Nitrate is a polyatomic ion with the molecular formula NO−3 and a molecular mass of 62.0049 u. Organic compounds that contain the nitrate ester as a functional group are called nitrates; the anion is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a formal charge of −1; this results from a combination formal charge in which each of the three oxygens carries a −2⁄3 charge, whereas the nitrogen carries a +1 charge, all these adding up to formal charge of the polyatomic nitrate ion. This arrangement is used as an example of resonance. Like the isoelectronic carbonate ion, the nitrate ion can be represented by resonance structures: Almost all inorganic nitrate salts are soluble in water at standard temperature and pressure. A common example of an inorganic nitrate salt is potassium nitrate. A rich source of inorganic nitrate in the human body comes from diets rich in leafy green foods, such as spinach and arugula.
NO − 3 is the viable active component within other vegetables. Dietary nitrate may be found in cured meats, various leafy vegetables, drinking water. Nitrate and water are converted in the body to nitric oxide. Anti-hypertensive diets, such as the DASH diet contain high levels of nitrates, which are first reduced to nitrite in the saliva, as detected in saliva testing, prior to forming nitric oxide. Nitrate salts are found on earth as large deposits of nitratine, a major source of sodium nitrate. Nitrates are produced by a number of species of nitrifying bacteria, the nitrate compounds for gunpowder were produced, in the absence of mineral nitrate sources, by means of various fermentation processes using urine and dung. Nitrates are found in fertilizers; as a byproduct of lightning strikes in earth's nitrogen-oxygen rich atmosphere, nitric acid is produced when nitrogen dioxide reacts with water vapor. Nitrates are produced for use as fertilizers in agriculture because of their high solubility and biodegradability.
The main nitrate fertilizers are ammonium, sodium and calcium salts. Several million kilograms are produced annually for this purpose; the second major application of nitrates is as oxidizing agents, most notably in explosives where the rapid oxidation of carbon compounds liberates large volumes of gases. Sodium nitrate is used to remove air bubbles from some ceramics. Mixtures of the molten salt are used to harden some metals. Explosives and table tennis balls are made from celluloid. In the early 20th century, most motion picture film was made of nitrocellulose, but the intense flammability of the film led to it being replaced with "safety film" by the mid-20th-century. Although nitrites are the nitrogen compound chiefly used in meat curing, nitrates are used in certain specialty curing processes where a long release of nitrite from parent nitrate stores is needed; the use of nitrates in food preservation is controversial. This is due to the potential for the formation of nitrosamines when nitrates are present in high concentrations and the product is cooked at high temperatures.
The effect is seen for red or processed meat, but not for white fish. The production of carcinogenic nitrosamines may be inhibited by the use of the antioxidants vitamin C and the alpha-tocopherol form of vitamin E during curing. Under simulated gastric conditions, nitrosothiols rather than nitrosamines are the main nitroso species being formed; the use of either compound is therefore regulated. They are considered irreplaceable in the prevention of botulinum poisoning from consumption of cured dry sausages by preventing spore germination. Research has shown that dietary nitrate supplementation delivers positive results when testing endurance exercise performance; the historical standard method of testing for nitrate is the Cadmium Reduction Method, reliable and accurate although it is dependent on a toxic metal cadmium and thus not suitable for all applications. An alternative method for nitrate and nitrite analysis is enzymatic reduction using nitrate reductase, proposed by the US Environmental Protection Agency as an alternate test procedure for determining nitrate.
An open source photometer has been developed for this method to detect nitrate in water, forage, etc. Free nitrate ions in solution can be detected by a nitrate ion selective electrode; such electrodes function analogously to the pH selective electrode. This response is described by the Nernst equation. Nitrate poisoning can occur through enterohepatic metabolism of nitrate due to nitrite being an intermediate. Nitrites oxidize the iron atoms in hemoglobin from ferrous iron to ferric iron, rendering it unable to carry oxygen; this process can lead to generalized lack of oxygen in organ tissue and a dangerous condition called methemoglobinemia. Although nitrite converts to ammonia, if there is more nitrite than can be converted, the animal suffers from a lack of oxygen. Humans are subject to nitrate toxicity, with infants being vulnerable to methemoglobinemia. Methemoglobinemia in infants is known as blue baby syndrome. Methemoglobin occurs in normal people in concentrations of 0.5-3.0%. When concentrations of methemoglobin exceed 10%, clinical symptoms of methemoglobinemia occur.
Any concentration above
Raman spectroscopy. Raman spectroscopy is used in chemistry to provide a structural fingerprint by which molecules can be identified, it relies on inelastic scattering, or Raman scattering, of monochromatic light from a laser in the visible, near infrared, or near ultraviolet range. The laser light interacts with molecular vibrations, phonons or other excitations in the system, resulting in the energy of the laser photons being shifted up or down; the shift in energy gives information about the vibrational modes in the system. Infrared spectroscopy yields complementary, information. A sample is illuminated with a laser beam. Electromagnetic radiation from the illuminated spot is collected with a lens and sent through a monochromator. Elastic scattered radiation at the wavelength corresponding to the laser line is filtered out by either a notch filter, edge pass filter, or a band pass filter, while the rest of the collected light is dispersed onto a detector. Spontaneous Raman scattering is very weak, as a result the main difficulty of Raman spectroscopy is separating the weak inelastically scattered light from the intense Rayleigh scattered laser light.
Raman spectrometers used holographic gratings and multiple dispersion stages to achieve a high degree of laser rejection. In the past, photomultipliers were the detectors of choice for dispersive Raman setups, which resulted in long acquisition times. However, modern instrumentation universally employs notch or edge filters for laser rejection and spectrographs either axial transmissive, Czerny–Turner monochromator, or FT, CCD detectors; the advanced types of Raman spectroscopy include surface-enhanced Raman, resonance Raman, tip-enhanced Raman, polarized Raman, stimulated Raman, transmission Raman, spatially offset Raman, hyper Raman. The magnitude of the Raman effect correlates with polarizability of the electrons in a molecule, it is a form of inelastic light scattering. This excitation puts the molecule into a virtual energy state for a short time before the photon is emitted. Inelastic scattering means that the energy of the emitted photon is of either lower or higher energy than the incident photon.
After the scattering event, the sample is in a different vibrational state. For the total energy of the system to remain constant after the molecule moves to a new rovibronic state, the scattered photon shifts to a different energy, therefore a different frequency; this energy difference is equal to that between the initial and final rovibronic states of the molecule. If the final state is higher in energy than the initial state, the scattered photon will be shifted to a lower frequency so that the total energy remains the same; this shift in frequency is called downshift. If the final state is lower in energy, the scattered photon will be shifted to a higher frequency, called an anti-Stokes shift, or upshift. For a molecule to exhibit a Raman effect, there must be a change in its electric dipole-electric dipole polarizability with respect to the vibrational coordinate corresponding to the rovibronic state; the intensity of the Raman scattering is proportional to this polarizability change. Therefore, the Raman spectrum depends on the rovibronic states of the molecule.
The Raman effect is based on the interaction between the electron cloud of a sample and the external electric field of the monochromatic light, which can create an induced dipole moment within the molecule based on its polarizability. Because the laser light does not excite the molecule there can be no real transition between energy levels; the Raman effect should not be confused with emission, where a molecule in an excited electronic state emits a photon and returns to the ground electronic state, in many cases to a vibrationally excited state on the ground electronic state potential energy surface. Raman scattering contrasts with infrared absorption, where the energy of the absorbed photon matches the difference in energy between the initial and final rovibronic states; the dependence of Raman on the electric dipole-electric dipole polarizability derivative differs from IR spectroscopy, which depends on the electric dipole moment derivative, the atomic polar tensor. This contrasting feature allows rovibronic transitions that might not be active in IR to be analyzed using Raman spectroscopy, as exemplified by the rule of mutual exclusion in centrosymmetric molecules.
Transitions which have large Raman intensities have weak IR intensities and vice versa. If a bond is polarized, a small change in its length such as that occurs during a vibration, has only a small resultant effect on polarization. Vibrations involving polar bonds are therefore, comparatively weak Raman scatterers; such polarized bonds, carry their electrical charges during the vibrational motion, this results in a larger net dipole moment change during the vibration, producing a strong IR absorption band. Conversely neutral bonds suffer large changes in polarizability during a vibration. However, the dipole moment is not affected such that while vibrations involving predominantly this type of bond are strong Raman scatterers, they are weak in the IR. A third vibrational spectroscopy technique, inelastic incoherent n
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table, a reactive nonmetal, an oxidizing agent that forms oxides with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. As compounds including oxides, the element makes up half of the Earth's crust. Dioxygen is used in cellular respiration and many major classes of organic molecules in living organisms contain oxygen, such as proteins, nucleic acids and fats, as do the major constituent inorganic compounds of animal shells and bone. Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms. Oxygen is continuously replenished in Earth's atmosphere by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide.
Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone absorbs ultraviolet UVB radiation and the high-altitude ozone layer helps protect the biosphere from ultraviolet radiation. However, ozone present at the surface is a byproduct of thus a pollutant. Oxygen was isolated by Michael Sendivogius before 1604, but it is believed that the element was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, Joseph Priestley in Wiltshire, in 1774. Priority is given for Priestley because his work was published first. Priestley, called oxygen "dephlogisticated air", did not recognize it as a chemical element; the name oxygen was coined in 1777 by Antoine Lavoisier, who first recognized oxygen as a chemical element and characterized the role it plays in combustion. Common uses of oxygen include production of steel and textiles, brazing and cutting of steels and other metals, rocket propellant, oxygen therapy, life support systems in aircraft, submarines and diving.
One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neck. Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries Leonardo da Vinci built on Philo's work by observing that a portion of air is consumed during combustion and respiration. In the late 17th century, Robert Boyle proved. English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. In one experiment, he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjects.
From this he surmised that nitroaereus is consumed in both combustion. Mayow observed that antimony increased in weight when heated, inferred that the nitroaereus must have combined with it, he thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract "De respiratione". Robert Hooke, Ole Borch, Mikhail Lomonosov, Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element; this may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, modified by the chemist Georg Ernst Stahl by 1731, phlogiston theory stated that all combustible materials were made of two parts.
One part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. Combustible materials that leave little residue, such as wood or coal, were thought to be made of phlogiston. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test the idea. Polish alchemist and physician Michael Sendivogius in his work De Lapide Philosophorum Tractatus duodecim e naturae fonte et manuali experientia depromti described a substance contained in air, referring to it as'cibus vitae', this substance is identical with oxygen. Sendivogius, during his experiments performed between 1598 and 1604, properly recognized that the substance is equivalent to the gaseous byproduct released by the thermal decomposition of potassium nitrate. In Bugaj’s view, the isolation of oxygen and the proper association of the substance to that part of air, required for life, lends sufficient weight to the discovery of oxygen by Sendivogius.
Simplified molecular-input line-entry system
The simplified molecular-input line-entry system is a specification in the form of a line notation for describing the structure of chemical species using short ASCII strings. SMILES strings can be imported by most molecule editors for conversion back into two-dimensional drawings or three-dimensional models of the molecules; the original SMILES specification was initiated in the 1980s. It has since been extended. In 2007, an open standard called. Other linear notations include the Wiswesser line notation, ROSDAL, SYBYL Line Notation; the original SMILES specification was initiated by David Weininger at the USEPA Mid-Continent Ecology Division Laboratory in Duluth in the 1980s. Acknowledged for their parts in the early development were "Gilman Veith and Rose Russo and Albert Leo and Corwin Hansch for supporting the work, Arthur Weininger and Jeremy Scofield for assistance in programming the system." The Environmental Protection Agency funded the initial project to develop SMILES. It has since been modified and extended by others, most notably by Daylight Chemical Information Systems.
In 2007, an open standard called "OpenSMILES" was developed by the Blue Obelisk open-source chemistry community. Other'linear' notations include the Wiswesser Line Notation, ROSDAL and SLN. In July 2006, the IUPAC introduced the InChI as a standard for formula representation. SMILES is considered to have the advantage of being more human-readable than InChI; the term SMILES refers to a line notation for encoding molecular structures and specific instances should be called SMILES strings. However, the term SMILES is commonly used to refer to both a single SMILES string and a number of SMILES strings; the terms "canonical" and "isomeric" can lead to some confusion when applied to SMILES. The terms are not mutually exclusive. A number of valid SMILES strings can be written for a molecule. For example, CCO, OCC and CC all specify the structure of ethanol. Algorithms have been developed to generate the same SMILES string for a given molecule; this SMILES is unique for each structure, although dependent on the canonicalization algorithm used to generate it, is termed the canonical SMILES.
These algorithms first convert the SMILES to an internal representation of the molecular structure. Various algorithms for generating canonical SMILES have been developed and include those by Daylight Chemical Information Systems, OpenEye Scientific Software, MEDIT, Chemical Computing Group, MolSoft LLC, the Chemistry Development Kit. A common application of canonical SMILES is indexing and ensuring uniqueness of molecules in a database; the original paper that described the CANGEN algorithm claimed to generate unique SMILES strings for graphs representing molecules, but the algorithm fails for a number of simple cases and cannot be considered a correct method for representing a graph canonically. There is no systematic comparison across commercial software to test if such flaws exist in those packages. SMILES notation allows the specification of configuration at tetrahedral centers, double bond geometry; these are structural features that cannot be specified by connectivity alone and SMILES which encode this information are termed isomeric SMILES.
A notable feature of these rules is. The term isomeric SMILES is applied to SMILES in which isotopes are specified. In terms of a graph-based computational procedure, SMILES is a string obtained by printing the symbol nodes encountered in a depth-first tree traversal of a chemical graph; the chemical graph is first trimmed to remove hydrogen atoms and cycles are broken to turn it into a spanning tree. Where cycles have been broken, numeric suffix labels are included to indicate the connected nodes. Parentheses are used to indicate points of branching on the tree; the resultant SMILES form depends on the choices: of the bonds chosen to break cycles, of the starting atom used for the depth-first traversal, of the order in which branches are listed when encountered. Atoms are represented by the standard abbreviation of the chemical elements, in square brackets, such as for gold. Brackets may be omitted in the common case of atoms which: are in the "organic subset" of B, C, N, O, P, S, F, Cl, Br, or I, have no formal charge, have the number of hydrogens attached implied by the SMILES valence model, are the normal isotopes, are not chiral centers.
All other elements must be enclosed in brackets, have charges and hydrogens shown explicitly. For instance, the SMILES for water may be written as either O or. Hydrogen may be written as a separate atom; when brackets are used, the symbol H is added if the atom in brackets is bonded to one or more hydrogen, followed by the number of hydrogen atoms if greater than 1 by the sign + for a positive charge or by - for a negative charge. For example, for ammonium. If there is more than one charge, it is written as digit.
Hygroscopy is the phenomenon of attracting and holding water molecules from the surrounding environment, at normal or room temperature. This is achieved through either absorption or adsorption with the adsorbing substance becoming physically changed somewhat; this could be an increase in volume, boiling point, viscosity, or other physical characteristic or property of the substance, as water molecules can become suspended between the substance's molecules in the process. The word hygroscopy uses combining forms of hygro- and -scopy. Unlike any other -scopy word, it no longer refers to a viewing or imaging mode, it did begin that way, with the word hygroscope referring in the 1790s to measuring devices for humidity level. These hygroscopes used materials, such as certain animal hairs, that appreciably changed shape and size when they became damp; such materials were said to be hygroscopic because they were suitable for making a hygroscope. Though, the word hygroscope ceased to be used for any such instrument in modern usage.
But the word hygroscopic lived on, thus hygroscopy. Nowadays an instrument for measuring humidity is called a hygrometer. Hygroscopic substances include cellulose fibers, caramel, glycerol, wood, sulfuric acid, many fertilizer chemicals, many salts, a wide variety of other substances. If a compound absorbs enough moisture so that it dissolves it is classed as hydrophilic. Zinc chloride and calcium chloride, as well as potassium hydroxide and sodium hydroxide, are so hygroscopic that they dissolve in the water they absorb: this property is called deliquescence. Not only is sulfuric acid hygroscopic in concentrated form but its solutions are hygroscopic down to concentrations of 10% v/v or below. A hygroscopic material will tend to become cakey when exposed to moist air; because of their affinity for atmospheric moisture, hygroscopic materials might require storage in sealed containers. When added to foods or other materials for the express purpose of maintaining moisture content, such substances are known as humectants.
Materials and compounds exhibit different hygroscopic properties, this difference can lead to detrimental effects, such as stress concentration in composite materials. The volume of a particular material or compound is affected by ambient moisture and may be considered its coefficient of hygroscopic expansion or coefficient of hygroscopic contraction —the difference between the two terms being a difference in sign convention. Differences in hygroscopy can be observed in plastic-laminated paperback book covers—often, in a moist environment, the book cover will curl away from the rest of the book; the unlaminated side of the cover absorbs more moisture than the laminated side and increases in area, causing a stress that curls the cover toward the laminated side. This is similar to the function of a thermostat's bi-metallic strip. Inexpensive dial-type hygrometers make use of this principle using a coiled strip. Deliquescence is the process by which a substance absorbs moisture from the atmosphere until it dissolves in the absorbed water and forms a solution.
Deliquescence occurs when the vapour pressure of the solution, formed is less than the partial pressure of water vapour in the air. While some similar forces are at work here, it is different from capillary attraction, a process where glass or other solid substances attract water, but are not changed in the process; the amount of moisture held by hygroscopic materials is proportional to the relative humidity. Tables containing this information can be found in many engineering handbooks and is available from suppliers of various materials and chemicals. Hygroscopy plays an important role in the engineering of plastic materials; some plastics are hygroscopic. The seeds of some grasses have hygroscopic extensions that bend with changes in humidity, enabling them to disperse over the ground. An example is Needle-and-Thread, Hesperostipa comata; each seed has an awn. Increased moisture causes it to untwist, upon drying, to twist again, thereby drilling the seed into the ground. Thorny dragons collect moisture in the dry desert via nighttime condensation of dew that forms on their skin and is channeled to their mouths in hygroscopic grooves between the spines of their skin.
Water collects in these grooves when it rains. Capillary action allows the lizard to suck in water from all over its body. Deliquescence, like hygroscopy, is characterized by a strong affinity for water and tendency to absorb moisture from the atmosphere if exposed to it. Unlike hygroscopy, deliquescence involves absorbing sufficient water to form an aqueous solution. Most deliquescent materials are salts, including calcium chloride, magnesium chloride, zinc chloride, ferric chloride, potassium carbonate, potassium phosphate, ferric ammonium citrate, ammonium nitrate, potassium hydroxide, sodium hydroxide. Owing to their high affinity for water, these substances are used as desiccants an application for concentrated sulfuric and phosphoric acids; these compounds are used in the chemical industry to remove the water produced by chemical reactions. Many engineering polymers are hygroscopic, including nylon, ABS, polycarbonate and poly. Other polyme
Nucleophile is a chemical species that donates an electron pair to form a chemical bond in relation to a reaction. All molecules or ions with a free pair of electrons or at least one pi bond can act as nucleophiles; because nucleophiles donate electrons, they are by definition Lewis bases. Nucleophilic describes the affinity of a nucleophile to the nuclei. Nucleophilicity, sometimes referred to as nucleophile strength, refers to a substance's nucleophilic character and is used to compare the affinity of atoms. Neutral nucleophilic reactions with solvents such as alcohols and water are named solvolysis. Nucleophiles may take part in nucleophilic substitution, whereby a nucleophile becomes attracted to a full or partial positive charge; the terms nucleophile and electrophile were introduced by Christopher Kelk Ingold in 1933, replacing the terms anionoid and cationoid proposed earlier by A. J. Lapworth in 1925; the word nucleophile is derived from philos for love. In general, in a row across the periodic table, the more basic the ion the more reactive it is as a nucleophile.
Within a series of nucleophiles with the same attacking element, the order of nucleophilicity will follow basicity. Sulfur is in general a better nucleophile than oxygen. Many schemes attempting to quantify relative nucleophilic strength have been devised; the following empirical data have been obtained by measuring reaction rates for a large number of reactions involving a large number of nucleophiles and electrophiles. Nucleophiles displaying the so-called alpha effect are omitted in this type of treatment; the first such attempt is found in the Swain–Scott equation derived in 1953: log 10 = s n This free-energy relationship relates the pseudo first order reaction rate constant, k, of a reaction, normalized to the reaction rate, k0, of a standard reaction with water as the nucleophile, to a nucleophilic constant n for a given nucleophile and a substrate constant s that depends on the sensitivity of a substrate to nucleophilic attack. This treatment results in the following values for typical nucleophilic anions: acetate 2.7, chloride 3.0, azide 4.0, hydroxide 4.2, aniline 4.5, iodide 5.0, thiosulfate 6.4.
Typical substrate constants are 0.66 for ethyl tosylate, 0.77 for β-propiolactone, 1.00 for 2,3-epoxypropanol, 0.87 for benzyl chloride, 1.43 for benzoyl chloride. The equation predicts that, in a nucleophilic displacement on benzyl chloride, the azide anion reacts 3000 times faster than water; the Ritchie equation, derived in 1972, is another free-energy relationship: log 10 = N + where N+ is the nucleophile dependent parameter and k0 the reaction rate constant for water. In this equation, a substrate-dependent parameter like s in the Swain–Scott equation is absent; the equation states that two nucleophiles react with the same relative reactivity regardless of the nature of the electrophile, in violation of the reactivity–selectivity principle. For this reason, this equation is called the constant selectivity relationship. In the original publication the data were obtained by reactions of selected nucleophiles with selected electrophilic carbocations such as tropylium or diazonium cations: or ions based on Malachite green.
Many other reaction types have since been described. Typical Ritchie N+ values are: 0.5 for methanol, 5.9 for the cyanide anion, 7.5 for the methoxide anion, 8.5 for the azide anion, 10.7 for the thiophenol anion. The values for the relative cation reactivities are −0.4 for the malachite green cation, +2.6 for the benzenediazonium cation, +4.5 for the tropylium cation. In the Mayr-Patz equation: log = s The second order reaction rate constant k at 20 °C for a reaction is related to a nucleophilicity parameter N, an electrophilicity parameter E, a nucleophile-dependent slope parameter s; the constant s is defined as 1 with 2-methyl-1-pentene as the nucleophile. Many of the constants have been derived from reaction of so-called benzhydrylium ions as the electrophiles: and a diverse collection of π-nucleophiles:. Typical E values are +6.2 for R = chlorine, +5.90 for R = hydrogen, 0 for R = methoxy and -7.02 for R = dimethylamine. Typical N values with s in parenthesis are -4.47 for electrophilic aromatic substitution to toluene, -0.41 for electrophilic addition to 1-phenyl-2-propene, 0.96 for addition to 2-methyl-1-pentene, -0.13 for reaction with triphenylallylsilane, 3.61 for reaction with 2-methylfuran, +7.48 for reaction with isobutenyltributylstannane and +13.36 for reaction with the enamine 7.
The range of organic reactions include SN2 reactions: With E = -9.15 for the S-methyldibenzothiophenium ion, typical nucleophile values N are 15.63 for piperidine, 10.49 for methoxide, 5.20 for water. In short, nucleophilicities towards sp2 or sp3 centers follow the same pattern. In an effort to unify the above described equations the Mayr equation is rewritten as: log = s E s N ( N + E
In situ is a Latin phrase that translates to "on site" or "in position." It can mean "locally", "on site", "on the premises", or "in place" to describe where an event takes place and is used in many different contexts. For example, in fields such as physics, chemistry, or biology, in situ may describe the way a measurement is taken, that is, in the same place the phenomenon is occurring without isolating it from other systems or altering the original conditions of the test. In the aerospace industry, equipment on-board aircraft must be tested in situ, or in place, to confirm everything functions properly as a system. Individually, each piece may work but interference from nearby equipment may create unanticipated problems. Special test equipment is available for this in situ testing. In archaeology, in situ refers to an artifact that has not been moved from its original place of deposition. In other words, it is stationary, meaning "still." An artifact being in situ is critical to the interpretation of that artifact and of the culture which formed it.
Once an artifact's'find-site' has been recorded, the artifact can be moved for conservation, further interpretation and display. An artifact, not discovered in situ is considered out of context and as not providing an accurate picture of the associated culture. However, the out of context artifact can provide scientists with an example of types and locations of in situ artifacts yet to be discovered; when excavating a burial site or surface deposit "in situ" refers to cataloging, mapping, photographing human remains in the position they are discovered. The label in situ indicates. Thus, an archaeological in situ find may be an object, looted from another place, an item of "booty" of a past war, a traded item, or otherwise of foreign origin; the in situ find site may still not reveal its provenance, but with further detective work may help uncover links that otherwise would remain unknown. It is possible for archaeological layers to be reworked on purpose or by accident. For example, in a Tell mound, where layers are not uniform or horizontal, or in land cleared or tilled for farming.
The term in situ is used to describe ancient sculpture, carved in place such as the Sphinx or Petra. This distinguishes it from statues that were carved and moved like the Colossi of Memnon, moved in ancient times. In art, in situ refers to a work of art made for a host site, or that a work of art takes into account the site in which it is installed or exhibited. For a more detailed account see: Site-specific art; the term can refer to a work of art created at the site where it is to be displayed, rather than one created in the artist's studio and installed elsewhere. In architectural sculpture the term is employed to describe sculpture, carved on a building from scaffolds, after the building has been erected. Used to describe the site specific dance festival “Insitu”. Held in Queens, New York. A fraction of the globular star clusters in our galaxy, as well as those in other massive galaxies, might have formed in situ; the rest might have been accreted from now defunct dwarf galaxies. In astronomy, in situ refers to in situ planet formation, in which planets are hypothesized to have been formed in the orbit that they are observed to be in rather than migrating from a different orbit.
In biology and biomedical engineering, in situ means to examine the phenomenon in place where it occurs. In the case of observations or photographs of living animals, it means that the organism was observed in the wild as it was found and where it was found; this means. The organism had not been moved to another location such as an aquarium; this phrase in situ when used in laboratory science such as cell science can mean something intermediate between in vivo and in vitro. For example, examining a cell within a whole organ intact and under perfusion may be in situ investigation; this would not be in vivo as the donor is sacrificed by experimentation, but it would not be the same as working with the cell alone. In vitro was among the first attempts to qualitatively and quantitatively analyze natural occurrences in the lab; the limitation of in vitro experimentation was that they were not conducted in natural environments. To compensate for this problem, in vivo experimentation allowed testing to occur in the original organism or environment.
To bridge the dichotomy of benefits associated with both methodologies, in situ experimentation allowed the controlled aspects of in vitro to become coalesced with the natural environmental compositions of in vivo experimentation. In conservation of genetic resources, "in situ conservation" is the process of protecting an endangered plant or animal species in its natural habitat, as opposed to ex situ conservation. In chemistry, in situ means "in the reaction mixture." There are numerous situations in which chemical intermediates are synthesized in situ in various processes. This may be done because the species is unstable, cannot be isolated, or out of convenience. Examples of the former include the Corey-Chaykovsky adrenochrome. In biomedical engineering, protein nanogels made by the in situ polymerization method provide a versatile platform for storage and release of therapeutic