenic particle detectors. It can be used as an alternative to sulfur hexafluoride in magnesium smelting as a shielding gas,1,1,1, 2-tetrafluoroethane is also being considered as an alternative to sulfur hexafluoride as a dielectric gas. Its arc-quenching properties are poor, but its properties are fairly good. Recently,1,1,1, 2-tetrafluoroethane has been subject to use due to its contribution to climate change. It has a global warming potential of 1300, the Society of Automotive Engineers has proposed 1,1,1, 2-tetrafluoroethane to be best replaced by a new fluorochemical refrigerant HFO-1234yf in automobile air-conditioning systems. California may also prohibit the sale of canned 1,1,1, the ban has been lifted in Wisconsin in 2012. 1,1,1, 2-Tetrafluoroethane first appeared in the early 1990s as a replacement for dichlorodifluoromethane,1,1,1, 2-Tetrafluoroethane has been atmospherically modeled for its impact on depleting ozone and as a contributor to global warming. It has insignificant ozone depletion potential, significant global warming potential, because of its high GWP,1,1,1, 2-tetrafluoroethane has been banned from use in the European Union, starting with cars in 2011 and phasing out completely by 2017. Mixtures with air of the gas 1,1,1, 2-tetrafluoroethane are not flammable at atmospheric pressure, however, mixtures with high concentrations of air at elevated pressure and/or temperature can be ignited. Contact of 1,1,1, 2-tetrafluoroethane with flames or hot surfaces in excess of 250 °C may cause vapor decomposition and the emission of toxic gases including hydrogen fluoride and carbonyl halides. 1,1,1, 2-Tetrafluoroethane itself has an LD50 of 1,500 g/m3 in rats, making it relatively non-toxic and its gaseous form is denser than air and will displace air in the lungs
2.
Gas duster
–
Gas duster, also known as canned air or compressed air, is a product used for cleaning or dusting electronic equipment and other sensitive devices that cannot be cleaned using water. The products are most often a can that, when a trigger is pressed, despite the name canned air, the cans actually contain gases that are compressable into liquids. Air on the contrary, cannot be compressed into liquid at any pressure since the temperatures of air components are much beyond normal handling temperatures. Duster gases are such as 1, 1-difluoroethane,1,1, 1-trifluoroethane, hydrocarbons, like butane, were often used in the past, but their flammable nature forced manufacturers to use fluorocarbons. When inhaled, gas duster fumes may produce psychoactive effects and may be harmful to health, since gas dusters are one of the many inhalants that can be easily abused, many manufacturers have added a bittering agent to deter people from inhaling the product. Because of the name canned air, it was mistakenly believed that the can only contains normal air or contains a less harmful substance such as nitrous oxide. However, the actually used are denser than air, such as difluoroethane. When inhaled, the gas displaces the oxygen in the lungs and this type of inhalant abuse can cause a plethora of negative effects including brain and nerve damage, paralysis, serious injury, or death. The liquid, when released from the can, boils at a low temperature. This can cause mild to moderate frostbite on contact with skin, also, the can gets very cold during extended use, holding the can itself can result in cold burns. Since gas dusters are often contained in vessels, they are considered explosively volatile. Global warming, Difluoroethane, trifluoroethane, and completely non-flammable tetrafluoroethane are potent greenhouse gases, according to the Intergovernmental Panel on Climate Change, the global warming potential of HFC-152a, HFC-143a, and HFC-134a are 124,4470, and 1430, respectively. GWP refers to global warming effect in comparison to CO2 for unit mass and this is a separate issue from the global warming concern. Many gas dusters contain HFC-134a, which is used as a propellant and refrigerant. HFC-134a sold for those purposes is often sold at a higher unit price. Adapters have been built for such purposes, though in most cases, one example of this practice is the case of airsoft gas guns, which use HFC-134a as the compressed gas. Several vendors sell duster adapters for use with airsoft guns, though it is necessary to add a lubricant when using gas dusters to power airsoft guns, true air dusters using ordinary air are also available in the market. These typically have much shorter run times than a chemical duster, both hand pump and electric compressor models have been marketed
3.
Chemical compound
–
A chemical compound is an entity consisting of two or more atoms, at least two from different elements, which associate via chemical bonds. Many chemical compounds have a numerical identifier assigned by the Chemical Abstracts Service. For example, water is composed of two atoms bonded to one oxygen atom, the chemical formula is H2O. A compound can be converted to a different chemical composition by interaction with a chemical compound via a chemical reaction. In this process, bonds between atoms are broken in both of the compounds, and then bonds are reformed so that new associations are made between atoms. Schematically, this reaction could be described as AB + CD → AC + BD, where A, B, C, and D are each unique atoms, and AB, CD, AC, and BD are each unique compounds. A chemical element bonded to a chemical element is not a chemical compound since only one element. Examples are the diatomic hydrogen and the polyatomic molecule sulfur. Chemical compounds have a unique and defined chemical structure held together in a spatial arrangement by chemical bonds. Pure chemical elements are not considered chemical compounds, failing the two or more atom requirement, though they often consist of molecules composed of multiple atoms. There is varying and sometimes inconsistent nomenclature differentiating substances, which include truly non-stoichiometric examples, from chemical compounds, other compounds regarded as chemically identical may have varying amounts of heavy or light isotopes of the constituent elements, which changes the ratio of elements by mass slightly. Characteristic properties of compounds include that elements in a compound are present in a definite proportion, for example, the molecule of the compound water is composed of hydrogen and oxygen in a ratio of 2,1. In addition, compounds have a set of properties. The physical and chemical properties of compounds differ from those of their constituent elements, however, mixtures can be created by mechanical means alone, but a compound can be created only by a chemical reaction. Some mixtures are so combined that they have some properties similar to compounds. Other examples of compound-like mixtures include intermetallic compounds and solutions of metals in a liquid form of ammonia. Compounds may be described using formulas in various formats, for compounds that exist as molecules, the formula for the molecular unit is shown. For polymeric materials, such as minerals and many metal oxides, the elements in a chemical formula are normally listed in a specific order, called the Hill system
4.
Alkane
–
In organic chemistry, an alkane, or paraffin, is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a structure in which all the carbon-carbon bonds are single. Alkanes have the chemical formula CnH2n+2. The alkanes range in complexity from the simplest case of methane, CH4 where n =1, in an alkane, each carbon atom has 4 bonds, and each hydrogen atom is joined to one of the carbon atoms. The longest series of linked carbon atoms in a molecule is known as its skeleton or carbon backbone. The number of atoms may be thought of as the size of the alkane. One group of the alkanes are waxes, solids at standard ambient temperature and pressure. They can be viewed as molecular trees upon which can be hung the more functional groups of biological molecules. The alkanes have two main sources, petroleum and natural gas. Saturated hydrocarbons are hydrocarbons having only single covalent bonds between their carbons, according to the definition by IUPAC, the former two are alkanes, whereas the third group is called cycloalkanes. Saturated hydrocarbons can also combine any of the linear, cyclic and branching structures, the formula is CnH 2n−2k+2. Alkanes are the ones, corresponding to k =0. Alkanes with more than three carbon atoms can be arranged in different ways, forming structural isomers. The simplest isomer of an alkane is the one in which the atoms are arranged in a single chain with no branches. This isomer is called the n-isomer. However the chain of atoms may also be branched at one or more points. The number of possible isomers increases rapidly with the number of carbon atoms, for example, 3-methylhexane and its higher homologues are chiral due to their stereogenic center at carbon atom number 3. In addition to the alkane isomers, the chain of atoms may form one or more loops
5.
Halogen
–
The halogens or halogen elements are a group in the periodic table consisting of five chemically related elements, fluorine, chlorine, bromine, iodine, and astatine. The artificially created element 117 may also be a halogen, in the modern IUPAC nomenclature, this group is known as group 17. The symbol X is often used generically to refer to any halogen, when halogens react with metals they produce a wide range of salts, including calcium fluoride, sodium chloride, silver bromide and potassium iodide. The group of halogens is the periodic table group that contains elements in three of the four main states of matter at standard temperature and pressure. All of the halogens form acids when bonded to hydrogen, most halogens are typically produced from minerals or salts. The middle halogens, that is chlorine, bromine and iodine, are used as disinfectants. Organobromides are the most important class of flame retardants, elemental halogens are dangerously to potentially lethally toxic. The fluorine mineral fluorospar was known as early as 1529, early chemists realized that fluorine compounds contain an undiscovered element, but were unable to isolate it. In 1869, George Gore, an English chemist, ran a current of electricity through hydrofluoric acid and discovered fluorine, in 1886, Henri Moissan, a chemist in Paris, performed electrolysis on potassium bifluoride dissolved in waterless hydrofluoric acid, and successfully produced fluorine. Hydrochloric acid was known to alchemists and early chemists, However, elemental chlorine was not produced until 1774, when Carl Wilhelm Scheele heated hydrochloric acid with manganese dioxide. Scheele called the element dephlogisticated muriatic acid, which is how chlorine was known for 33 years, in 1807, Humphry Davy investigated chlorine and discovered that it is an actual element. Chlorine was used as a poison gas during World War I, bromine was discovered in the 1820s by Antoine-Jérôme Balard. Balard discovered bromine by passing gas through a sample of brine. He originally proposed the name muride for the new element, iodine was discovered by Bernard Courtois, who was using seaweed ash as part of a process for saltpeter manufacture. Courtois typically boiled the seaweed ash with water to generate potassium chloride, However, in 1811, Courtois added sulfuric acid to his process, and found that his process produced purple fumes that condensed into black crystals. Suspecting that these crystals were a new element, Courtois sent samples to other chemists for investigation, iodine was proven to be a new element by Joseph Gay-Lussac. In 1931, Fred Allison claimed to have discovered element 85 with a machine, and named the element Alabamine. In 1937, Jajendralal De claimed to have discovered element 85 in minerals, and called the element dakine, element 85, now named astatine, was produced successfully in 1940 by Dale R. Corson, K. R
6.
Halocarbon
–
Chlorine halocarbons are the most common and are called organochlorides. Many synthetic organic compounds such as polymers, and a few natural ones, contain halogen atoms. Organochlorides are the most common industrially used organohalides, although the other organohalides are used commonly in organic synthesis, except for extremely rare cases, organohalides are not produced biologically, but many pharmaceuticals are organohalides. Notably, many such as Prozac have trifluoromethyl groups. For information on inorganic chemistry, see halide. Halocarbons are typically classified in the ways as the similarly structured organic compounds that have hydrogen atoms occupying the molecular sites of the halogen atoms in halocarbons. The halogen atoms in molecules are often called substituents, as though those atoms had been substituted for hydrogen atoms. However halocarbons are prepared in ways that do not involve direct substitution of halogens for hydrogens. A few halocarbons are produced in massive amounts by microorganisms, for example, several million tons of methyl bromide are estimated to be produced by marine organisms annually. Most of the halocarbons encountered in everyday life – solvents, medicines, the first synthesis of halocarbons was achieved in the early 1800s. Production began accelerating when their useful properties as solvents and anesthetics were discovered, development of plastics and synthetic elastomers has led to greatly expanded scale of production. A substantial percentage of drugs are halocarbons, a large amount of the naturally occurring halocarbons are created by wood fire, dioxine for example, or volcanic activities. A second large source are marine algae which produce several chlorinated methane and ethane containing compounds, there are several thousand complex halocarbons known, produced mainly by marine species. Although chlorine compounds are the majority of the compounds, bromides, iodides and fluorides have also been found. These three representatives, thyroxine from humans, tyrian purple from snails and fluoroacetate from plants, also show that unrelated species use halocarbons for several purposes, organoiodine compounds, called organic iodides, are similar in structure to organochlorine and organobromine compounds, but the C-I bond is weaker. Many organic iodides are known, but few are of industrial importance. Iodide compounds are produced as nutritional supplements. The thyroxin hormones are essential for health, hence the usefulness of iodized salt
7.
Fire extinguisher
–
A fire extinguisher is an active fire protection device used to extinguish or control small fires, often in emergency situations. It is not intended for use on a fire, such as one which has reached the ceiling, endangers the user. Typically, a fire extinguisher consists of a cylindrical pressure vessel containing an agent which can be discharged to extinguish a fire. Fire extinguishers manufactured with non-cylindrical pressure vessels also exist, but are less common, in the United States, fire extinguishers in all buildings other than houses are generally required to be serviced and inspected by a fire protection service company at least annually. Some jurisdictions require more frequent service for fire extinguishers, the servicer places a tag on the extinguisher to indicate the type of service performed. There are two types of fire extinguishers, stored-pressure and cartridge-operated. In stored pressure units, the expellant is stored in the chamber as the firefighting agent itself. Depending on the agent used, different propellants are used, with dry chemical extinguishers, nitrogen is typically used, water and foam extinguishers typically use air. Stored pressure fire extinguishers are the most common type, Cartridge-operated extinguishers contain the expellant gas in a separate cartridge that is punctured prior to discharge, exposing the propellant to the extinguishing agent. This type is not as common, used primarily in areas such as industrial facilities and they have the advantage of simple and prompt recharge, allowing an operator to discharge the extinguisher, recharge it, and return to the fire in a reasonable amount of time. Unlike stored pressure types, these extinguishers use compressed carbon dioxide instead of nitrogen, although nitrogen cartridges are used on low temperature models. Cartridge operated extinguishers are available in dry chemical and dry powder types in the U. S. and in water, wetting agent, foam, dry chemical, Fire extinguishers are further divided into handheld and cart-mounted. Handheld extinguishers weigh from 0.5 to 14 kilograms, and are hence, cart-mounted units typically weigh more than 23 kilograms. These wheeled models are most commonly found at sites, airport runways, heliports, as well as docks. The first fire extinguisher of which there is any record was patented in England in 1723 by Ambrose Godfrey and it consisted of a cask of fire-extinguishing liquid containing a pewter chamber of gunpowder. This was connected with a system of fuses which were ignited, exploding the gunpowder and this device was probably used to a limited extent, as Bradleys Weekly Messenger for November 7,1729, refers to its efficiency in stopping a fire in London. The modern fire extinguisher was invented by British Captain George William Manby in 1818, the soda-acid extinguisher was first patented in 1866 by Francois Carlier of France, which mixed a solution of water and sodium bicarbonate with tartaric acid, producing the propellant CO2 gas. A soda-acid extinguisher was patented in the U. S. in 1881 by Almon M. Granger and his extinguisher used the reaction between sodium bicarbonate solution and sulfuric acid to expel pressurized water onto a fire
8.
Refrigerant
–
A refrigerant is a substance or mixture, usually a fluid, used in a heat pump and refrigeration cycle. In most cycles it undergoes phase transitions from a liquid to a gas, many working fluids have been used for such purposes. Fluorocarbons, especially chlorofluorocarbons, became commonplace in the 20th century, other common refrigerants used in various applications are ammonia, sulfur dioxide, and non-halogenated hydrocarbons such as propane. The ideal refrigerant would have favorable properties, be noncorrosive to mechanical components. It would not cause ozone depletion or climate change, since different fluids have the desired traits in different degree, choice is a matter of trade-off. Since boiling point and gas density are affected by pressure, refrigerants may be more suitable for a particular application by choice of operating pressures. In order from the highest to the lowest potential of ozone depletion are Bromochlorofluorocarbon, though HFC and PFC are non-ozone depleting, many have global warming potentials that are thousands of times greater than CO2. Some other refrigerants such as propane and ammonia are not inert, new refrigerants were developed in the early 21st century that are safer for the environment, but their application has been held up due to concerns over toxicity and flammability. Early mechanical refrigeration systems employed sulfur dioxide, methyl chloride and ammonia, being toxic, sulfur dioxide and methyl chloride rapidly disappeared from the market with the introduction of CFCs. Occasionally, one may encounter older machines with methyl formate, chloromethane, chlorofluorocarbons were little used for refrigeration until better synthesis methods, developed in the 1950s, reduced their cost. Their domination of the market was called into question in the 1980s by concerns about depletion of the ozone layer and they are currently subject to prohibition discussions on account of their harmful effect on the climate. In 1997, FCs and HFCs were included in the Kyoto Protocol to the Framework Convention on Climate Change, in 2006, the EU adopted a Regulation on fluorinated greenhouse gases, which makes stipulations regarding the use of FCs and HFCs with the intention of reducing their emissions. The provisions do not affect climate-neutral refrigerants, refrigerants such as ammonia, carbon dioxide and non-halogenated hydrocarbons do not deplete the ozone layer and have no or only a low global warming potential. They are used in air-conditioning systems for buildings, in sport and leisure facilities, in the industry, in the automotive industry. In these settings their toxicity is less a concern than in home equipment, emissions from automobile air conditioning are a growing concern because of their impact on climate change. From 2011 on, the European Union will phase out refrigerants with a global warming potential of more than 150 in automotive air conditioning and this will ban potent greenhouse gases such as the refrigerant HFC-134a —which has a GWP of 1410—to promote safe and energy-efficient refrigerants. One of the most promising alternatives is CO2, carbon dioxide is non-flammable, non-ozone depleting, has a global warming potential of 1. R-744 can be used as a fluid in climate control systems for cars, residential air conditioning, hot water pumps, commercial refrigeration
9.
Pharmaceutical
–
A pharmaceutical drug is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy is an important part of the field and relies on the science of pharmacology for continual advancement. Drugs are classified in various ways, one of the key divisions is by level of control, which distinguishes prescription drugs from over-the-counter drugs. Other ways to classify medicines are by mode of action, route of administration, biological system affected, an elaborate and widely used classification system is the Anatomical Therapeutic Chemical Classification System. The World Health Organization keeps a list of essential medicines, Drug discovery and drug development are complex and expensive endeavors undertaken by pharmaceutical companies, academic scientists, and governments. Governments generally regulate what drugs can be marketed, how drugs are marketed, controversies have arisen over drug pricing and disposal of used drugs. In the US, a drug is, A substance recognized by an official pharmacopoeia or formulary, a substance intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease. A substance intended to affect the structure or any function of the body, a substance intended for use as a component of a medicine but not a device or a component, part or accessory of a device. Pharmaceutical or a drug is classified on the basis of their origin, Drug from natural origin, Herbal or plant or mineral origin, some drug substances are of marine origin. Drug from chemical as well as origin, Derived from partial herbal and partial chemical synthesis Chemical. Drug derived from animal origin, For example, hormones, Drug derived from microbial origin, Antibiotics Drug derived by biotechnology genetic-engineering, hybridoma technique for example Drug derived from radioactive substances. An elaborate and widely used system is the Anatomical Therapeutic Chemical Classification System. The World Health Organization keeps a list of essential medicines, the main classes of painkillers are NSAIDs, opioids and Local anesthetics. For consciousness Some anesthetics include Benzodiazepines and Barbiturates, the main categories of drugs for musculoskeletal disorders are, NSAIDs, muscle relaxants, neuromuscular drugs, and anticholinesterases. Euthanasia is not permitted by law in countries, and consequently medicines will not be licensed for this use in those countries. Administration is the process by which a patient takes a medicine, there are three major categories of drug administration, enteral, parenteral, and other. It can be performed in various forms such as pills, tablets. There are many variations in the routes of administration, including intravenous and they can be administered all at once as a bolus, at frequent intervals or continuously
10.
Pollutant
–
A pollutant is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. A pollutant may cause long- or short-term damage by changing the rate of plant or animal species, or by interfering with human amenities, comfort, health. Some pollutants are biodegradable and therefore will not persist in the environment in the long term, however the degradation products of some pollutants are themselves polluting such as the products DDE and DDD produced from degradation of DDT. Pollutants, towards which the environment has little or no absorptive capacity are called stock pollutants, stock pollutants accumulate in the environment over time. The damage they cause increases as more pollutant is emitted, stock pollutants can create a burden for future generations, by passing on damage that persists well after the ‘benefits received from incurring that damage, have been forgotten. Fund pollutants are those for which the environment has some absorptive capacity, fund pollutants do not cause damage to the environment unless the emission rate exceeds the receiving environments absorptive capacity. Fund pollutants are not destroyed, but rather converted into less harmful substances and it also encompasses ecological light pollution which describes the effect of artificial light on individual organisms and on the structure of ecosystems as a whole. Pollutants can also be defined by their zones of influence, both horizontally and vertically, the horizontal zone refers to the area that is damaged by a pollutant. Local pollutants cause damage near the emission source, regional pollutants cause damage further from the emission source. The vertical zone is referred to whether the damage is ground-level or atmospheric, surface pollutants cause damage by concentrations of the pollutant accumulating near the Earths surface Global pollutants cause damage by concentrations in the atmosphere. Pollutants can cross borders and therefore international regulations are needed for their control. The Stockholm Convention on Persistent Organic Pollutants, which entered force in 2004, is an international legally binding agreement for the control of persistent organic pollutants. Pollutant Release and Transfer Registers are systems to collect and disseminate information on releases and transfers of toxic chemicals from industrial. The National Emissions Standards for Hazardous Air Pollutants are additional emission standards that are set by EPA for toxic air pollutants, under the Clean Water Act, EPA promulgated national standards for municipal sewage treatment plants, also called publicly owned treatment works, in the Secondary Treatment Regulation. National standards for industrial dischargers are called Effluent guidelines and New Source Performance Standards, in addition, the Act requires states to publish water quality standards for individual water bodies to provide additional protection where the national standards are insufficient. The Resource Conservation and Recovery Act regulates the management, transport and disposal of solid waste, hazardous waste. A tank or piping network that has at least 10 percent of its volume underground is known as a storage tank. They often store substances such as petroleum, that are harmful to the environment should it become contaminated
11.
Chlorofluorocarbon
–
A chlorofluorocarbon is an organic compound that contains only carbon, chlorine, and fluorine, produced as volatile derivative of methane, ethane, and propane. They are also known by the DuPont brand name Freon. The most common representative is dichlorodifluoromethane, many CFCs have been widely used as refrigerants, propellants, and solvents. As in simpler alkanes, carbon in the CFCs bonds with tetrahedral symmetry, because the fluorine and chlorine atoms differ greatly in size and effective charge from hydrogen and from each other, the methane-derived CFCs deviate from perfect tetrahedral symmetry. The physical properties of CFCs and HCFCs are tunable by changes in the number, in general they are volatile, but less so than their parent alkanes. The decreased volatility is attributed to the molecular polarity induced by the halides, thus, methane boils at −161 °C whereas the fluoromethanes boil between −51.7 and −128 °C. The CFCs have still higher boiling points because the chloride is even more polarizable than fluoride, because of their polarity, the CFCs are useful solvents, and their boiling points make them suitable as refrigerants. The densities of CFCs are higher than their corresponding alkanes, in general the density of these compounds correlates with the number of chlorides. CFCs and HCFCs are usually produced by halogen exchange starting from chlorinated methanes and ethanes, the chlorine atom, written often as Cl. behaves very differently from the chlorine molecule. The radical Cl. is long-lived in the atmosphere, where it catalyzes the conversion of ozone into O2. Ozone absorbs UV-B radiation, so its depletion allows more of high energy radiation to reach the Earths surface. Bromine atoms are more efficient catalysts, hence brominated CFCs are also regulated. Applications exploit the low toxicity, low reactivity, and low flammability of the CFCs and HCFCs, every permutation of fluorine, chlorine, and hydrogen based on methane and ethane has been examined and most have been commercialized. Furthermore, many examples are known for higher numbers of carbon as well as related compounds containing bromine, uses include refrigerants, blowing agents, propellants in medicinal applications, and degreasing solvents. Billions of kilograms of chlorodifluoromethane are produced annually as precursor to tetrafluoroethylene, chlorofluorocarbons, when derived from methane and ethane these compounds have the formulae CClmF4−m and C2ClmF6−m, where m is nonzero. Hydrofluorocarbons, when derived from methane, ethane, propane, and butane, these compounds have the respective formulae CFmH4−m, C2FmH6−m, C3FmH8−m, and C4FmH10−m, a numbering system is used for fluorinated alkanes, prefixed with Freon-, R-, CFC-, and HCFC-. The rightmost value indicates the number of atoms, the next value to the left is the number of hydrogen atoms plus 1. Thus, Freon-12 indicates a methane derivative containing two fluorine atoms and no hydrogen, another, easier equation that can be applied to get the correct molecular formula of the CFC/R/Freon class compounds is this to take the numbering and add 90 to it
12.
Ozone depletion
–
The latter phenomenon is referred to as the ozone hole. In addition to these well-known stratospheric phenomena, there are also springtime polar tropospheric ozone depletion events, the details of polar ozone hole formation differ from that of mid-latitude thinning but the most important process in both is catalytic destruction of ozone by atomic halogens. The main source of these atoms in the stratosphere is photodissociation of man-made halocarbon refrigerants, solvents, propellants. These compounds are transported into the stratosphere by winds after being emitted at the surface, both types of ozone depletion were observed to increase as emissions of halocarbons increased. CFCs and other substances are referred to as ozone-depleting substances. Three forms of oxygen are involved in the cycle, oxygen atoms, oxygen gas. Ozone is formed in the stratosphere when oxygen molecules photodissociate after intaking an ultraviolet photon whose wavelength is shorter than 240 nm and this converts a single O2 into two atomic oxygen radicals. The atomic oxygen radicals then combine with separate O2 molecules to create two O3 molecules and these ozone molecules absorb ultraviolet light between 310 and 200 nm, following which ozone splits into a molecule of O2 and an oxygen atom. The oxygen atom then joins up with a molecule to regenerate ozone. This is a process that terminates when an oxygen atom recombines with an ozone molecule to make two O2 molecules. 2 O3 →3 O2 The overall amount of ozone in the stratosphere is determined by a balance between production and recombination. Ozone can be destroyed by a number of free radical catalysts, the dot is a common notation to indicate that all of these species have an unpaired electron and are thus extremely reactive. Cl and Br atoms destroy ozone molecules through a variety of catalytic cycles, in the simplest example of such a cycle, a chlorine atom reacts with an ozone molecule, taking an oxygen atom to form chlorine monoxide and leaving an oxygen molecule. The ClO can react with a molecule of ozone, releasing the chlorine atom. More complicated mechanisms have been discovered that lead to destruction in the lower stratosphere as well. On a per atom basis, bromine is more efficient than chlorine at destroying ozone. As a result, both chlorine and bromine contribute significantly to overall ozone depletion, Laboratory studies have shown that fluorine and iodine atoms participate in analogous catalytic cycles. On average, a chlorine atom is able to react with 100,000 ozone molecules before it is removed from the catalytic cycle
13.
Ozone layer
–
The ozone layer or ozone shield is a region of Earths stratosphere that absorbs most of the Suns ultraviolet radiation. It contains high concentrations of ozone in relation to parts of the atmosphere. The ozone layer contains less than 10 parts per million of ozone, the ozone layer is mainly found in the lower portion of the stratosphere, from approximately 20 to 30 kilometres above Earth, although its thickness varies seasonally and geographically. The ozone layer was discovered in 1913 by the French physicists Charles Fabry and it was deduced that the missing radiation was being absorbed by something in the atmosphere. Eventually the spectrum of the radiation was matched to only one known chemical. Its properties were explored in detail by the British meteorologist G. M. B, Dobson, who developed a simple spectrophotometer that could be used to measure stratospheric ozone from the ground. Between 1928 and 1958, Dobson established a network of ozone monitoring stations. The Dobson unit, a convenient measure of the amount of overhead, is named in his honor. The ozone layer absorbs 97 to 99 percent of the Suns medium-frequency ultraviolet light, the United Nations General Assembly has designated September 16 as the International Day for the Preservation of the Ozone Layer. Venus also has an ozone layer at an altitude of 100 kilometers from the planets surface. The photochemical mechanisms that give rise to the layer were discovered by the British physicist Sydney Chapman in 1930. The ozone molecule is unstable and when light hits ozone it splits into a molecule of O2 and an individual atom of oxygen. Chemically, this can be described as, O2 + ℎνuv → 2O O + O2 ↔ O3 About 90 percent of the ozone in the atmosphere is contained in the stratosphere. Ozone concentrations are greatest between about 20 and 40 kilometres, where they range from about 2 to 8 parts per million, if all of the ozone were compressed to the pressure of the air at sea level, it would be only 3 millimetres thick. Although the concentration of the ozone in the layer is very small. Extremely short or vacuum UV is screened out by nitrogen, UV radiation capable of penetrating nitrogen is divided into three categories, based on its wavelength, these are referred to as UV-A, UV-B, and UV-C. UV-C, which is harmful to all living things, is entirely screened out by a combination of dioxygen. Nevertheless, some UV-B, particularly at its longest wavelengths, reaches the surface, Ozone is transparent to most UV-A, so most of this longer-wavelength UV radiation reaches the surface, and it constitutes most of the UV reaching the Earth
14.
Greenhouse gas
–
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the cause of the greenhouse effect. The primary greenhouse gases in Earths atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, without greenhouse gases, the average temperature of Earths surface would be about −18 °C, rather than the present average of 15 °C. In the Solar System, the atmospheres of Venus, Mars, human activities since the beginning of the Industrial Revolution have produced a 40% increase in the atmospheric concentration of carbon dioxide, from 280 ppm in 1750 to 400 ppm in 2015. This increase has occurred despite the uptake of a portion of the emissions by various natural sinks involved in the carbon cycle. Anthropogenic carbon dioxide emissions come from combustion of fuels, principally coal, oil. Greenhouse gases are those that absorb and emit infrared radiation in the range emitted by Earth. The proportion of an emission remaining in the atmosphere after a time is the airborne fraction. The annual airborne fraction is the ratio of the increase in a given year to that years total emissions. Over the last 50 years the annual airborne fraction for CO2 has been increasing at 0.25 ±0. 21%/year, therefore, they do not contribute significantly to the greenhouse effect and usually are omitted when discussing greenhouse gases. Some gases have indirect radiative effects and this happens in two main ways. One way is that when they break down in the atmosphere they produce another greenhouse gas, for example, methane and carbon monoxide are oxidized to give carbon dioxide. Oxidation of CO to CO2 directly produces an increase in radiative forcing although the reason is subtle. The peak of the thermal IR emission from Earths surface is close to a strong vibrational absorption band of CO2. On the other hand, the single CO vibrational band only absorbs IR at much higher frequencies, where the ~300 K thermal emission of the surface is at least a factor of ten lower. Oxidation of methane to CO2, which requires reactions with the OH radical, produces a reduction, since CO2 is a weaker greenhouse gas than methane. As described below this is not the story, since the oxidations of CO. In any case, the calculation of the radiative effect needs to include both the direct and indirect forcing
15.
Halomethane
–
Halomethane compounds are derivatives of methane with one or more of the hydrogen atoms replaced with halogen atoms. Halomethanes are both naturally occurring, especially in environments, and man-made, most notably as refrigerants, solvents, propellants. Like methane itself, halomethanes are tetrahedral molecules, the halogen atoms differ greatly in size and charge from hydrogen and from each other. Consequently, the various halomethanes deviate from the tetrahedral symmetry of methane. The physical properties of depend on the number and identity of the halogen atoms in the compound. In general, halomethanes are volatile but less so than methane because of the polarizability of the halides, the polarizability of the halides and the polarity of the molecules makes them useful as solvents. The halomethanes are far less flammable than methane, broadly speaking, reactivity of the compounds is greatest for the iodides and lowest for the fluorides. The halomethanes are produced on a scale from abundant precursors, i. e. natural gas or methanol. They are usually prepared by one of three methods, free radical chlorination of methane, CH4 + Cl2 → CH3Cl + HCl This method is useful for the production of CH4−xClx. The main problems with this method are that it cogenerates HCl, using CH4 in large excess generates primarily CH3Cl and using Cl2 in large excess generates primarily CCl4, but mixtures of other products will still be present. This method is used for the production of the mono-chloride, -bromide, and -iodide. CH3OH + HCl → CH3Cl + H2O4 CH3OH +3 Br2 + S →4 CH3Br + H2SO4 +2 HBr 3 CH3OH +3 I2 + P →3 CH3I + HPO2 +3 HI Halogen exchange. The method is used to produce fluorinated derivatives from the chlorides. CH4 + ClOH → CH3Cl + H2O Reaction of methanol with hypochlorous acid, CH3OH + ClOH → CH3Cl + H2O2 Traces of halomethanes in the atmosphere arise through the introduction of other non-natural, industrial materials. Many marine organisms biosynthesize halomethanes, especially bromine-containing compounds, small amounts of chloromethanes arise from the interaction of chlorine sources with various carbon compounds. The biosyntheses of these halomethanes are catalyzed by the chloroperoxidase and bromoperoxidase enzymes, an idealized equation is, CH4 + Cl− + 1/2 O2 → CH3Cl + OH− Halons are usually defined as hydrocarbons where the hydrogen atoms have been replaced by bromine, along with other halogens. They are referred to by a system of code numbers similar to the used for freons. The first digit specifies the number of atoms in the molecule, the second is the number of fluorine atoms, the third is the chlorine atoms
16.
Chloroethane
–
It is a colorless, flammable gas or refrigerated liquid with a faintly sweet odor. Some chloroethane is generated as a byproduct of polyvinyl chloride production, should demand for chloroethane continue to fall to the point where making it for its own sake is not economical, this may become the leading source of the chemical. Beginning in 1922 and continuing through most of the 20th century, the use of chloroethane was to produce tetraethyllead. TEL has been or is being phased out in most of the world. It also reacts with metal to give ethylaluminium sesquichloride, a precursor to polymers. Like other chlorinated hydrocarbons, chloroethane has been used as a refrigerant, an aerosol propellant, an anesthetic. For a time it was used as a chemical in the aluminium chloride catalyzed process to produce ethylbenzene. At present though, it is not widely used in any of these roles, the only remaining industrially important use of chloroethane is in treating cellulose to make ethylcellulose, a thickening agent and binder in paints, cosmetics, and similar products. Chloroethane is supplied as a liquid in a spray bottle propelled by its own vapor pressure and it acts as a mild topical anesthetic by its chilling effect when sprayed on skin, such as when removing splinters in a clinical setting. The heat absorbed by the liquid on tissues produces a deep and rapid chill. The vapor is flammable and narcotic, which requires care, similar to poppers, ethyl chloride is used as an inhalant during sexual activity, primarily by gay men. A small amount of the substance is placed on the tooth using a cotton wad. Chloroethanes low boiling point creates a chilling effect. If the tooth is still alive this should be sensed by the patient as mild discomfort that subsides when the wad is removed, monochloroethane is the least toxic of the chloroethanes. Like other chlorinated hydrocarbons, it is a nervous system depressant. People breathing its vapors at less than 1% concentration in air usually experience no symptoms, at concentrations of 3% to 5%, victims usually exhibit symptoms similar to those of alcohol intoxication. If exposed to higher than 6% to 8% victims often exhibit shallow breathing, loss of consciousnesses. They can be aroused with physical contact or loud noise, at this point removal from the area of exposure is advised to restore consciousness
17.
Hydrohalogenation
–
A hydrohalogenation reaction is the electrophilic addition of hydrohalic acids like hydrogen chloride or hydrogen bromide to alkenes to yield the corresponding haloalkanes. This is due to the abstraction of an atom by the alkene from the acid to form the most stable carbocation. A simple example of a hydrochlorination is that of indene with hydrochloric acid gas, In the presence of peroxides and this is because the reaction proceeds through the most stable carbon radical intermediate instead of a carbocation. The mechanism for this reaction is similar to a reaction such as free radical halogenation in which the peroxide promotes the formation of the bromide radical. However, this process is restricted to addition of HBr, no other hydrogen halide behaves in the manner described above, this can be explained by a survey of the different hydrohalic acids, HF, HCl, and HI. The hydrogen-fluorine bond is too strong and therefore no fluorine radicals can be generated in the propagation step. Hydrogen chloride will react in a manner that is so slow that it is essentially synthetically useless and this is because the hydrogen-chlorine bond is strong and thus the second step of the reaction would be extremely slow due to the heat required. Due to the weakness of the carbon-iodine bond necessary to complete the first step of the propagation phase, with Michael acceptors the addition is also anti-Markovnikov because now a nucleophilic X− reacts in a nucleophilic conjugate addition for example in the reaction of HCl with acrolein. Recent research has found that adding silica gel or alumina to H-Cl in dichloromethane increases the rate of making it an easy one to carry out
18.
Alcohol
–
In chemistry, an alcohol is any organic compound in which the hydroxyl functional group is bound to a saturated carbon atom. The term alcohol originally referred to the alcohol ethanol, the predominant alcohol in alcoholic beverages. The suffix -ol in non-systematic names also typically indicates that the substance includes a functional group and, so. But many substances, particularly sugars contain hydroxyl functional groups without using the suffix, an important class of alcohols, of which methanol and ethanol are the simplest members is the saturated straight chain alcohols, the general formula for which is CnH2n+1OH. The word alcohol is from the Arabic kohl, a used as an eyeliner. Al- is the Arabic definite article, equivalent to the in English, alcohol was originally used for the very fine powder produced by the sublimation of the natural mineral stibnite to form antimony trisulfide Sb 2S3, hence the essence or spirit of this substance. It was used as an antiseptic, eyeliner, and cosmetic, the meaning of alcohol was extended to distilled substances in general, and then narrowed to ethanol, when spirits as a synonym for hard liquor. Bartholomew Traheron, in his 1543 translation of John of Vigo, Vigo wrote, the barbarous auctours use alcohol, or alcofoll, for moost fine poudre. The 1657 Lexicon Chymicum, by William Johnson glosses the word as antimonium sive stibium, by extension, the word came to refer to any fluid obtained by distillation, including alcohol of wine, the distilled essence of wine. Libavius in Alchymia refers to vini alcohol vel vinum alcalisatum, Johnson glosses alcohol vini as quando omnis superfluitas vini a vino separatur, ita ut accensum ardeat donec totum consumatur, nihilque fæcum aut phlegmatis in fundo remaneat. The words meaning became restricted to spirit of wine in the 18th century and was extended to the class of substances so-called as alcohols in modern chemistry after 1850, the term ethanol was invented 1892, based on combining the word ethane with ol the last part of alcohol. In the IUPAC system, in naming simple alcohols, the name of the alkane chain loses the terminal e and adds ol, e. g. as in methanol and ethanol. When necessary, the position of the group is indicated by a number between the alkane name and the ol, propan-1-ol for CH 3CH 2CH 2OH, propan-2-ol for CH 3CHCH3. If a higher priority group is present, then the prefix hydroxy is used, in other less formal contexts, an alcohol is often called with the name of the corresponding alkyl group followed by the word alcohol, e. g. methyl alcohol, ethyl alcohol. Propyl alcohol may be n-propyl alcohol or isopropyl alcohol, depending on whether the group is bonded to the end or middle carbon on the straight propane chain. As described under systematic naming, if another group on the molecule takes priority, Alcohols are then classified into primary, secondary, and tertiary, based upon the number of carbon atoms connected to the carbon atom that bears the hydroxyl functional group. The primary alcohols have general formulas RCH2OH, the simplest primary alcohol is methanol, for which R=H, and the next is ethanol, for which R=CH3, the methyl group. Secondary alcohols are those of the form RRCHOH, the simplest of which is 2-propanol, for the tertiary alcohols the general form is RRRCOH
19.
Fluoroacetic acid
–
Fluoroacetic acid is a chemical compound with formula CH2FCOOH. The sodium salt, sodium fluoroacetate, is used as a pesticide and it inhibits the aconitase step of the citric acid cycle. Fluoroacetate occurs naturally in at least 40 plants in Australia, Brazil and it was first identified in Dichapetalum cymosum, commonly known as gifblaar or poison leaf, by Marais in 1944. As early as 1904, colonists in Sierra Leone used extracts of Chailletia toxicaria, several native Australian plant genera contain the toxin, including, Gastrolobium, Gompholobium, Oxylobium, Nemcia, and Acacia. Gastrolobium is a genus of flowering plants in the family Fabaceae, there are over 100 species in this genus, and all but two are native to the south west region of Western Australia, where they are known as poison peas. Gastrolobium growing in south western Australia are unique in their ability to concentrate fluoroacetate from low-fluorine soils, similarly, after bushfires in north-western Queensland, cattlemen have to move livestock before the poisonous Gastrolobium grandiflorum emerges from the ashes
20.
Carbon
–
Carbon is a chemical element with symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds, three isotopes occur naturally, 12C and 13C being stable, while 14C is a radioactive isotope, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity, Carbon is the 15th most abundant element in the Earths crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is the second most abundant element in the body by mass after oxygen. The atoms of carbon can bond together in different ways, termed allotropes of carbon, the best known are graphite, diamond, and amorphous carbon. The physical properties of carbon vary widely with the allotropic form, for example, graphite is opaque and black while diamond is highly transparent. Graphite is soft enough to form a streak on paper, while diamond is the hardest naturally occurring material known, graphite is a good electrical conductor while diamond has a low electrical conductivity. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal conductivities of all known materials, all carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form. They are chemically resistant and require high temperature to react even with oxygen, the most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and transition metal carbonyl complexes. The largest sources of carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil. For this reason, carbon has often referred to as the king of the elements. The allotropes of carbon graphite, one of the softest known substances, and diamond. It bonds readily with other small atoms including other carbon atoms, Carbon is known to form almost ten million different compounds, a large majority of all chemical compounds. Carbon also has the highest sublimation point of all elements, although thermodynamically prone to oxidation, carbon resists oxidation more effectively than elements such as iron and copper that are weaker reducing agents at room temperature. Carbon is the element, with a ground-state electron configuration of 1s22s22p2. Its first four ionisation energies,1086.5,2352.6,4620.5 and 6222.7 kJ/mol, are higher than those of the heavier group 14 elements. Carbons covalent radii are normally taken as 77.2 pm,66.7 pm and 60.3 pm, although these may vary depending on coordination number, in general, covalent radius decreases with lower coordination number and higher bond order. Carbon compounds form the basis of all life on Earth
21.
Fluorine
–
Fluorine is a chemical element with symbol F and atomic number 9. It is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions, as the most electronegative element, it is extremely reactive, almost all other elements, including some noble gases, form compounds with fluorine. Among the elements, fluorine ranks 24th in universal abundance and 13th in terrestrial abundance, proposed as an element in 1810, fluorine proved difficult and dangerous to separate from its compounds, and several early experimenters died or sustained injuries from their attempts. Only in 1886 did French chemist Henri Moissan isolate elemental fluorine using low-temperature electrolysis, industrial production of fluorine gas for uranium enrichment, its largest application, began during the Manhattan Project in World War II. Owing to the expense of refining pure fluorine, most commercial applications use fluorine compounds, the rest of the fluorite is converted into corrosive hydrogen fluoride en route to various organic fluorides, or into cryolite which plays a key role in aluminium refining. Organic fluorides have very high chemical and thermal stability, their uses are as refrigerants, electrical insulation and cookware. Pharmaceuticals such as atorvastatin and fluoxetine also contain fluorine, and the fluoride ion inhibits dental cavities, global fluorochemical sales amount to more than US$15 billion a year. Fluorocarbon gases are generally greenhouse gases with global-warming potentials 100 to 20,000 times that of carbon dioxide, organofluorine compounds persist in the environment due to the strength of the carbon–fluorine bond. Fluorine has no metabolic role in mammals, a few plants synthesize organofluorine poisons that deter herbivores. Fluorine atoms have nine electrons, one fewer than neon, and electron configuration 1s22s22p5, the outer electrons are ineffective at nuclear shielding, and experience a high effective nuclear charge of 9 −2 =7, this affects the atoms physical properties. Fluorines first ionization energy is third-highest among all elements, behind helium and neon and it also has a high electron affinity, second only to chlorine, and tends to capture an electron to become isoelectronic with the noble gas neon, it has the highest electronegativity of any element. Fluorine atoms have a small covalent radius of around 60 picometers, similar to those of its period neighbors oxygen, conversely, bonds to other atoms are very strong because of fluorines high electronegativity. Unreactive substances like powdered steel, glass fragments, and asbestos fibers react quickly with cold fluorine gas, wood, reactions of elemental fluorine with metals require varying conditions. Some solid nonmetals react vigorously in liquid air temperature fluorine, hydrogen sulfide and sulfur dioxide combine readily with fluorine, the latter sometimes explosively, sulfuric acid exhibits much less activity, requiring elevated temperatures. Hydrogen, like some of the metals, reacts explosively with fluorine. Carbon, as black, reacts at room temperature to yield fluoromethane. Graphite combines with fluorine above 400 °C to produce non-stoichiometric carbon monofluoride, higher temperatures generate gaseous fluorocarbons, heavier halogens react readily with fluorine as does the noble gas radon, of the other noble gases, only xenon and krypton react, and only under special conditions. At room temperature, fluorine is a gas of diatomic molecules and it has a characteristic pungent odor detectable at 20 ppb
22.
Chlorine
–
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
23.
Bromine
–
Bromine is a chemical element with symbol Br and atomic number 35. It is the third-lightest halogen, and is a fuming red-brown liquid at room temperature that readily to form a similarly coloured gas. Its properties are intermediate between those of chlorine and iodine. Isolated independently by two chemists, Carl Jacob Löwig and Antoine Jérôme Balard, its name was derived from the Ancient Greek βρῶμος stench, referencing its sharp and disagreeable smell. Elemental bromine is very reactive and thus does not occur free in nature, while it is rather rare in the Earths crust, the high solubility of the bromide ion has caused its accumulation in the oceans. Commercially the element is easily extracted from brine pools, mostly in the United States, Israel, the mass of bromine in the oceans is about one three-hundredth of that of chlorine. At high temperatures, organobromine compounds readily convert to free bromine atoms and this effect makes organobromine compounds useful as fire retardants and more than half the bromine produced worldwide each year is put to this purpose. Unfortunately, the same property causes sunlight to convert volatile organobromine compounds to free bromine atoms in the atmosphere, as a result, many organobromide compounds—such as the pesticide methyl bromide—are no longer used. Bromine compounds are used in well drilling fluids, in photographic film. Bromine has sometimes been considered to be essential in humans, but with the support of only limited circumstantial evidence. As a pharmaceutical, the bromide ion has inhibitory effects on the central nervous system. They retain niche uses as antiepileptics, bromine was discovered independently by two chemists, Carl Jacob Löwig and Antoine Balard, in 1825 and 1826, respectively. Löwig isolated bromine from a water spring from his hometown Bad Kreuznach in 1825. Löwig used a solution of the mineral salt saturated with chlorine, after evaporation of the ether a brown liquid remained. With this liquid as a sample for his work he applied for a position in the laboratory of Leopold Gmelin in Heidelberg, the publication of the results was delayed and Balard published his results first. Balard found bromine chemicals in the ash of seaweed from the marshes of Montpellier. The seaweed was used to produce iodine, but also contained bromine, Balard distilled the bromine from a solution of seaweed ash saturated with chlorine. In his publication, Balard states that he changed the name from muride to brôme on the proposal of M. Anglada, brôme derives from the Greek βρωμος
24.
Iodine
–
Iodine is a chemical element with symbol I and atomic number 53. The heaviest of the halogens, it exists as a lustrous. The elemental form was discovered by the French chemist Bernard Courtois in 1811 and it was named two years later by Joseph-Louis Gay-Lussac from this property, after the Greek ἰωδης violet-coloured. Iodine occurs in many states, including iodide, iodate. It is the least abundant of the halogens, being the sixty-first most abundant element. It is even less abundant than the rare earths. It is the heaviest essential element, iodine is found in the thyroid hormones. Iodine deficiency affects two billion people and is the leading preventable cause of intellectual disabilities. The dominant producers of today are Chile and Japan. Iodine and its compounds are used in nutrition. Due to its atomic number and ease of attachment to organic compounds. Because of the specificity of its uptake by the human body, iodine is also used as a catalyst in the industrial production of acetic acid and some polymers. In 1811, iodine was discovered by French chemist Bernard Courtois, at that time of the Napoleonic Wars, saltpeter was in great demand in France. Saltpeter produced from French nitre beds required sodium carbonate, which could be isolated from seaweed collected on the coasts of Normandy, to isolate the sodium carbonate, seaweed was burned and the ash washed with water. The remaining waste was destroyed by adding sulfuric acid, Courtois once added excessive sulfuric acid and a cloud of purple vapour rose. He noted that the vapour crystallised on cold surfaces, making dark crystals, Courtois suspected that this material was a new element but lacked funding to pursue it further. Courtois gave samples to his friends, Charles Bernard Desormes and Nicolas Clément and he also gave some of the substance to chemist Joseph Louis Gay-Lussac, and to physicist André-Marie Ampère. On 29 November 1813, Desormes and Clément made Courtois discovery public and they described the substance to a meeting of the Imperial Institute of France
25.
Organofluorine chemistry
–
Organofluorine chemistry describes the chemistry of the organofluorines, organic compounds that contain the carbon–fluorine bond. Organofluorine compounds find diverse applications ranging from oil and water repellents to pharmaceuticals, refrigerants, in addition to these applications, some organofluorine compounds are pollutants because of their contributions to ozone depletion, global warming, bioaccumulation, and toxicity. The area of organofluorine chemistry often requires special techniques associated with the handling of fluorinating agents, fluorine has several distinctive differences from all other substituents encountered in organic molecules. As a result, the physical and chemical properties of organofluorines can be distinctive in comparison to other organohalogens, the carbon–fluorine bond is one of the strongest in organic chemistry. This is significantly stronger than the bonds of carbon with other halogens and is one of the reasons why fluoroorganic compounds have high thermal and chemical stability, the carbon–fluorine bond is relatively short. The Van der Waals radius of the substituent is only 1.47 Å. This, together with the bond length, is the reason why there is no steric strain in polyfluorinated compounds. This is another reason for their thermal stability. In addition, the substituents in polyfluorinated compounds efficiently shield the carbon skeleton from possible attacking reagents. This is another reason for the chemical stability of polyfluorinated compounds. Fluorine has the highest electronegativity of all elements,3.98 and this causes the high dipole moment of C-F bond. Fluorine has the lowest polarizability of all atoms,0.56 × 10−24 cm3, in comparison to aryl chlorides and bromides, aryl fluorides form Grignard reagents only reluctantly. On the other hand, aryl fluorides, e. g. fluoroanilines and fluorophenols, formally, fluorocarbons only contain carbon and fluorine. They can be gases, liquids, waxes, or solids, the simplest fluorocarbon is the gas tetrafluoromethane. Because of the reduced intermolecular van der Waals interactions, fluorocarbon-based compounds are used as lubricants or are highly volatile. Fluorocarbon liquids have medical applications as oxygen carriers, the structure of organofluorine compounds can be distinctive. As shown below, perfluorinated aliphatic compounds tend to segregate from hydrocarbons and this like dissolves like effect is related to the usefulness of fluorous phases and the use of PFOA in processing of fluoropolymers. Polymeric organofluorine compounds are numerous and commercially significant and they range from fully fluorinated species, e. g. PTFE to partially fluorinated, e. g. polyvinylidene fluoride and polychlorotrifluoroethylene
26.
Organochloride
–
The chloroalkane class provides common examples. The wide structural variety and divergent chemical properties of lead to a broad range of names. Organochlorides are very useful compounds in many applications, but some are of profound environmental concern, chlorination modifies the physical properties of hydrocarbons in several ways. The compounds are typically denser than water due to the atomic weight of chlorine versus hydrogen. Aliphatic organochlorides are alkylating agents because chloride is a leaving group, many organochlorine compounds have been isolated from natural sources ranging from bacteria to humans. Chlorinated organic compounds are found in every class of biomolecules including alkaloids, terpenes, amino acids, flavonoids, steroids. In addition, a variety of simple chlorinated hydrocarbons including dichloromethane, chloroform, a majority of the chloromethane in the environment is produced naturally by biological decomposition, forest fires, and volcanoes. The natural organochloride epibatidine, an alkaloid isolated from tree frogs, has potent analgesic effects and has stimulated research into new pain medication, alkanes and aryl alkanes may be chlorinated under free radical conditions, with UV light. However, the extent of chlorination is difficult to control, aryl chlorides may be prepared by the Friedel-Crafts halogenation, using chlorine and a Lewis acid catalyst. The haloform reaction, using chlorine and sodium hydroxide, is able to generate alkyl halides from methyl ketones. Chlorine adds to the bonds on alkenes and alkynes as well. Alkenes react with chloride to give alkyl chlorides. Secondary and tertiary alcohols react with chloride to give the corresponding chlorides. Alternatively, the Appel reaction can be used, Alkyl chlorides are versatile building blocks in organic chemistry, while alkyl bromides and iodides are more reactive, alkyl chlorides tend to be less expensive and more readily available. Alkyl chlorides readily undergo attack by nucleophiles, heating alkyl halides with sodium hydroxide or water gives alcohols. Reaction with alkoxides or aroxides give ethers in the Williamson ether synthesis, Alkyl chlorides readily react with amines to give substituted amines. Alkyl chlorides are substituted by softer halides such as the iodide in the Finkelstein reaction, reaction with other pseudohalides such as azide, cyanide, and thiocyanate are possible as well. In the presence of a base, alkyl chlorides undergo dehydrohalogenation to give alkenes or alkynes
27.
Organobromine compound
–
Organobromine compounds, also called organobromides, are organic compounds that contain carbon bonded to bromine. The most pervasive is the naturally produced bromomethane, one prominent application is the use of polybrominated diphenyl ethers as fire-retardants. A variety of organobromine compounds are found in nature. Organobromine compounds have fallen under increased scrutiny for their environmental impact, most organobromine compounds, like most organohalide compounds, are relatively nonpolar. Bromine is more electronegative than carbon, consequently, the carbon in a carbon–bromine bond is electrophilic, i. e. alkyl bromides are alkylating agents. Carbon–halogen bond strengths, or bond dissociation energies are of 115,83.7,72.1, the reactivity of organobromine compounds resembles but is intermediate between the reactivity of organochlorine and organoiodine compounds. For many applications, organobromides represent a compromise of reactivity and cost, the principal reactions for organobromides include dehydrobromination, Grignard reactions, reductive coupling, and nucleophilic substitution. Alkenes reliably add bromine without catalysis to give the vicinal dibromides, catalysts such as AlBr3 or FeBr3 are needed for the reaction to happen on aromatic rings. Chlorine-based catalysts could be used, but yield would drop slightly as dihalogens could form, free-radical substitution with bromine is commonly used to prepare organobromine compounds. Carbonyl-containing, benzylic, allylic substrates are especially prone to this reactions, free-radical addition is used commercially for the synthesis of 1-bromoalkanes, precursors to tertiary amines and quaternary ammonium salts. 2-Phenethyl bromide is produced via this route from styrene, hydrogen bromide can also be used to convert alcohols to alkyl bromides. Bromide ions, as provided by salts like sodium bromide, function as a nucleophiles in the formation of organobromine compounds by displacement. An example of this salt mediated bromide displacement is the use of Copper bromide on ketones, the most prominent member is tetrabromobisphenol-A. It and tetrabromophthalic anhydride are precursors to polymers wherein the backbone features covalent carbon-bromine bonds, other fire retardants, such as hexabromocyclododecane and the bromodiphenyl ethers, are additives and are not chemically attached to the material they protect. The use of organobromine fire-retardants is growing but is controversial because they are persistent pollutants. Ethylene bromide, obtained by addition of bromine to ethylene, was once of commercial significance as a component of leaded gasoline and it was also a popular fumigant in agriculture, displacing 1, 2-dibromo-3-chloropropane. Both applications are declining owing to environmental and health considerations, methyl bromide is also an effective fumigant, but its production and use are controlled by the Montreal Protocol. Growing in use are organobromine biocides used in water treatment, representative agents include bromoform and dibromodimethylhydantoin
28.
Organoiodine compound
–
Organoiodine compounds are organic compounds that contain one or more carbon–iodine bonds. They occur widely in organic chemistry, but are rare in nature. The thyroxine hormones are organoiodine compounds that are required for health, almost all organoiodine compounds feature iodide connected to one carbon center. These are usually classified as derivatives of I−, some organoiodine compounds feature iodine in higher oxidation states. The C–I bond is the weakest of the carbon–halogen bonds and these bond strengths correlate with the electronegativity of the halogen, decreasing in the order F > Cl > Br > I. This periodic order also follows the atomic radius of halogens and the length of the carbon-halogen bond, of the halides, iodide usually is the best leaving group. Because of the weakness of the C-I bond, samples of organoiodine compounds are often due to an impurity of I2. A noteworthy aspect of organoiodine compounds is their density, which arises from the high atomic weight of iodine. For example, one millilitre of methylene iodide weighs 3.325 g, few organoiodine compounds are important industrially, at least in terms of large scale production. Iodide-containing intermediates are common in organic synthesis, because of the easy formation, industrially significant organoiodine compounds, often used as disinfectants or pesticides, are iodoform, methylene iodide, and methyl iodide. Ioxynil, which inhibits photosynthesis at photosystem II, is among the very few organoiodine herbicides, a member of the hydroxybenzonitrile herbicide class, ioxynil is an iodinated analog of the brominated herbicide, bromoxynil. Iodinated and brominated organic compounds are of concern as environmental contaminants owing to limited information available on environment fate behavior. However, recent reports have shown promise in biological detoxification of these classes of contaminants, for example, Iodotyrosine deiodinase is a mammalian enzyme with the unusual function of aerobic reductive dehalogenation of iodine- or bromine-substituted organic substrates. Bromoxynil and ioxynil herbicides have been shown to undergo a variety of environmental transformations, polyiodoorganic compounds are sometimes employed as X-ray contrast agents, in fluoroscopy, a type of medical imaging. This application exploits the X-ray absorbing ability of the heavy iodine nucleus, a variety of agents are available commercially, many are derivatives of 1,3, 5-triiodobenzene and contain about 50% by weight iodine. For most applications, the agent must be soluble in water and, of course, non-toxic. A representative reagent is Ioversol, which has water-solubilizing diol substituents, typical applications include urography and angiography. In terms of health, the most important organoiodine compounds are the two thyroid hormones thyroxine and triiodothyronine
29.
Intermolecular force
–
Intermolecular forces are weak relative to intramolecular forces – the forces which hold a molecule together. For example, the covalent bond, involving sharing electron pairs between atoms, is stronger than the forces present between neighboring molecules. Both sets of forces are essential parts of force fields used in molecular mechanics. The investigation of intermolecular forces starts from macroscopic observations which indicate the existence and these observations include non-ideal-gas thermodynamic behavior reflected by virial coefficients, vapor pressure, viscosity, superficial tension, and absorption data. The first reference to the nature of microscopic forces is found in Alexis Clairauts work Theorie de la Figure de la Terre, other scientists who have contributed to the investigation of microscopic forces include, Laplace, Gauss, Maxwell and Boltzmann. The link to microscopic aspects is given by virial coefficients and Lennard-Jones potentials, dipole-dipole interactions are electrostatic interactions between permanent dipoles in molecules. These interactions tend to align the molecules to increase attraction, an example of a dipole-dipole interaction can be seen in hydrogen chloride, the positive end of a polar molecule will attract the negative end of the other molecule and influence its position. Polar molecules have a net attraction between them, examples of polar molecules include hydrogen chloride and chloroform. H δ + − Cl δ − ⋯ H δ + − Cl δ − Often molecules contain dipolar groups and this occurs if there is symmetry within the molecule that causes the dipoles to cancel each other out. This occurs in such as tetrachloromethane and carbon dioxide. The dipole-dipole interaction between two atoms is usually zero, since atoms rarely carry a permanent dipole. Ion-dipole and ion-induced dipole forces are similar to dipole-dipole and induced-dipole interactions but involve ions, ion-dipole and ion-induced dipole forces are stronger than dipole-dipole interactions because the charge of any ion is much greater than the charge of a dipole moment. Ion-dipole bonding is stronger than hydrogen bonding, an ion-dipole force consists of an ion and a polar molecule interacting. They align so that the positive and negative groups are next to one another, an ion-induced dipole force consists of an ion and a non-polar molecule interacting. Like a dipole-induced dipole force, the charge of the ion causes distortion of the cloud on the non-polar molecule. A hydrogen bond is the attraction between the pair of an electronegative atom and a hydrogen atom that is bonded to either nitrogen, oxygen. The hydrogen bond is described as a strong electrostatic dipole-dipole interaction. Intermolecular hydrogen bonding is responsible for the boiling point of water compared to the other group 16 hydrides
30.
London dispersion force
–
London dispersion forces are a type of force acting between atoms and molecules. They are part of the van der Waals forces, the LDF is named after the German-American physicist Fritz London. The LDF is a weak intermolecular force arising from quantum-induced instantaneous polarization multipoles in molecules and they can therefore act between molecules without permanent multipole moments. London forces are exhibited by non-polar molecules because of the movements of the electrons in interacting molecules. Because the electrons in adjacent molecules flee as they repel each other and this is frequently described as the formation of instantaneous dipoles that attract each other. London forces become stronger as the atom in question becomes larger and this is due to the increased polarizability of molecules with larger, more dispersed electron clouds. This trend is exemplified by the halogens, fluorine and chlorine are gases at room temperature, bromine is a liquid, and iodine is a solid. The London forces also become stronger with larger amounts of surface contact, greater surface area means closer interaction between different molecules. The first explanation of the attraction between noble gas atoms was given by Fritz London in 1930 and he used a quantum-mechanical theory based on second-order perturbation theory. The perturbation is because of the Coulomb interaction between the electrons and nuclei of the two moieties, the second-order perturbation expression of the interaction energy contains a sum over states. The states appearing in this sum are simple products of the electronic states of the monomers. Thus, no intermolecular antisymmetrization of the states is included. London wrote Taylor series expansion of the perturbation in 1 R and this expansion is known as the multipole expansion because the terms in this series can be regarded as energies of two interacting multipoles, one on each monomer. Substitution of the form of V into the second-order energy yields an expression that resembles somewhat an expression describing the interaction between instantaneous multipoles. Additionally, an approximation, named after Albrecht Unsöld, must be introduced in order to obtain a description of London dispersion in terms of dipole polarizabilities and ionization potentials. In this manner, the approximation is obtained for the dispersion interaction E A B d i s p between two atoms A and B. Here α A and α B are the dipole polarizabilities of the respective atoms, the quantities I A and I B are the first ionization potentials of the atoms, and R is the intermolecular distance. E A B d i s p ≈ −32 I A I B I A + I B α A α B R6 Note that this final London equation does not contain instantaneous dipoles
31.
Carbon tetraiodide
–
Carbon tetraiodide is a tetrahalomethane with the molecular formula CI4. Being bright red, it is a rare example of a highly colored methane derivative. It is only 2% by weight carbon, although other methane derivatives are known with still less carbon, the tetrahedral molecule features C-I distances of 2.12 ±0.02 Å. The molecule is slightly crowded with short contacts between iodine atoms of 3.459 ±0.03 Å, and possibly for this reason, hexaiodoethane is unknown, probably for the same reason. Carbon tetraiodide crystallizes in tetragonal crystal structure and it has zero dipole moment due to its symmetrically substituted tetrahedral molecule. Carbon tetraiodide is slightly reactive towards water, giving iodoform and I2>, otherwise it is soluble in nonpolar organic solvents. It decomposes thermally and photochemically to tetraiodoethylene, C2I4 and its synthesis entails AlCl3-catalyzed halide exchange, which is conducted at room temperature, CCl4 +4 EtI → CI4 +4 EtCl The product crystallizes from the reaction solution. Carbon tetraiodide is used as a reagent, often upon reaction with bases. Ketones are converted to 1, 1-diiodoalkenes upon treatment with triphenylphosphine, alcohols are converted in and to iodide, by a mechanism similar to the Appel reaction. In an Appel reaction, carbon tetrachloride is used to generate alkyl chlorides from alcohols, manufacturers recommend that carbon tetraiodide be stored near 0 °C. As a ready source of iodine, it is an irritant, in general, perhalogenated organic compounds should be considered toxic, with the narrow exception of small perfluoroalkanes. Application to the Preparation of Carbon Tetraiodide and Related Halides” Journal of the American Chemical Society 1945,67,1643
32.
Tetrafluoromethane
–
Tetrafluoromethane, also known as carbon tetrafluoride, is the simplest fluorocarbon. It has a high bond strength due to the nature of the carbon–fluorine bond. It can also be classified as a haloalkane or halomethane, Tetrafluoromethane is a potent greenhouse gas. Carbon–fluorine bonds are the strongest single bonds in organic chemistry, additionally, they strengthen as more carbon–fluorine bonds are added to the same carbon. This effect is due to the increased coulombic attractions between the atoms and the carbon because the carbon has a positive partial charge of 0.76. Tetrafluoromethane is the product when any carbon compound, including itself, is burned in an atmosphere of fluorine. With hydrocarbons, hydrogen fluoride is a coproduct and it was first reported in 1926. It can also be prepared by the fluorination of carbon dioxide, although it can be made from myriad precursors and fluorine, elemental fluorine is expensive and difficult to handle. SiC +4 F2 → CF4 + SiF4 Tetrafluoromethane, like other fluorocarbons, is stable due to the strength of its carbon–fluorine bonds. The bonds in tetrafluoromethane have an energy of 515 kJ⋅mol−1. As a result, it is inert to acids and hydroxides, however, it reacts explosively with alkali metals. Thermal decomposition or combustion of CF4 produces toxic gases and in the presence of water will also yield hydrogen fluoride and it is very slightly soluble in water, but miscible with organic solvents. Tetrafluoromethane is sometimes used as a low temperature refrigerant and it is used in electronics microfabrication alone or in combination with oxygen as a plasma etchant for silicon, silicon dioxide, and silicon nitride. It also has uses in neutron detectors Tetrafluoromethane is a potent greenhouse gas that contributes to the greenhouse effect, although structurally similar to chlorofluorocarbons, tetrafluoromethane does not deplete the ozone layer. This is because the depletion is caused by the atoms in CFCs. Carbon–fluorine bonds are stronger and less likely to dissociate, according to Guinness World Records Tetrafluoromethane is the most persistent greenhouse gas. Main industrial emissions of tetrafluoromethane besides hexafluoroethane are produced during production of aluminium using Hall-Héroult process, CF4 also is produced as product of the breakdown of more complex compounds such as halocarbons. Due to its density, tetrafluoromethane can displace air, creating a hazard in inadequately ventilated areas
33.
Alkylation
–
Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as a carbocation, a free radical. An alkyl group is a piece of a molecule with the general formula CnH2n+1, for example, a methyl group is a fragment of a methane molecule. Alkylating agents utilize selective alkylation by adding the desired aliphatic carbon chain to the chosen starting molecule. This is one of known chemical syntheses. Alkyl groups can also be removed in a known as dealkylation. In oil refining contexts, alkylation refers to a particular alkylation of isobutane with olefins, for upgrading of petroleum, alkylation produces synthetic C7–C8 alkylate, which is a premium blending stock for gasoline. In medicine, alkylation of DNA is used in chemotherapy to damage the DNA of cancer cells, alkylation is accomplished with the class of drugs called alkylating antineoplastic agents. Alkylating agents are classified according to their nucleophilic or electrophilic character, nucleophilic alkylating agents deliver the equivalent of an alkyl anion. Examples include the use of compounds such as Grignard, organolithium, organocopper. These compounds typically can add to an electron-deficient carbon atom such as at a carbonyl group, nucleophilic alkylating agents can also displace halide substituents on a carbon atom. In the presence of catalysts, they also alkylate alkyl and aryl halides, electrophilic alkylating agents deliver the equivalent of an alkyl cation. Examples include the use of alkyl halides with a Lewis acid catalyst to alkylate aromatic substrates in Friedel-Crafts reactions, alkyl halides can also react directly with amines to form C-N bonds, the same holds true for other nucleophiles such as alcohols, carboxylic acids, thiols, etc. Trimethyloxonium tetrafluoroborate and triethyloxonium tetrafluoroborate are particularly strong due to their overt positive charge. Electrophilic, soluble alkylating agents are very toxic, due to their ability to alkylate DNA. They should be handled with proper PPE, alkylated DNA either does not coil or uncoil properly, or cannot be processed by information-decoding enzymes. This results in cytotoxicity with the effects of inhibition the growth of the cell, however, mutations are also triggered, including carcinogenic mutations, explaining the higher incidence of cancer after exposure. For example, dimethyl sulfate alkylates the sodium salt of phenol to give anisole, the dimethyl sulfate is dealkylated to sodium methylsulfate
34.
Mechanistic organic photochemistry
–
Mechanistic organic photochemistry is that aspect of organic photochemistry which seeks to explain the mechanisms of organic photochemical reactions. The absorption of light by organic molecules very often leads to reactions. In the earliest days sunlight was employed while in modern times ultraviolet lamps are employed. Organic photochemistry has proven to be a useful synthetic tool. Complex organic products can be obtained simply, over the last century and earlier an immense number of photochemical reactions have been uncovered. In modern times the field is well understood and is used in organic synthesis. One of the earliest photochemical studies dealt with the natural product santonin, in the 19th century it had been observed by Ciamician that in Italian sunlight santonin gave several photoproducts. The structure of santonin was first correctly described by Clemo and Hayworth in 1929, the initial photoproduct obtained from santonin is lumisantonin. 1, the photoreaction involves a rearrangement, using steroid numbering, we note that the C-3 carbonyl group has moved to C-2, the C-4 methyl has moved to C-1, and the C-10 carbon has been inverted. A comparatively bizarre example was uncovered by Egbert Havinga in 1956, the curious result was activation on photolysis by a meta nitro group in contrast to the usual activation by ortho and para groups. Over the decades, many interesting but puzzling organic photochemical reactions were discovered that did not proceed by ordinary organic ground state processes, rather, they arose from the excited states of electrons in the compounds. The real problem was that, at the time, organic chemists were not versed in quantum mechanics, real mechanistic treatments were not possible. Starting in 1961 it was found that one could understand organic photochemical reactions in the context of the relevant excited states, one example is the n-pi* excitation of mono-carbonyl compounds, the simplest being that of formaldehyde. The structure was first described by Mulliken, the three-dimensional representation is simplified in the second line using a two-dimensional representation, which facilitates arrow pushing. In this early research simple Hückel computations were used to get excited state electron densities, the stereochemistry in Scheme 1 is shown three-dimensionally. The Hückel computations revealed that the beta-carbons of the ring had a large bond-order. As seen in the scheme a beta-beta bond is formed, subsequent to this, radiationless decay leads to a zwitterion ground state. The final rearrangement leads to lumisantonin as can be discerned by comparing the three-dimensional drawing with the earlier two-dimensional representation and this is followed by intersystem crossing to form the singlet ground state which is seen to be a zwitterion
35.
Mefloquine
–
Mefloquine, sold under the brand names Lariam among others, is a medication used to prevent or treat malaria. When used for prevention it is once a week and should be begun one or two weeks before potential exposure and continued for four weeks after potential exposure. It can be used to treat mild or moderate malaria but should not be used to treat severe malaria and it is therefore not recommended in people with a history of mental health problems or epilepsy. Common side effects include vomiting, diarrhea, headaches, and a rash and it is not recommended in pregnancy unless other options are not available. It should not be used during breast feeding, mefloquine was developed by the United States Army in the 1970s and came into use in the mid 1980s. It is on the World Health Organizations List of Essential Medicines and it is available as a generic medication. The wholesale price in the world is about 0.6 to 1.3 USD per dose. In the United States it costs about 10 USD a dose, mefloquine is used to both prevent and treat certain forms of malaria. It is typically taken for one to two weeks before entering an area with malaria, doxycycline and atovaquone/proguanil provide protection within one to two days and may be better tolerated. If a person becomes ill with malaria despite prophylaxis with mefloquine, mefloquine is widely used for the treatment of malaria in pregnancy. Limited data suggests that it is safe for this purpose, resistance to mefloquine is now common around the west border in Cambodia and other parts of Southeast Asia. The mechanism of resistance is by increase in Pfmdr1 copy number, mefloquine is contraindicated in those with a previous history of seizures or a recent history of psychiatric disorders. Severe side effects requiring hospitalization are rare, compared to other malaria prophylaxis regimens, mefloqinone may produce more side effects in non-pregnant travelers. In pregnant travelers, it appears to pose minimal risk to the fetus, psychiatric effects include nightmares, visual and auditory hallucinations, anxiety, depression, unusual behavior, and suicidal ideations, among others. Neurologic effects include dizziness, loss of balance, and tinnitus, the label warns that mild symptoms may presage more serious ones, and that the drug should be discontinued at the first sign of symptoms. Mefloquine should not be used in people with a history of psychiatric problems, central nervous system events requiring hospitalization occur in about one in 10,000 people taking mefloquine for malaria prevention, with milder events in up to 25%. When some measure of severity is applied to the rating of adverse events. Mefloquine may cause abnormalities with heart rhythms that are visible on electrocardiograms, combining mefloquine with other drugs that cause similar effects, such as quinine or quinidine, can increase these effects
36.
Ether
–
Ethers are a class of organic compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula R–O–R′, where R and R′ represent the alkyl or aryl groups, a typical example of the first group is the solvent and anesthetic diethyl ether, commonly referred to simply as ether. Ethers are common in chemistry and pervasive in biochemistry, as they are common linkages in carbohydrates. Ethers feature C–O–C linkage defined by an angle of about 110°. The barrier to rotation about the C–O bonds is low, the bonding of oxygen in ethers, alcohols, and water is similar. In the language of valence bond theory, the hybridization at oxygen is sp3, oxygen is more electronegative than carbon, thus the hydrogens alpha to ethers are more acidic than in simple hydrocarbons. They are far less acidic than hydrogens alpha to carbonyl groups, depending on the groups at R and R′, ethers are classified into two types, Simple ethers or symmetrical ethers, e. g. diethyl ether, dimethyl ether, etc. Mixed ethers or unsymmetrical ethers, e. g. methyl ethyl ether, methyl phenyl ether, in the IUPAC nomenclature system, ethers are named using the general formula alkoxyalkane, for example CH3–CH2–O–CH3 is methoxyethane. If the ether is part of a complex molecule, it is described as an alkoxy substituent. The simpler alkyl radical is written in front, so CH3–O–CH2CH3 would be given as methoxyethane, IUPAC rules are often not followed for simple ethers. The trivial names for simple ethers are a composite of the two followed by ether. For example, ethyl ether, diphenylether. As for other compounds, very common ethers acquired names before rules for nomenclature were formalized. Diethyl ether is called ether, but was once called sweet oil of vitriol. Methyl phenyl ether is anisole, because it was found in aniseed. Acetals are another class of ethers with characteristic properties, polyethers are compounds with more than one ether group. The crown ethers are examples of small polyethers, some toxins produced by dinoflagellates such as brevetoxin and ciguatoxin are extremely large and are known as cyclic or ladder polyethers. Polyether generally refers to polymers which contain the functional group in their main chain
37.
Inhalational anaesthetic
–
An inhalational anaesthetic is a chemical compound possessing general anaesthetic properties that can be delivered via inhalation. They are administered by anaesthetists through a mask, laryngeal mask airway or tracheal tube connected to an anaesthetic vaporiser. All of these share the property of being quite hydrophobic. The ideal volatile anaesthetic agent offers smooth and reliable induction and maintenance of general anaesthesia with minimal effects on other organ systems. In addition it is odourless or pleasant to inhale, safe for all ages and in pregnancy, not metabolised, rapid in onset and offset, potent, none of the agents currently in use are ideal, although many have some of the desirable characteristics. For example, sevoflurane is pleasant to inhale and is rapid in onset and offset and it is also safe for all ages. However, it is expensive, and approximately half as potent as isoflurane, other gases or vapors which produce general anaesthesia by inhalation include nitrous oxide, cyclopropane and xenon. These are stored in gas cylinders and administered using flowmeters, rather than vaporisers, cyclopropane is explosive and is no longer used for safety reasons, although otherwise it was found to be an excellent anaesthetic. Xenon is odourless and rapid in onset, but is expensive and requires specialized equipment to administer, under hyperbaric conditions, other gases such as nitrogen, and noble gases such as argon, krypton, and xenon become anaesthetics. When inhaled at high pressures, nitrogen begins to act as an anaesthetic agent. However, the minimum alveolar concentration for nitrogen is not achieved until pressures of about 20 to 30 atm are attained, argon is slightly more than twice as anaesthetic as nitrogen per unit of partial pressure. Xenon however is an anaesthetic at 80% concentration and normal atmospheric pressure. The full mechanism of action of volatile anaesthetic agents is unknown and has been the subject of intense debate. Anesthetics have been used for 160 years, and how work is one of the great mysteries of neuroscience, says anaesthesiologist James Sonner of the University of California. Anaesthesia research has been for a time a science of untestable hypotheses, notes Neil L. Harrison of Cornell University. Most of the injectable anesthetics appear to act on a molecular target. It looks like inhaled anesthetics act on multiple molecular targets and that makes it a more difficult problem to pick apart. However, the agent may bind to a receptor with a weak interaction, a physical interaction such as swelling of nerve cell membranes from gas solution in the lipid bilayer may be operative
38.
Methoxyflurane
–
It was first synthesized in the late 1940s by William T. Miller and his team of chemists following their involvement in the Manhattan Project. Methoxyflurane is a potent and highly lipid-soluble anesthetic agent, characterized by very slow induction. It is non-flammable, has relatively mild effects, and it does not predispose the heart to rhythm disturbances. It is, however, a significant respiratory depressant, Methoxyflurane has powerful analgesic properties at well below full anesthetic doses. It was utilized in devices for obstetric analgesia, in a manner that foreshadowed the patient-controlled analgesia infusion pumps of today. The biodegradation of methoxyflurane produces inorganic fluoride and dichloroacetic acid, the combined effects of these two compounds may be responsible for the toxicity of methoxyflurane to some of the major organs of the human body. Methoxyflurane was determined to be nephrotoxic in a dose-dependent response and hepatotoxic at anesthetic doses in 1973, the drug is currently only available from one manufacturer. It is self-administered to children and adults using the Penthrox inhaler, a non-opioid alternative to morphine, it is also easier to use than nitrous oxide. The device is referred to as the green whistle, due to its appearance. Each 3 milliliter dose lasts approximately 30 minutes, pain relief begins after 6–8 breaths and continues for several minutes after stopping inhalation. The maximum recommended dose is 6 milliliters per day or 15 milliliters per week because of the risk of cumulative dose-related nephrotoxicity and it is a halogenated ether in form of a clear, colorless liquid, and its vapor has a strong fruity aroma. It is miscible with ethanol, acetone, chloroform, diethyl ether, with a minimum alveolar concentration of 0. 16%, methoxyflurane is an extremely potent anesthetic agent. It is a powerful agent at well below full anesthetic concentrations. Because of its low volatility and very high boiling point, methoxyflurane has a low pressure at ambient temperature. It is therefore difficult to vaporize methoxyflurane using conventional anesthetic vaporizers. The carbon–fluorine bond, a component of all compounds, is the strongest chemical bond in organic chemistry. Furthermore, this bond becomes shorter and stronger as more atoms are added to the same carbon on a given molecule. Because of this, fluoroalkanes are some of the most chemically stable organic compounds, Methoxyflurane has a very high lipid solubility, which gives it very slow pharmacokinetics, this being undesirable for routine application in the clinical setting
. PMID 19363038.
Media related to Haloalkanes at Wikimedia Commons