1.
Chemistry
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Chemistry is a branch of physical science that studies the composition, structure, properties and change of matter. Chemistry is sometimes called the science because it bridges other natural sciences, including physics. For the differences between chemistry and physics see comparison of chemistry and physics, the history of chemistry can be traced to alchemy, which had been practiced for several millennia in various parts of the world. The word chemistry comes from alchemy, which referred to a set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism. An alchemist was called a chemist in popular speech, and later the suffix -ry was added to this to describe the art of the chemist as chemistry, the modern word alchemy in turn is derived from the Arabic word al-kīmīā. In origin, the term is borrowed from the Greek χημία or χημεία and this may have Egyptian origins since al-kīmīā is derived from the Greek χημία, which is in turn derived from the word Chemi or Kimi, which is the ancient name of Egypt in Egyptian. Alternately, al-kīmīā may derive from χημεία, meaning cast together, in retrospect, the definition of chemistry has changed over time, as new discoveries and theories add to the functionality of the science. The term chymistry, in the view of noted scientist Robert Boyle in 1661, in 1837, Jean-Baptiste Dumas considered the word chemistry to refer to the science concerned with the laws and effects of molecular forces. More recently, in 1998, Professor Raymond Chang broadened the definition of chemistry to mean the study of matter, early civilizations, such as the Egyptians Babylonians, Indians amassed practical knowledge concerning the arts of metallurgy, pottery and dyes, but didnt develop a systematic theory. Greek atomism dates back to 440 BC, arising in works by such as Democritus and Epicurus. In 50 BC, the Roman philosopher Lucretius expanded upon the theory in his book De rerum natura, unlike modern concepts of science, Greek atomism was purely philosophical in nature, with little concern for empirical observations and no concern for chemical experiments. Work, particularly the development of distillation, continued in the early Byzantine period with the most famous practitioner being the 4th century Greek-Egyptian Zosimos of Panopolis. He formulated Boyles law, rejected the four elements and proposed a mechanistic alternative of atoms. Before his work, though, many important discoveries had been made, the Scottish chemist Joseph Black and the Dutchman J. B. English scientist John Dalton proposed the theory of atoms, that all substances are composed of indivisible atoms of matter. Davy discovered nine new elements including the alkali metals by extracting them from their oxides with electric current, british William Prout first proposed ordering all the elements by their atomic weight as all atoms had a weight that was an exact multiple of the atomic weight of hydrogen. The inert gases, later called the noble gases were discovered by William Ramsay in collaboration with Lord Rayleigh at the end of the century, thereby filling in the basic structure of the table. Organic chemistry was developed by Justus von Liebig and others, following Friedrich Wöhlers synthesis of urea which proved that organisms were, in theory
2.
Electron
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The electron is a subatomic particle, symbol e− or β−, with a negative elementary electric charge. Electrons belong to the first generation of the lepton particle family, the electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the include a intrinsic angular momentum of a half-integer value, expressed in units of the reduced Planck constant. As it is a fermion, no two electrons can occupy the same state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of particles and waves, they can collide with other particles and can be diffracted like light. Since an electron has charge, it has an electric field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law, electrons radiate or absorb energy in the form of photons when they are accelerated. Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields, special telescopes can detect electron plasma in outer space. Electrons are involved in applications such as electronics, welding, cathode ray tubes, electron microscopes, radiation therapy, lasers, gaseous ionization detectors. Interactions involving electrons with other particles are of interest in fields such as chemistry. The Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without, allows the composition of the two known as atoms, ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the cause of chemical bonding. In 1838, British natural philosopher Richard Laming first hypothesized the concept of a quantity of electric charge to explain the chemical properties of atoms. Irish physicist George Johnstone Stoney named this charge electron in 1891, electrons can also participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of isotopes and in high-energy collisions. The antiparticle of the electron is called the positron, it is identical to the electron except that it carries electrical, when an electron collides with a positron, both particles can be totally annihilated, producing gamma ray photons. The ancient Greeks noticed that amber attracted small objects when rubbed with fur, along with lightning, this phenomenon is one of humanitys earliest recorded experiences with electricity. In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electricus, both electric and electricity are derived from the Latin ēlectrum, which came from the Greek word for amber, ἤλεκτρον
3.
Heterolysis (chemistry)
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In chemistry, heterolysis or heterolytic fission is the process of cleaving a covalent bond where one previously bonded species takes both original bonding electrons from the other species. During heterolytic bond cleavage of a molecule, a cation. Most commonly the more electronegative atom keeps the pair of electrons becoming anionic while the more electropositive atom becomes cationic, heterolytic fission almost always happens to single bonds, the process usually produces 2 fragment species. This became the model for a covalent bond, in 1932 Linus Pauling first proposed the concept of electronegativity, which also introduced the idea that electrons in a covalent bond may not be shared evenly between the bonded atoms. The rate of reaction for many reactions involving unimolecular heterolysis depends heavily on rate of ionization of the covalent bond, the limiting reaction step is generally the formation of ion pairs. One group in the Ukraine did a study on the role of nucleophilic solvation. They found that the rate of heterolysis depends strongly on the nature of the solvent, a change of reaction medium from hexane to water increases the rate of t-BuCl heterolysis by 14 orders of magnitude. This is caused by very strong solvation of the transition state, the main factors that affect heterolysis rates are mainly the solvent’s polarity and electrophilic as well as its ionizing power. The polarizability, nucleophilicity and cohesion of the solvent had a weaker effect on heterolysis. IUPAC, Compendium of Chemical Terminology, 2nd ed. Online corrected version, blanksby, S. J. Ellison, G. B. Bond Dissociation Energies of Organic Molecules, journal of the American Chemical Society. The Nature of the Chemical Bond, the Energy of Single Bonds and the Relative Electronegativity of Atoms. Journal of the American Chemical Society, dvorko, G. F. Ponomareva, E. A. and Ponomarev, M. E. Role of nucleophilic solvation and the mechanism of covalent bond heterolysis. Abraham MH, Doherty RM, Kamlet JM, Harris JM, armentrout, P. B. and Jack Simons
4.
Ion
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An ion is an atom or a molecule in which the total number of electrons is not equal to the total number of protons, giving the atom or molecule a net positive or negative electrical charge. Ions can be created, by chemical or physical means. In chemical terms, if an atom loses one or more electrons. If an atom gains electrons, it has a net charge and is known as an anion. Ions consisting of only a single atom are atomic or monatomic ions, because of their electric charges, cations and anions attract each other and readily form ionic compounds, such as salts. In the case of ionization of a medium, such as a gas, which are known as ion pairs are created by ion impact, and each pair consists of a free electron. The word ion comes from the Greek word ἰόν, ion, going and this term was introduced by English physicist and chemist Michael Faraday in 1834 for the then-unknown species that goes from one electrode to the other through an aqueous medium. Faraday also introduced the words anion for a charged ion. In Faradays nomenclature, cations were named because they were attracted to the cathode in a galvanic device, arrhenius explanation was that in forming a solution, the salt dissociates into Faradays ions. Arrhenius proposed that ions formed even in the absence of an electric current, ions in their gas-like state are highly reactive, and do not occur in large amounts on Earth, except in flames, lightning, electrical sparks, and other plasmas. These gas-like ions rapidly interact with ions of charge to give neutral molecules or ionic salts. These stabilized species are commonly found in the environment at low temperatures. A common example is the present in seawater, which are derived from the dissolved salts. Electrons, due to their mass and thus larger space-filling properties as matter waves, determine the size of atoms. Thus, anions are larger than the parent molecule or atom, as the excess electron repel each other, as such, in general, cations are smaller than the corresponding parent atom or molecule due to the smaller size of its electron cloud. One particular cation contains no electrons, and thus consists of a single proton - very much smaller than the parent hydrogen atom. Since the electric charge on a proton is equal in magnitude to the charge on an electron, an anion, from the Greek word ἄνω, meaning up, is an ion with more electrons than protons, giving it a net negative charge. A cation, from the Greek word κατά, meaning down, is an ion with fewer electrons than protons, there are additional names used for ions with multiple charges
5.
Sulfonate
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A sulfonate is a salt or ester of a sulfonic acid. It contains the functional group R-SO3−, anions with the general formula RSO3− are called sulfonates. They are the bases of sulfonic acids with formula RSO2OH. As sulfonic acids tend to be acids, the corresponding sulfonates are weak bases. Due to the stability of sulfonate anions, the cations of sulfonate salts such as scandium triflate have application as Lewis acids, a classic organic reaction for the preparation of sulfonates is that of alkyl halides with sulfites such as sodium sulfite, first described by Adolph Strecker in 1868. The general reaction is, RX + M2SO3 → RSO3M + MX Iodide is used as a catalyst, esters with the general formula R1SO2OR2 are called sulfonic esters. Individual members of the category are named analogously to how ordinary carboxyl esters are named, for example, if the R2 group is a methyl group and the R1 group is a trifluoromethyl group, the resulting compound is methyl trifluoromethanesulfonate. Sulfonic esters are used as reagents in organic synthesis, chiefly because the RSO3− group is a leaving group. Methyl triflate, for example, is a methylating reagent. Sulfonates are commonly used to confer water solubility to protein crosslinkers such as N-hydroxysulfosuccinimide, BS3, Sulfo-SMCC, cyclic sulfonic esters are called sultones. Some sultones are short-lived intermediates, used as alkylating agents to introduce a negatively charged sulfonate group. In the presence of water, they hydrolyze to the hydroxy sulfonic acids. Sultone oximes are key intermediates in the synthesis of the anti-convulsant drug zonisamide, tisocromide is an example of a sultone. Mesylate, CH3SO3− Triflate, CF3SO3− Ethanesulfonate, C2H5SO3− Tosylate, CH3C6H4SO3− Benzenesulfonic acid, C6H5SO3− Closilate, ClC6H4SO3− Camphorsulfonate, SO3− Sulfate Sulfoxide Sulfonyl
6.
Tosyl
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This group is usually derived from the compound tosyl chloride, CH3C6H4SO2Cl, which forms esters and amides of toluenesulfonic acid. The para orientation illustrated is most common, and by convention tosyl refers to the p-toluenesulfonyl group, tosylate refers to the anion of p-toluenesulfonic acid and it is abbreviated as TsO−, or it may refer to esters of p-toluenesulfonic acid. For SN2 reactions, alkyl alcohols can also be converted to alkyl tosylates, in this reaction, the lone pair of the alcohol oxygen attacks the sulfur of the tosyl chloride, kicking off the chloride group and forming the tosylate with retention of reactant stereochemistry. This is useful because alcohols are poor leaving groups in SN2 reactions and it is the transformation of alkyl alcohols to alkyl tosylates that allows an SN2 reaction to occur in the presence of a good nucleophile. A tosyl group can function as a group in organic synthesis. Alcohols can be converted to groups so that they do not react. The tosylate group may later be converted back into an alcohol, the latter is a leaving group for displacement by diisopropylamine, The tosyl group is also useful as a protecting group for amines. The resulting sulfonamide structure is extremely stable and it can be deprotected to reveal the amine using reductive or strongly acidic conditions. Tosyl group is used as a protecting group for amines in organic synthesis. Tosyl chloride and pyridine in dichloromethane HBr and acetic acid at 70 °C Refluxing with TMSCl, sodium iodide, there are p-nitrobenzenesulfonates and p-bromobenzenesulfonates, respectively
7.
Sarin
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Sarin, or GB, is a colorless, odorless liquid, used as a chemical weapon owing to its extreme potency as a nerve agent. It is generally considered a weapon of mass destruction, production and stockpiling of sarin was outlawed as of April 1997 by the Chemical Weapons Convention of 1993, and it is classified as a Schedule 1 substance. In June 1994, the UN Special Commission on Iraqi disarmament destroyed the nerve agent sarin under Security Council resolution 687 concerning the disposal of Iraqs weapons of mass destruction, Sarin is an organophosphorus compound with the formula CH3PF. People who absorb a non-lethal dose, but do not receive medical treatment. Sarin is a molecule because it has four chemically distinct substituents attached to the tetrahedral phosphorus center. The SP form is the active enantiomer due to its greater binding affinity to acetylcholinesterase. The P-F bond is broken by nucleophilic agents, such as water. At high pH, sarin decomposes rapidly to nontoxic phosphonic acid derivatives and it is usually manufactured and weaponized as a racemic mixture—an equal mixture of both enantiomeric forms, as this is a simpler process and provides an adequate weapon. A number of pathways can be used to create sarin. The final reaction typically involves attachment of the group to the phosphorus with an alcoholysis with isopropyl alcohol. Two variants of this process are common and this reaction also gives sarin, but hydrochloric acid as a byproduct instead. The Di-Di process was used by the United States for the production of its unitary sarin stockpile, the scheme below describes an example of Di-Di process. The selection of reagents is arbitrary and reaction conditions and product yield depend on the selected reagents, inert atmosphere and anhydrous conditions are used for synthesis of sarin and other organophosphates. As both reactions leave considerable acid in the product, bulk sarin produced without further treatment has a poor shelf life. Various methods have been tried to resolve these problems, triethylamine was added to UK sarin, with relatively poor success. The Aum Shinrikyo cult experimented with triethylamine as well, N, N-Diethylaniline was used by Aum Shinrikyo for acid reduction. N, N′-Diisopropylcarbodimide was added to sarin produced at Rocky Mountain Arsenal to combat corrosion, isopropylamine was included as part of the M687 155mm field artillery shell, which was a binary sarin weapon system developed by the US Army. Another byproduct of these two processes is diisopropyl methylphosphonate, formed when a second isopropyl alcohol reacts with the sarin itself
8.
Water
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Water is a transparent and nearly colorless chemical substance that is the main constituent of Earths streams, lakes, and oceans, and the fluids of most living organisms. Its chemical formula is H2O, meaning that its molecule contains one oxygen, Water strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure, but it often refers also to its solid state or its gaseous state. It also occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew, aquifers, Water covers 71% of the Earths surface. It is vital for all forms of life. Only 2. 5% of this water is freshwater, and 98. 8% of that water is in ice and groundwater. Less than 0. 3% of all freshwater is in rivers, lakes, and the atmosphere, a greater quantity of water is found in the earths interior. Water on Earth moves continually through the cycle of evaporation and transpiration, condensation, precipitation. Evaporation and transpiration contribute to the precipitation over land, large amounts of water are also chemically combined or adsorbed in hydrated minerals. Safe drinking water is essential to humans and other even though it provides no calories or organic nutrients. There is a correlation between access to safe water and gross domestic product per capita. However, some observers have estimated that by 2025 more than half of the population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in developing regions of the world. Water plays an important role in the world economy, approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers, lakes, large quantities of water, ice, and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a variety of chemical substances, as such it is widely used in industrial processes. Water is also central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, surfing, sport fishing, Water is a liquid at the temperatures and pressures that are most adequate for life. Specifically, at atmospheric pressure of 1 bar, water is a liquid between the temperatures of 273.15 K and 373.15 K
9.
Nitration
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Nitration is a general class of chemical process for the introduction of a nitro group into an organic chemical compound. More loosely the term also is applied incorrectly to the different process of forming nitrate esters between alcohols and nitric acid, as occurs in the synthesis of nitroglycerin. There are many industrial applications of nitration in the strict sense. Nitration reactions are used for the production of explosives, for example the conversion of guanidine to nitroguanidine. However, they are of importance as chemical intermediates and precursors. Millions of tons of nitroaromatics are produced annually, typical nitration syntheses apply so-called mixed acid, a mixture of concentrated nitric acid and sulfuric acids. This mixture produces the nitronium ion, which is the species in aromatic nitration. This active ingredient, which can be isolated in the case of nitronium tetrafluoroborate, in mixed-acid syntheses sulfuric acid is not consumed and hence acts as a catalyst as well as an absorbent for water. In the case of nitration of benzene, the reaction is conducted at 50 °C, selectivity can be a challenge in nitrations because as a rule more than one compound may result but only one is desired, so alternative products act as contaminants or are simply wasted. Accordingly, it is desirable to design syntheses with suitable selectivity, for example, by controlling the reaction conditions, the substituents on aromatic rings affect the rate of this electrophilic aromatic substitution. Deactivating groups such as nitro groups have an electron-withdrawing effect. Such groups deactivate the reaction and directs the electrophilic nitronium ion to attack the aromatic meta position, deactivating meta-directing substituents include sulfonyl, cyano groups, keto, esters, and carboxylates. Nitration can be accelerated by activating groups such as amino, hydroxy and methyl groups also amides and ethers resulting in para, the direct nitration of aniline with nitric acid and sulfuric acid, according to one source results in a 50/50 mixture of para and meta nitroaniline. In this reaction the fast-reacting and activating aniline exists in equilibrium with the abundant but less reactive anilinium ion. According to another source a more controlled nitration of aniline starts with the formation of acetanilide by reaction with acetic anhydride followed by the actual nitration, because the amide is a regular activating group the products formed are the para and ortho isomers. Heating the reaction mixture is sufficient to hydrolyze the amide back to the nitrated aniline, in the Wolfenstein-Boters reaction, benzene reacts with nitric acid and mercury nitrate to give picric acid
10.
Benzene
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Benzene is an important organic chemical compound with the chemical formula C6H6. The benzene molecule is composed of 6 carbon atoms joined in a ring with 1 hydrogen atom attached to each, because it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon. Benzene is a constituent of crude oil and is one of the elementary petrochemicals. Because of the cyclic continuous pi bond between the atoms, benzene is classed as an aromatic hydrocarbon, the second -annulene. Benzene is a colorless and highly flammable liquid with a sweet smell and it is used primarily as a precursor to the manufacture of chemicals with more complex structure, such as ethylbenzene and cumene, of which billions of kilograms are produced. Because benzene has a high number, it is an important component of gasoline. Because benzene is a carcinogen, most non-industrial applications have been limited. The word benzene derives historically from gum benzoin, a resin known to European pharmacists. An acidic material was derived from benzoin by sublimation, and named flowers of benzoin, the hydrocarbon derived from benzoic acid thus acquired the name benzin, benzol, or benzene. Michael Faraday first isolated and identified benzene in 1825 from the oily residue derived from the production of illuminating gas, in 1833, Eilhard Mitscherlich produced it by distilling benzoic acid and lime. He gave the compound the name benzin, in 1845, Charles Mansfield, working under August Wilhelm von Hofmann, isolated benzene from coal tar. Four years later, Mansfield began the first industrial-scale production of benzene, gradually, the sense developed among chemists that a number of substances were chemically related to benzene, comprising a diverse chemical family. In 1855, Hofmann used the word aromatic to designate this family relationship, in 1997, benzene was detected in deep space. The empirical formula for benzene was known, but its highly polyunsaturated structure. In 1865, the German chemist Friedrich August Kekulé published a paper in French suggesting that the structure contained a ring of six carbon atoms with alternating single and double bonds, the next year he published a much longer paper in German on the same subject. Kekulés symmetrical ring could explain these facts, as well as benzenes 1,1 carbon-hydrogen ratio. Here Kekulé spoke of the creation of the theory and he said that he had discovered the ring shape of the benzene molecule after having a reverie or day-dream of a snake seizing its own tail. This vision, he said, came to him years of studying the nature of carbon-carbon bonds
11.
Transition state theory
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Transition state theory explains the reaction rates of elementary chemical reactions. The theory assumes a special type of equilibrium between reactants and activated transition state complexes. TST is used primarily to understand qualitatively how chemical reactions take place and this theory was developed simultaneously in 1935 by Henry Eyring, then at Princeton University, and by Meredith Gwynne Evans and Michael Polanyi of the University of Manchester. TST is also referred to as theory, absolute-rate theory. Before the development of TST, the Arrhenius rate law was used to determine energies for the reaction barrier. Therefore, further development was necessary to understand the two associated with this law, the pre-exponential factor and the activation energy. During that period, many scientists and researchers contributed significantly to the development of the theory, the basic ideas behind transition state theory are as follows, Rates of reaction can be studied by examining activated complexes near the saddle point of a potential energy surface. The details of how these complexes are formed are not important, the saddle point itself is called the transition state. The activated complexes are in an equilibrium with the reactant molecules. The activated complexes can convert into products, and kinetic theory can be used to calculate the rate of this conversion, by the early 20th century many had accepted the Arrhenius equation, but the physical interpretation of A and Ea remained vague. In 1910, French chemist René Marcelin introduced the concept of standard Gibbs energy of activation and they proposed the following rate constant equation k ∝ exp exp However, the nature of the constant was still unclear. In early 1900, Max Trautz and William Lewis studied the rate of the reaction using collision theory, Lewis applied his treatment to the following reaction and obtained good agreement with experimental result. 2HI → H2 + I2 However, later when the treatment was applied to other reactions. Statistical mechanics played a significant role in the development of TST and it was not until 1912 when the French chemist A. Berthoud used the Maxwell–Boltzmann distribution law to obtain an expression for the rate constant. D ln k d T = a − b T R T2 where a and b are constants related to energy terms. Two years later, René Marcelin made a contribution by treating the progress of a chemical reaction as a motion of a point in phase space. He then applied Gibbs statistical-mechanical procedures and obtained a similar to the one he had obtained earlier from thermodynamic consideration. In 1915, another important contribution came from British physicist James Rice, based on his statistical analysis, he concluded that the rate constant is proportional to the critical increment
12.
Acid dissociation constant
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An acid dissociation constant, Ka, is a quantitative measure of the strength of an acid in solution. It is the constant for a chemical reaction known as dissociation in the context of acid–base reactions. In the example shown in the figure, HA represents acetic acid, and A− represents the acetate ion, the chemical species HA, A− and H3O+ are said to be in equilibrium when their concentrations do not change with the passing of time. The definition can then be more simply H A ⇌ A − + H +, K a = This is the definition in common usage. A weak acid has a pKa value in the approximate range −2 to 12 in water, pKa values for strong acids can, however, be estimated by theoretical means. The definition can be extended to non-aqueous solvents, such as acetonitrile and dimethylsulfoxide. Denoting a solvent molecule by S H A + S ⇌ A − + S H +, K a = When the concentration of solvent molecules can be taken to be constant, K a =, as before. The value of pKa also depends on structure of the acid in many ways. For example, Pauling proposed two rules, one for successive pKa of polyprotic acids, and one to estimate the pKa of oxyacids based on the number of =O and −OH groups. Other structural factors that influence the magnitude of the dissociation constant include inductive effects, mesomeric effects. Hammett type equations have frequently applied to the estimation of pKa. The quantitative behaviour of acids and bases in solution can be only if their pKa values are known. These calculations find application in different areas of chemistry, biology, medicine. Acid dissociation constants are essential in aquatic chemistry and chemical oceanography. In living organisms, acid–base homeostasis and enzyme kinetics are dependent on the pKa values of the acids and bases present in the cell. According to Arrheniuss original definition, an acid is a substance that dissociates in solution, releasing the hydrogen ion H+. The equilibrium constant for this reaction is known as a dissociation constant. Brønsted and Lowry generalised this further to an exchange reaction
13.
Conjugate acid
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A conjugate acid, within the Brønsted–Lowry acid–base theory, is a species formed by the reception of a proton by a base—in other words, it is a base with a hydrogen ion added to it. On the other hand, a base is merely what is left after an acid has donated a proton in a chemical reaction. Hence, a base is a species formed by the removal of a proton from an acid. A proton is a particle with a unit positive electrical charge, it is represented by the symbol H+ because it constitutes the nucleus of a hydrogen atom, that is. A cation can be an acid, and an anion can be a conjugate base, depending on which substance is involved. In an acid-base reaction, an acid plus a base reacts to form a conjugate base plus a conjugate acid, refer to the following figure, We say that the water molecule is the conjugate acid of the hydroxide ion after the latter received the hydrogen proton donated by ammonium. On the other hand, ammonia is the base for the acid ammonium after ammonium has donated a hydrogen ion towards the production of the water molecule. The strength of an acid is directly proportional to its dissociation constant. If a conjugate acid is strong, its dissociation will have an equilibrium constant. The strength of a base can be seen as the tendency of the species to pull hydrogen protons towards itself. If a conjugate base is classified as strong, it will hold on to the hydrogen proton when in solution, if a chemical species is classified as a weak acid, its conjugate base will be strong in nature. This can be observed in ammonias reaction with water, the reaction proceeds until most of the ammonia has been transformed to ammonium. This shift to the right in the equilibrium of the reaction means that ammonium does not dissociate easily in water. On the other hand, if a species is classified as a strong acid, an example of this case would be the dissociation of Hydrochloric acid HCl in water. Since HCl is an acid, its conjugate base will be a weak conjugate base. Therefore, in system, most H+ will be in the form of a Hydronium ion H 3O+ instead of attached to a Cl anion. To summarize, the stronger the acid or base, the weaker the conjugate, the acid and conjugate base as well as the base and conjugate acid are known as conjugate pairs. When finding a conjugate acid or base, it is important to look at the reactants of the chemical equation, to identify the conjugate acid, look for the pair of compounds that are related
14.
Nitrogen
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Nitrogen is a chemical element with symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772, although Carl Wilhelm Scheele and Henry Cavendish had independently done so at about the same time, Rutherford is generally accorded the credit because his work was published first. Nitrogen is the lightest member of group 15 of the periodic table, the name comes from the Greek πνίγειν to choke, directly referencing nitrogens asphyxiating properties. It is an element in the universe, estimated at about seventh in total abundance in the Milky Way. At standard temperature and pressure, two atoms of the element bind to form dinitrogen, a colourless and odorless diatomic gas with the formula N2, dinitrogen forms about 78% of Earths atmosphere, making it the most abundant uncombined element. Nitrogen occurs in all organisms, primarily in amino acids, in the nucleic acids, the human body contains about 3% nitrogen by mass, the fourth most abundant element in the body after oxygen, carbon, and hydrogen. The nitrogen cycle describes movement of the element from the air, into the biosphere and organic compounds, many industrially important compounds, such as ammonia, nitric acid, organic nitrates, and cyanides, contain nitrogen. The extremely strong bond in elemental nitrogen, the second strongest bond in any diatomic molecule. Synthetically produced ammonia and nitrates are key industrial fertilisers, and fertiliser nitrates are key pollutants in the eutrophication of water systems. Apart from its use in fertilisers and energy-stores, nitrogen is a constituent of organic compounds as diverse as Kevlar used in high-strength fabric, Nitrogen is a constituent of every major pharmacological drug class, including antibiotics. Many notable nitrogen-containing drugs, such as the caffeine and morphine or the synthetic amphetamines. Nitrogen compounds have a long history, ammonium chloride having been known to Herodotus. They were well known by the Middle Ages, alchemists knew nitric acid as aqua fortis, as well as other nitrogen compounds such as ammonium salts and nitrate salts. The mixture of nitric and hydrochloric acids was known as aqua regia, celebrated for its ability to dissolve gold, the discovery of nitrogen is attributed to the Scottish physician Daniel Rutherford in 1772, who called it noxious air. Though he did not recognise it as a different chemical substance, he clearly distinguished it from Joseph Blacks fixed air. The fact that there was a component of air that does not support combustion was clear to Rutherford, Nitrogen was also studied at about the same time by Carl Wilhelm Scheele, Henry Cavendish, and Joseph Priestley, who referred to it as burnt air or phlogisticated air. Nitrogen gas was inert enough that Antoine Lavoisier referred to it as air or azote, from the Greek word άζωτικός. In an atmosphere of nitrogen, animals died and flames were extinguished
15.
Ether
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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
16.
Triflate
–
Trifluoromethanesulfonate, also known by the trivial name triflate, is a functional group with the formula CF3SO3−. The triflate group is represented by −OTf, as opposed to −Tf. For example, n-butyl triflate can be written as CH3CH2CH2CH2OTf, the corresponding triflate anion, CF 3SO−3, is an extremely stable polyatomic ion, being the conjugate base of triflic acid, one of the strongest acids known. It is defined as a superacid, because it is more acidic than sulfuric acid. A triflate group is an excellent leaving group used in organic reactions such as nucleophilic substitution, Suzuki couplings. Since alkyl triflates are extremely reactive in SN2 reactions, they must be stored in free of nucleophiles. The anion owes its stability to resonance stabilization which causes the charge to be spread over the three oxygen atoms and the sulfur atom. An additional stabilization is achieved by the group as a strong electron-withdrawing group. Triflates have also applied as ligands for group 11 and 13 metals along with lanthanides. Lithium triflates are used in lithium ion batteries as a component of the electrolyte. A mild triflating reagent is phenyl triflimide or N, N-bisaniline, Triflate salts are thermally very stable with melting points up to 350 °C for sodium, boron and silver salts especially in water-free form. They can be obtained directly from triflic acid and the hydroxide or metal carbonate in water. Especially useful are the lanthanide triflates of the type Ln3, a related popular catalyst scandium triflate is used in such reactions as aldol reactions and Diels-Alder reactions. An example is the Mukaiyama aldol addition reaction between benzaldehyde and the enol ether of cyclohexanone with an 81% chemical yield. The corresponding reaction with the yttrium salt fails, Triflate is a commonly used counterion for organometallic complexes, methyl triflate Nonaflate Trifluoromethanesulfonic acid Metal triflimidate Comins reagent
17.
Tosylate
–
This group is usually derived from the compound tosyl chloride, CH3C6H4SO2Cl, which forms esters and amides of toluenesulfonic acid. The para orientation illustrated is most common, and by convention tosyl refers to the p-toluenesulfonyl group, tosylate refers to the anion of p-toluenesulfonic acid and it is abbreviated as TsO−, or it may refer to esters of p-toluenesulfonic acid. For SN2 reactions, alkyl alcohols can also be converted to alkyl tosylates, in this reaction, the lone pair of the alcohol oxygen attacks the sulfur of the tosyl chloride, kicking off the chloride group and forming the tosylate with retention of reactant stereochemistry. This is useful because alcohols are poor leaving groups in SN2 reactions and it is the transformation of alkyl alcohols to alkyl tosylates that allows an SN2 reaction to occur in the presence of a good nucleophile. A tosyl group can function as a group in organic synthesis. Alcohols can be converted to groups so that they do not react. The tosylate group may later be converted back into an alcohol, the latter is a leaving group for displacement by diisopropylamine, The tosyl group is also useful as a protecting group for amines. The resulting sulfonamide structure is extremely stable and it can be deprotected to reveal the amine using reductive or strongly acidic conditions. Tosyl group is used as a protecting group for amines in organic synthesis. Tosyl chloride and pyridine in dichloromethane HBr and acetic acid at 70 °C Refluxing with TMSCl, sodium iodide, there are p-nitrobenzenesulfonates and p-bromobenzenesulfonates, respectively
18.
Mesylate
–
In chemistry, a mesylate is any salt or ester of methanesulfonic acid. In salts, the mesylate is present as the CH3SO3− anion, when modifying the International Nonproprietary Name of a pharmaceutical substance containing the group or anion, the correct spelling is mesilate. Mesylate esters are a group of compounds that share a common functional group with the general structure CH3SO2O–R, abbreviated MsO–R. Mesylate is considered a group in nucleophilic substitution reactions. Mesylates are generally prepared by treating an alcohol and methanesulfonyl chloride in the presence of a base, related to mesylate, is the mesyl, an abbreviation for methanesulfonyl or CH3SO2 functional group. For example, methanesulfonyl chloride is often referred to as mesyl chloride, whereas mesylates are often hydrolytically labile, mesyl groups, when attached to nitrogen are robust with respect to hydrolysis. This functional group appears in a variety of medications, particularly cardiac, examples include Sotalol, ibutilide, sematilide, Dronedarone, Dofetilide, E-4031, and Bitopertin. Ice core samples from a spot in Antarctica were found to have tiny inclusions of magnesium methanesulfonate dodecahydrate. This natural phase is recognized as the mineral ernstburkeite
19.
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
20.
Chloride
–
The chloride ion /ˈklɔəraɪd/ is the anion Cl−. It is formed when the element chlorine gains an electron or when a compound such as chloride is dissolved in water or other polar solvents. Chloride salts such as sodium chloride are often soluble in water. It is an essential electrolyte located in all body fluids responsible for maintaining acid/base balance, transmitting nerve impulses and regulating fluid in, less frequently, the word chloride may also form part of the common name of chemical compounds in which one or more chlorine atoms are covalently bonded. For example, methyl chloride, with the standard name chloromethane is a compound with a covalent C−Cl bond in which the chlorine is not an anion. A chloride ion is much larger than an atom,167 and 99 pm. The ion is colorless and diamagnetic, in aqueous solution, it is highly soluble in most cases, however, some chloride salts, such as silver chloride, lead chloride, and mercury chloride are slightly soluble in water. In aqueous solution, chloride is bound by the end of the water molecules. Some chloride-containing minerals include the chlorides of sodium, potassium, and magnesium, called serum chloride, the concentration of chloride in the blood is regulated by the kidneys. A chloride ion is a component of some proteins, e. g. it is present in the amylase enzyme. The chlor-alkali industry is a consumer of the worlds energy budget. This process converts sodium chloride into chlorine and sodium hydroxide, which are used to make many other materials and chemicals, in the petroleum industry, the chlorides are a closely monitored constituent of the mud system. An increase of the chlorides in the mud system may be an indication of drilling into a high-pressure saltwater formation and its increase can also indicate the poor quality of a target sand. Chloride is also a useful and reliable chemical indicator of river / groundwater fecal contamination, as chloride is a non-reactive solute, many water regulating companies around the world utilize chloride to check the contamination levels of the rivers and potable water sources. Chloride salts such as sodium chloride are used to preserve food, chloride is an essential electrolyte, trafficking in and out of cells through chloride channels and playing a key role in maintaining cell homeostasis and transmitting action potentials in neurons. Characteristic concentrations of chloride in model organisms are, in both E. coli and budding yeast are 10-200mM, in mammalian cell 5-100mM and in blood plasma 100mM, chloride can be oxidized but not reduced. The first oxidation, as employed in the process, is conversion to chlorine gas. Chlorine can be oxidized to other oxides and oxyanions including hypochlorite, chlorine dioxide, chlorate
21.
Nitrate
–
Nitrate is a polyatomic ion with the molecular formula NO−3 and a molecular mass of 62.0049 g/mol. Nitrates also describe the functional group RONO2. These nitrate esters are a class of explosives. The anion is the 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 charge of −1. This arrangement is used as an example of resonance. Like the isoelectronic carbonate ion, the ion can be represented by resonance structures. A common example of a nitrate salt is potassium nitrate. A rich source of nitrate in the human body comes from diets rich in leafy green foods, such as spinach. NO3- is the active component within beetroot juice and other vegetables. Nitrite and water are converted in the body to nitric oxide, nitrate salts are found naturally on earth as large deposits, particularly of nitratine, a major source of sodium nitrate. Nitrates are found in man-made fertilizers, as a byproduct of lightning strikes in earths nitrogen-oxygen rich atmosphere, nitric acid is produced when nitrogen dioxide reacts with water vapor. Nitrates are mainly produced for use as fertilizers in agriculture because of their solubility and biodegradability. The main nitrate fertilizers are ammonium, sodium, potassium, 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 oxidation of carbon compounds liberates large volumes of gases. Sodium nitrate is used to air bubbles from molten glass. Mixtures of the salt are used to harden some metals. Explosives and table tennis balls are made from celluloid, 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
22.
Thioether
–
A thioether is a functional group in organosulfur chemistry with the connectivity C–S–C as shown on right. Like many other sulfur-containing compounds, volatile thioethers have foul odors, a thioether is similar to an ether except that it contains a sulfur atom in place of the oxygen. The grouping of oxygen and sulfur in the table suggests that the chemical properties of ethers and thioethers are somewhat similar. Thioethers are sometimes called sulfides, especially in the older literature, the two organic substituents are indicated by the prefixes. Some thioethers are named by modifying the name for the corresponding ether. For example, C6H5SCH3 is methyl phenyl sulfide, but is commonly called thioanisole, since its structure is related to that for anisole. Thioether is a functional group, the C–S–C angle approaching 90°. The C–S bonds are about 180 pm, thioethers are characterized by their strong odors, which are similar to thiol odor. This odor limits the applications of volatile thioethers, in terms of their physical properties they resemble ethers but are less volatile, higher melting, and less hydrophilic. These properties follow from the polarizability of the divalent sulfur center, thiophenes are a special class of thioether-containing heterocyclic compounds. Because of their character, they are non-nucleophilic. The nonbonding electrons on sulfur are delocalized into the π-system, as a consequence, thiophene exhibits few properties expected for a thioether – thiophene is non-nucleophilic at sulfur and, in fact, is sweet-smelling. Upon hydrogenation, thiophene gives tetrahydrothiophene, C4H8S, which indeed does behave as a typical thioether, thioethers are important in biology, notably in the amino acid methionine and the cofactor biotin. Petroleum contains many organosulfur compounds, including thioethers. Polyphenylene sulfide is a high temperature plastic. Coenzyme M, CH 3SCH 2CH 2SO−3, is the precursor to methane via the process of methanogenesis, analogously, the reaction of disulfides with organolithium reagents produces thioethers, R3CLi + R1S–SR2 → R3CSR1 + R2SLi Analogous reactions are known starting with Grignard reagents. Alternatively, thioethers can be synthesized by the addition of a thiol to an alkene, thioethers can also be prepared by many other methods, such as the Pummerer rearrangement. For example, S-adenosylmethionine acts as an agent in biological SN2 reactions. While, in general, ethers are non-oxidizable, thioethers can be oxidized to the sulfoxides
23.
Amine
–
In organic chemistry, amines are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group, important amines include amino acids, biogenic amines, trimethylamine, and aniline, see Category, Amines for a list of amines. Inorganic derivatives of ammonia are also called amines, such as chloramine, see Category, compounds with a nitrogen atom attached to a carbonyl group, thus having the structure R–CO–NR′R″, are called amides and have different chemical properties from amines. An aliphatic amine has no aromatic ring attached directly to the nitrogen atom, aromatic amines have the nitrogen atom connected to an aromatic ring as in the various anilines. The aromatic ring decreases the alkalinity of the amine, depending on its substituents, the presence of an amine group strongly increases the reactivity of the aromatic ring, due to an electron-donating effect. Amines are organized into four subcategories, Primary amines — Primary amines arise when one of three atoms in ammonia is replaced by an alkyl or aromatic. Important primary alkyl amines include, methylamine, most amino acids, Secondary amines — Secondary amines have two organic substituents bound to the nitrogen together with one hydrogen. Important representatives include dimethylamine, while an example of an aromatic amine would be diphenylamine, tertiary amines — In tertiary amines, nitrogen has three organic substituents. Examples include trimethylamine, which has a fishy smell. Cyclic amines — Cyclic amines are either secondary or tertiary amines, examples of cyclic amines include the 3-membered ring aziridine and the six-membered ring piperidine. N-methylpiperidine and N-phenylpiperidine are examples of tertiary amines. It is also possible to have four organic substituents on the nitrogen and these species are not amines but are quaternary ammonium cations and have a charged nitrogen center. Quaternary ammonium salts exist with many kinds of anions, Amines are named in several ways. Typically, the compound is given the prefix amino- or the suffix, the prefix N- shows substitution on the nitrogen atom. An organic compound with multiple amino groups is called a diamine, triamine, tetraamine, systematic names for some common amines, Hydrogen bonding significantly influences the properties of primary and secondary amines. Thus the melting point and boiling point of amines is higher than those of the corresponding phosphines, for example, methyl and ethyl amines are gases under standard conditions, whereas the corresponding methyl and ethyl alcohols are liquids. Amines possess a characteristic smell, liquid amines have a distinctive fishy smell. The nitrogen atom features a lone pair that can bind H+ to form an ammonium ion R3NH+
24.
Carboxylic acid
–
A carboxylic acid /ˌkɑːrbɒkˈsɪlɪk/ is an organic compound that contains a carboxyl group. The general formula of an acid is R–COOH, with R referring to the rest of the molecule. Carboxylic acids occur widely and include the amino acids and acetic acid, salts and esters of carboxylic acids are called carboxylates. When a carboxyl group is deprotonated, its conjugate base forms a carboxylate anion, carboxylate ions are resonance-stabilized, and this increased stability makes carboxylic acids more acidic than alcohols. Carboxylic acids can be seen as reduced or alkylated forms of the Lewis acid carbon dioxide, carboxylic acids are commonly identified using their trivial names, and usually have the suffix -ic acid. IUPAC-recommended names also exist, in system, carboxylic acids have an -oic acid suffix. For example, butyric acid is butanoic acid by IUPAC guidelines, the -oic acid nomenclature detail is based on the name of the previously-known chemical benzoic acid. Alternately, it can be named as a carboxy or carboxylic acid substituent on another parent structure, for example, 2-carboxyfuran. The carboxylate anion of an acid is usually named with the suffix -ate, in keeping with the general pattern of -ic acid and -ate for a conjugate acid and its conjugate base. For example, the base of acetic acid is acetate. The radical •COOH has only a fleeting existence. The acid dissociation constant of •COOH has been measured using electron paramagnetic resonance spectroscopy, the carboxyl group tends to dimerise to form oxalic acid. Because they are both hydrogen-bond acceptors and hydrogen-bond donors, they participate in hydrogen bonding. Together the hydroxyl and carbonyl group forms the functional group carboxyl, carboxylic acids usually exist as dimeric pairs in nonpolar media due to their tendency to self-associate. Smaller carboxylic acids are soluble in water, whereas higher carboxylic acids are less due to the increasing hydrophobic nature of the alkyl chain. These longer chain acids tend to be soluble in less-polar solvents such as ethers. Carboxylic acids tend to have higher boiling points than water, not only because of their surface area. Carboxylic acids tend to evaporate or boil as these dimers, for boiling to occur, either the dimer bonds must be broken or the entire dimer arrangement must be vaporised, both of which increase the enthalpy of vaporization requirements significantly
25.
Phenol
–
Phenol, also known as carbolic acid, is an aromatic organic compound with the molecular formula C6H5OH. It is a crystalline solid that is volatile. The molecule consists of a phenyl group bonded to a hydroxyl group and it is mildly acidic and requires careful handling due to its propensity to cause chemical burns. Phenol was first extracted from tar, but today is produced on a large scale from petroleum. It is an important industrial commodity as a precursor to many materials and it is primarily used to synthesize plastics and related materials. Phenol and its derivatives are essential for production of polycarbonates, epoxies, Bakelite, nylon, detergents, herbicides such as phenoxy herbicides. Phenol is appreciably soluble in water, with about 84.2 g dissolving in 1000 mL, homogeneous mixtures of phenol and water at phenol to water mass ratios of ~2.6 and higher are possible. The sodium salt of phenol, sodium phenoxide, is far more water-soluble and it reacts completely with aqueous NaOH to lose H+, whereas most alcohols react only partially. One explanation for the increased acidity over alcohols is resonance stabilization of the anion by the aromatic ring. In this way, the charge on oxygen is delocalized on to the ortho. In another explanation, increased acidity is the result of orbital overlap between the lone pairs and the aromatic system. The pKa of the enol of acetone is 10.9, the acidities of phenol and acetone enol diverge in the gas phase owing to the effects of solvation. About 1⁄3 of the acidity of phenol is attributable to inductive effects. Phenolate esters are more stable toward hydrolysis than acid anhydrides and acyl halides but are sufficiently reactive under mild conditions to facilitate the formation of amide bonds, Phenol exhibits keto-enol tautomerism with its unstable keto tautomer cyclohexadienone, but only a tiny fraction of phenol exists as the keto form. The equilibrium constant for enolisation is approximately 10−13, meaning only one in every ten trillion molecules is in the keto form at any moment. The small amount of stabilisation gained by exchanging a C=C bond for a C=O bond is more than offset by the large destabilisation resulting from the loss of aromaticity, Phenol therefore exists essentially entirely in the enol form. Phenoxides are enolates stabilised by aromaticity, under normal circumstances, phenoxide is more reactive at the oxygen position, but the oxygen position is a hard nucleophile whereas the alpha-carbon positions tend to be soft. Phenol is highly reactive toward electrophilic aromatic substitution as the oxygen atoms pi electrons donate electron density into the ring, by this general approach, many groups can be appended to the ring, via halogenation, acylation, sulfonation, and other processes
26.
Hydroxide
–
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a covalent bond and it is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, the hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Sodium hydroxide is a multi-million-ton per annum commodity chemical, a hydroxide attached to a strongly electropositive center may itself ionize, liberating a hydrogen cation, making the parent compound an acid. The corresponding electrically neutral compound •HO is the hydroxyl radical, the corresponding covalently-bound group –OH of atoms is the hydroxyl group. Hydroxide ion and hydroxyl group are nucleophiles and can act as a catalyst in organic chemistry, many inorganic substances which bear the word hydroxide in their names are not ionic compounds of the hydroxide ion, but covalent compounds which contain hydroxyl groups. The pH of a solution is equal to the decimal cologarithm of the cation concentration. The concentration of ions can be expressed in terms of pOH. Addition of a base to water will reduce the hydrogen cation concentration, POH can be kept at a nearly constant value with various buffer solutions. In aqueous solution the hydroxide ion is a base in the Brønsted–Lowry sense as it can accept a proton from a Brønsted–Lowry acid to form a water molecule and it can also act as a Lewis base by donating a pair of electrons to a Lewis acid. In aqueous solution both hydrogen and hydroxide ions are solvated, with hydrogen bonds between oxygen and hydrogen atoms. Indeed, the bihydroxide ion H 3O−2 has been characterized in the solid state and this compound is centrosymmetric and has a very short hydrogen bond that is similar to the length in the bifluoride ion HF−2. In aqueous solution the hydroxide ion forms strong bonds with water molecules. A consequence of this is that concentrated solutions of sodium hydroxide have high viscosity due to the formation of a network of hydrogen bonds as in hydrogen fluoride solutions. In solution, exposed to air, the ion reacts rapidly with atmospheric carbon dioxide, acting as an acid, to form, initially. OH− + CO2 ⇌ HCO−3 The equilibrium constant for this reaction can be specified either as a reaction with dissolved carbon dioxide or as a reaction with carbon dioxide gas. At neutral or acid pH, the reaction is slow, but is catalyzed by the carbonic anhydrase. Solutions containing the hydroxide ion attack glass, in this case, the silicates in glass are acting as acids
27.
Alkoxide
–
An alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They can be written as RO−, where R is the organic substituent, alkoxides are strong bases and, when R is not bulky, good nucleophiles and good ligands. Alkoxides, although generally not stable in protic solvents such as water, occur widely as intermediates in various reactions, transition metal alkoxides are widely used for coatings and as catalysts. Enolates are unsaturated alkoxides derived by deprotonation of a C-H bond adjacent to a ketone or aldehyde, the nucleophilic center for simple alkoxides is located on the oxygen, whereas the nucleophilic site on enolates is delocalized onto both carbon and oxygen sites. Phenoxides are close relatives of the alkoxides, in which the group is replaced by a derivative of benzene. Phenol is more acidic than a typical alcohol, thus, phenoxides are correspondingly less basic and they are, however, often easier to handle, and yield derivatives that are more crystalline than those of the alkoxides. Alkoxides can be produced by several routes starting from an alcohol, highly reducing metals react directly with alcohols to give the corresponding metal alkoxide. The alcohol serves as an acid, and hydrogen is produced as a by-product, many other metal and main group halides can be used instead of titanium, for example SiCl4, ZrCl4, and PCl3. Many alkoxides can be prepared by dissolution of the corresponding metals in water-free alcohols in the presence of electroconductive additive. The metals may be Co, Ga, Ge, Hf, Fe, Ni, Nb, Mo, La, Re, Sc, Si, Ti, Ta, W, Y, Zr, etc. The conductive additive may be lithium chloride, quaternary ammonium halide, some examples of metal alkoxides obtained by this technique, Ti4, Nb210, Ta210,2, Re2O36, Re4O612, and Re4O610. Other alcohols can be employed in place of water, in this way one alkoxide can be converted to another, and the process is properly referred to as alcoholysis. The position of the equilibrium can be controlled by the acidity of the alcohol, for example phenols typically react with alkoxides to release alcohols, more simply, the alcoholysis can be controlled by selectively evaporating the more volatile component. In this way, ethoxides can be converted to butoxides, since ethanol is more volatile than butanol, in the transesterification process, metal alkoxides react with esters to bring about an exchange of alkyl groups between metal alkoxide and ester. Sodium methoxide, for example, is used for this purpose. Many metal alkoxide compounds also feature oxo-ligands, oxo-ligands typically arise via the hydrolysis, often accidentally, and via ether elimination,2 LnMOR → 2O + R2O Additionally, low valent metal alkoxides are susceptible to oxidation by air. Characteristically, transition metal alkoxides are polynuclear, that is they contain more than one metal, alkoxides are sterically undemanding and highly basic ligands that tend to bridge metals. Upon the isomorphic substitution of metal atoms close in properties crystalline complexes of variable composition are formed, the metal ratio in such compounds can vary over a broad range
28.
Metal amides
–
Metal amides are a class of coordination compounds composed of a metal center with amide ligands of the form NR2. Amide ligands have two electron pairs available for bonding, in principle, they can be terminal or bridging. In these two examples, the ligands are both bridging and terminal, In practice, bulky amide ligands have a lesser tendency to bridge. Amide ligands may participate in metal-ligand π-bonding giving a complex with the center being co-planar with the nitrogen. Metal bisamides form a significant subcategory of metal amide compounds and these compounds tend to be discrete and soluble in organic solvents. Lithium amides are the most important amides, as they are prepared from n-butyllithium and the appropriate amine. Potassium amides are prepared by transmetallation of lithium amides with potassium t-butoxide or by reaction of the amine with potassium, potassium hydride, n-butylpotassium, the alkali metal amides, MNH2 are commercially available. Sodium amide is synthesized from sodium metal and ammonia with ferric nitrate catalyst, the sodium compound is white, but the presence of metallic iron turns the commercial material gray. 2 Na +2 NH3 →2 NaNH2 + H2 Lithium diisopropylamide is a popular non-nucleophilic base used in organic synthesis, unlike many other bases, the steric bulk prevents this base from acting as a nucleophile. It is commercially available, usually as a solution in hexane and it may be readily prepared from n-butyllithium and diisopropylamine
29.
Nucleophilic aromatic substitution
–
A nucleophilic aromatic substitution is a substitution reaction in organic chemistry in which the nucleophile displaces a good leaving group, such as a halide, on an aromatic ring. Aryl halides cannot undergo SN2 reaction. The C–Br bond is in the plane of the ring as the atom is trigonal. To attack from the back, the nucleophile would have to appear inside the benzene ring, SN1 reaction is possible but very unfavourable. It would involve the loss of the leaving group and the formation of an aryl cation. The following is the mechanism of a nucleophilic aromatic substitution of 2. In this sequence the carbons are numbered clockwise from 1–6 starting with the 1 carbon at 12 oclock, since the nitro group is an activator toward nucleophilic substitution, and a meta director, it allows the benzene carbon to which it is bonded to have a negative charge. In the Meisenheimer complex, the electrons of the carbanion become bonded to the aromatic pi system which allows the ipso carbon to temporarily bond with the hydroxyl group. In order to return to an energy state, either the hydroxyl group leaves. A small percentage of the intermediate loses the chloride to become the product, since 2, 4-dinitrophenol is in a lower energy state it will not return to form the reactant, so after some time has passed, the reaction reaches chemical equilibrium that favors the 2, 4-dinitrophenol. The formation of the resonance-stabilized Meisenheimer complex is slow because it is in an energy state than the aromatic reactant. The loss of the chloride is fast, because the ring becomes aromatic again, some typical substitution reactions on arenes are listed below. In the Bamberger rearrangement N-phenylhydroxylamines rearrange to 4-aminophenols, in the Sandmeyer reaction and the Gattermann reaction diazonium salts react with halides. The Smiles rearrangement is the version of this reaction type. Nucleophilic aromatic substitution is not limited to arenes, however, the takes place even more readily with heteroarenes. Pyridines are especially reactive when substituted in the ortho position or aromatic para position because then the negative charge is effectively delocalized at the nitrogen position. One classic reaction is the Chichibabin reaction in which pyridine is reacted with an alkali-metal amide such as sodium amide to form 2-aminopyridine, in the compound methyl 3-nitropyridine-4-carboxylate, the meta nitro group is actually displaced by fluorine with caesium fluoride in DMSO at 120°C. With carbon nucleophiles such as 1, 3-dicarbonyl compounds the reaction has been demonstrated as a method for the synthesis of chiral molecules. First reported in 2005, the organocatalyst is derived from cinchonidine, electrophilic aromatic substitution Nucleophile Substitution reaction SN1 reaction SN2 reaction SNi reaction Nucleophilic aliphatic substitution Nucleophilic acyl substitution
30.
Meisenheimer complex
–
A Meisenheimer complex or Jackson–Meisenheimer complex in organic chemistry is a 1,1 reaction adduct between an arene carrying electron withdrawing groups and nucleophile. These complexes are found as intermediates in nucleophilic aromatic substitution but stable. The early development of type of complex takes place around the turn of the 19th century. In 1886 Janovski observed an intense color when he mixed meta-dinitrobenzene with an alcoholic solution of alkali. In 1895 Lobry de Bruyn investigated a red substance formed in the reaction of trinitrobenzene with potassium hydroxide in methanol, in 1900 Jackson and Gazzolo reacted trinitroanisole with sodium methoxide and proposed a quinoid structure for the reaction product. In 1902 Jakob Meisenheimer observed that by acidifying their reaction product, with three electron withdrawing groups, the negative charge in the complex is located at one of the nitro groups according to the quinoid model. When less electron poor arenes this charge is delocalized over the entire ring, in one study a Meisenheimer arene was allowed to react with a strongly electron-releasing arene forming a zwitterionic Meisenheimer–Wheland complex. The Wheland intermediate is its number and the reactive intermediate in electrophilic aromatic substitution. The structure of this complex was confirmed by NMR spectroscopy, the Janovski reaction is the reaction of 1, 3-dinitrobenzene with an enolizable ketone to the Meisenheimer adduct. In the Zimmermann reaction the Janovski adduct is oxidized with excess base to a strongly colored enolate with subsequent reduction of the compound to the aromatic nitro amine. This reaction is the basis of the Zimmermann test used for the detection of ketosteroids, the Jackson-Meisenheimer Complex was named after the American Organic Chemist, Charles Loring Jackson and the German Organic Chemist, Jakob Meisenheimer. The Janovski Reaction was named for the Czech Chemist, Jaroslav Janovski, the Zimmermann Reaction was named after the German Chemist, Wilhelm Zimmermann. Lastly, the Wheland Intermediate was named for the American Chemist, George Willard Wheland
31.
Lewis acids and bases
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A Lewis acid is a chemical species that reacts with a Lewis base to form a Lewis adduct. A Lewis base, then, is any species that donates a pair of electrons to a Lewis acid to form a Lewis adduct, for example, OH− and NH3 are Lewis bases, because they can donate a lone pair of electrons. In the adduct, the Lewis acid and base share an electron pair furnished by the Lewis base, usually the terms Lewis acid and Lewis base are defined within the context of a specific chemical reaction. For example, in the reaction of Me3B and NH3 to give Me3BNH3, Me3B acts as a Lewis acid, the terminology refers to the contributions of Gilbert N. Lewis. Another example is boron trifluoride etherate, BF3•Et2O, the center dot is also used to represent hydrate coordination in various crystals, as in MgSO4•7H2O for hydrated magnesium sulfate. In general, however, the bond is viewed as simply somewhere along a continuum between idealized covalent bonding and ionic bonding. Classically, the term Lewis acid is restricted to trigonal planar species with an empty p orbital, for the purposes of discussion, even complex compounds such as Et3Al2Cl3 and AlCl3 are treated as trigonal planar Lewis acids. Other reactions might simply be referred to as acid-catalyzed reactions, some compounds, such as H2O, are both Lewis acids and Lewis bases, because they can either accept a pair of electrons or donate a pair of electrons, depending upon the reaction. Simplest are those that react directly with the Lewis base, but more common are those that undergo a reaction prior to forming the adduct. Again, the description of a Lewis acid is used loosely. For example, in solution, bare protons do not exist, BF3 + OMe2 → BF3OMe2 Both BF4− and BF3OMe2 are Lewis base adducts of boron trifluoride. Well known cases are the aluminium trihalides, which are viewed as Lewis acids. Aluminium trihalides, unlike the boron trihalides, do not exist in the form AlX3, a simpler case is the formation of adducts of borane. Monomeric BH3 does not exist appreciably, so the adducts of borane are generated by degradation of diborane, B2H6 +2 H− →2 BH4− In this case, an intermediate B2H7− can be isolated. Many metal complexes serve as Lewis acids, but usually only after dissociating a more weakly bound Lewis base, 2+ +6 NH3 → 2+ +6 H2O The proton is one of the strongest but is also one of the most complicated Lewis acids. It is convention to ignore the fact that a proton is heavily solvated, the key step is the acceptance by AlCl3 of a chloride ion lone-pair, forming AlCl4− and creating the strongly acidic, that is, electrophilic, carbonium ion. RCl +AlCl3 → R+ + AlCl4− A Lewis base is an atomic or molecular species where the highest occupied molecular orbital is highly localized, typical Lewis bases are conventional amines such as ammonia and alkyl amines. Other common Lewis bases include pyridine and its derivatives, some of the main classes of Lewis bases are amines of the formula NH3−xRx where R = alkyl or aryl
32.
Thiol
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In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl or sulphydryl group. Thiols are the analogue of alcohols, and the word is a portmanteau of thion + alcohol. The –SH functional group itself is referred to as either a group or a sulfhydryl group. Many thiols have strong odors resembling that of garlic or rotten eggs, thiols are used as odorants to assist in the detection of natural gas, and the smell of natural gas is due to the smell of the thiol used as the odorant. Thiols are sometimes referred to as mercaptans, thiols and alcohols have similar connectivity. Because sulfur is a larger element than oxygen, the C–S bond lengths, the C–S–H angles approach 90° whereas the angle for the C-O-H group are more open. In the solid or liquids, the hydrogen-bonding between individual groups is weak, the main cohesive force being van der Waals interactions between the highly polarizable divalent sulfur centers. Due to the lesser electronegativity difference between sulfur and hydrogen compared to oxygen and hydrogen, an S–H bond is less polar than the hydroxyl group, thiols have a lower dipole moment relative to the corresponding alcohol. There are several ways to name the alkylthiols, The suffix -thiol is added to the name of the alkane and this method is nearly identical to naming an alcohol and is used by the IUPAC. The word mercaptan replaces alcohol in the name of the equivalent alcohol compound, example, CH3SH would be methyl mercaptan, just as CH3OH is called methyl alcohol. The term sulfanyl or mercapto is used as a prefix, many thiols have strong odors resembling that of garlic. The odors of thiols, particularly those of low weight, are often strong. The spray of skunks consists mainly of low-molecular-weight thiols and derivatives and these compounds are detectable by the human nose at concentrations of only 10 parts per billion. Human sweat contains /-3-methyl-3-sulfanylhexan-1-ol, detectable at 2 parts per billion and having a fruity, methanethiol is a strong-smelling volatile thiol, also detectable at parts per billion levels, found in male mouse urine. Lawrence C. Katz and co-workers showed that MTMT functioned as a semiochemical, activating certain mouse olfactory sensory neurons, attracting female mice. Copper has been shown to be required by a specific mouse olfactory receptor, MOR244-3, thiols are also responsible for a class of wine faults caused by an unintended reaction between sulfur and yeast and the skunky odor of beer that has been exposed to ultraviolet light. Not all thiols have unpleasant odors, for example, furan-2-ylmethanethiol contributes to the aroma of roasted coffee, whereas grapefruit mercaptan, a monoterpenoid thiol, is responsible for the characteristic scent of grapefruit. The effect of the compound is present only at low concentrations
33.
Elimination reaction
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An elimination reaction is a type of organic reaction in which two substituents are removed from a molecule in either a one or two-step mechanism. The one-step mechanism is known as the E2 reaction, and the mechanism is known as the E1 reaction. The numbers do not have to do with the number of steps in the mechanism, in rare cases, for molecules possessing particularly poor leaving groups, a third type of reaction, E1CB, exists. In most organic elimination reactions, at least one hydrogen is lost to form the double bond and it is also possible that a molecule undergoes reductive elimination, by which the valence of an atom in the molecule decreases by two, though this is more common in inorganic chemistry. An important class of reactions is those involving alkyl halides, with good leaving groups. Elimination may be considered the reverse of an addition reaction, when the substrate is asymmetric, regioselectivity is determined by Zaitsevs rule or through Hofmann elimination if the carbon with the most substituted hydrogen is inaccessible. During the 1920s, Sir Christopher Ingold proposed a model to explain a peculiar type of chemical reaction, the reaction involves a one-step mechanism in which carbon-hydrogen and carbon-halogen bonds break to form a double bond. The specifics of the reaction are as follows, E2 is a single step elimination and it is typically undergone by primary substituted alkyl halides, but is possible with some secondary alkyl halides and other compounds. The reaction rate is second order, because its influenced by both the alkyl halide and the base, because the E2 mechanism results in the formation of a pi bond, the two leaving groups need to be antiperiplanar. An antiperiplanar transition state has staggered conformation with lower energy than a transition state which is in eclipsed conformation with higher energy. The reaction mechanism involving staggered conformation is more favorable for E2 reactions, E2 typically uses a strong base. It must be enough to remove a weakly acidic hydrogen. In order for the pi bond to be created, the hybridization of carbons needs to be lowered from sp3 to sp2, the C-H bond is weakened in the rate determining step and therefore a primary deuterium isotope effect much larger than 1 is observed. E2 competes with the SN2 reaction mechanism if the base can also act as a nucleophile, an example of this type of reaction in scheme 1 is the reaction of isobutylbromide with potassium ethoxide in ethanol. The reaction products are isobutylene, ethanol and potassium bromide, E1 is a model to explain a particular type of chemical elimination reaction. E1 stands for unimolecular elimination and has the following specificities and it is a two-step process of elimination, ionization and deprotonation. Ionization, the carbon-halogen bond breaks to give a carbocation intermediate, E1 typically takes place with tertiary alkyl halides, but is possible with some secondary alkyl halides. The reaction rate is influenced only by the concentration of the alkyl halide because carbocation formation is the slowest step, the reaction usually occurs in the complete absence of a base or the presence of only a weak base
34.
Substitution reaction
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Substitution reaction is a chemical reaction during which one functional group in a chemical compound is replaced by another functional group. Substitution reactions are of importance in organic chemistry. Substitution reactions in chemistry are classified either as electrophilic or nucleophilic depending upon the reagent involved. There are other classifications as well that are mentioned below, detailed understanding of a reaction type helps to predict the product outcome in a reaction. It also is helpful for optimizing a reaction with regard to such as temperature. A good example of a reaction is halogenation. When chlorine gas is irradiated, some of the molecules are split into two chlorine radicals whose free electrons are strongly nucleophilic, one of them breaks a weak C-H covalent bond and grabs the liberated proton to form the electrically neutral H-Cl. The other radical reforms a covalent bond with the CH3. to form CH3Cl, as it does so, it replaces a weaker nucleophile which then becomes a leaving group, The remaining positive or partially positive atom becomes an electrophile. The whole molecular entity of which the electrophile and the group are part is usually called the substrate. The most general form for the reaction may be given as where R-LG indicates the substrate, nuc, + R-LG → R-Nuc + LG, The electron pair from the nucleophile attacks the substrate forming a new covalent bond Nuc-R-LG. The prior state of charge is restored when the group departs with an electron pair. The principal product in case is R-Nuc. In such reactions, the nucleophile is usually neutral or negatively charged. An example of substitution is the hydrolysis of an alkyl bromide, R-Br, under basic conditions, where the attacking nucleophile is the base OH−. These substitutions can be produced by two different mechanisms categorized at, unimolecular nucleophilic substitution and bimolecular nucleophilic substitution, the SN1 mechanism has two steps. In the first step, the group departs, forming a carbocation C+. In the second step, the nucleophilic reagent attaches to the carbocation, if the substrate has a chiral carbon, this mechanism can result in either inversion of the stereochemistry or retention of configuration. For an example with diagrams see the reaction of tert-butyl bromide with water shown at SN1 reaction, the SN2 mechanism have just one step
35.
Carbocation
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A carbocation is an ion with a positively charged carbon atom. Among the simplest examples are methenium CH+3, methanium CH+5, some carbocations may have two or more positive charges, on the same carbon atom or on different atoms, such as the ethylene dication C 2H2+4. Until the early 1970s, all carbocations were called carbonium ions and this nomenclature was proposed by G. A. Olah. One textbook retains the name of carbonium ion for carbenium ion to this day. The history of carbocations dates back to 1891 when G. Merling reported that he added bromine to tropylidene and then heated the product to obtain a crystalline, water-soluble material, C 7H 7Br. He did not suggest a structure for it, however, Doering and this ion is predicted to be aromatic by Hückels rule. In 1902, Norris and Kehrman independently discovered that colorless triphenylmethanol gives deep-yellow solutions in concentrated sulfuric acid, triphenylmethyl chloride similarly formed orange complexes with aluminium and tin chlorides. In 1902, Adolf von Baeyer recognized the character of the compounds formed. He dubbed the relationship between color and salt formation halochromy, of which green is a prime example. Carbocations are reactive intermediates in organic reactions. This idea, first proposed by Julius Stieglitz in 1899, was developed by Hans Meerwein in his 1922 study of the Wagner–Meerwein rearrangement. Carbocations were also found to be involved in the SN1 reaction, the E1 reaction, the chemical establishment was reluctant to accept the notion of a carbocation and for a long time the Journal of the American Chemical Society refused articles that mentioned them. The first NMR spectrum of a carbocation in solution was published by Doering et al. in 1958. It was the ion, made by treating hexamethylbenzene with methyl chloride. The stable 7-norbornadienyl cation was prepared by Story et al. in 1960 by reacting norbornadienyl chloride with silver tetrafluoroborate in sulfur dioxide at −80 °C, the NMR spectrum established that it was non-classically bridged. In 1962, Olah directly observed the tert-butyl carbocation by nuclear magnetic resonance as a species on dissolving tert-butyl fluoride in magic acid. The NMR of the norbornyl cation was first reported by Schleyer et al. the charged carbon atom in a carbocation is a sextet, i. e. it has only six electrons in its outer valence shell instead of the eight valence electrons that ensures maximum stability. Therefore, carbocations are often reactive, seeking to fill the octet of electrons as well as regain a neutral charge
36.
Acyl group
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An acyl group is a moiety derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids. It contains a double bonded oxygen atom and an alkyl group, in organic chemistry, the acyl group is usually derived from a carboxylic acid. Therefore, it has the formula RCO–, where R represents a group that is linked to the carbon atom of the group by a single bond. Although the term is almost always applied to compounds, acyl groups can in principle be derived from other types of acids such as sulfonic acids. In the most common arrangement, acyl groups are attached to a molecular fragment, in which case the carbon. Well-known acyl compounds are the acyl chlorides, such as acetyl chloride and these compounds, which are treated as sources of acylium cations, are good reagents for attaching acyl groups to various substrates. Amides and esters are classes of compounds, as are ketones and aldehydes. Acylium ions are cations of the formula RCO+, such species are common reactive intermediates, for example, in the Friedel–Crafts acylations also in many other organic reactions such as the Hayashi rearrangement. Acylium cations are characteristic fragments observed in EI-mass spectra of ketones, acyl radicals are readily generated from aldehydes by H-atom abstraction. However, they undergo rapid decarbonylation to afford the alkyl radical, acyl anions are almost always unstable, usually too unstable to be exploited synthetically. Hence synthetic chemists have developed various acyl anion equivalents as surrogates, in biochemistry there are many instances of acyl groups, in all major categories of biochemical molecules. Acyl-CoAs are acyl derivatives formed via fatty acid metabolism, acetyl-CoA, the most common derivative, serves as an acyl donor in many biosynthetic transformations. Names of acyl groups of amino acids are formed by the replacement of the ending -ine by the ending -yl, for example, the acyl group of glycine is glycyl, and of lysine is lysyl. Names of acyl groups of ribonucleoside monophosphates such as AMP, GMP, CMP, and UMP are adenylyl, guanylyl, cytidylyl, in phospholipids, the acyl group of phosphatidic acid is called phosphatidyl-. Acyl ligands are intermediates in many reactions, which are important in some catalytic reactions. Metal acyls arise usually via insertion of carbon monoxide into metal–alkyl bonds, metal acyls also arise from reactions involving acyl chlorides with low-valence metal complexes or by the reaction of organolithium compounds with metal carbonyls. Metal acyls are often described by two structures, one of which emphasizes the basicity of the oxygen center. O-alkylation of metal acyls gives Fischer carbene complexes, the names of acyl groups are derived typically from the corresponding acid by substituting the acid ending -ic with the ending -yl as shown in the table below
37.
Enol
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The terms enol and alkenol are portmanteaus deriving from -ene/alkene and the -ol suffix indicating the hydroxyl group of alcohols, dropping the terminal -e of the first term. Generation of enols often involves removal of an adjacent to the carbonyl group—i. e. Deprotonation, its removal as a proton, H+, when this proton is not returned at the end of the stepwise process, the result is an anion termed an enolate. The enolate structures shown are schematic, a modern representation considers the molecular orbitals that are formed and occupied by electrons in the enolate. Similarly, generation of the enol often is accompanied by trapping or masking of the group as an ether. The importance of enols in accomplishing nature and humankinds chemical transformations makes them irreplaceable, moreover, the substituents and conditions determine the preponderant conformations of these reactive species, and therefore dictate the stereochemical outcomes of their reactions. As indicated in the image above, carbonyl compounds that have an α-hydrogen atom adjacent to a carbonyl group—like organic esters, ketones. The examples of the 3-pentanone and 2, 4-pentanedione tautomerization equilibrium appear in the gallery of images above, in the case of ketones, it is formally called a keto-enol tautomerism, though this name is often more generally applied to all such tautomerizations. In organic compounds with two carbonyls, the constitutional isomer may be stabilized. Hence, while one α-hydrogen is required, the substituent in the α-position may be variable. Enol stabilization is due in part to the intramolecular hydrogen bonding that is available to it, as shown for the 2. In the case of malonaldehyde, over 99 mole% of the compound is in the enol form. While lower for 3-ketoaldehydes and 1, 3-diketones, the form still predominates, e. g. in the case of 2, 4-pentanedione. When keto-enol tautomerism occurs the keto or enol is deprotonated and an anion, enolates can exist in quantitative amounts in strictly Brønsted acid free conditions, since they are generally very basic. In enolates the anionic charge is delocalized over the oxygen and the carbon, enolate forms can be stabilized by this delocalization of the charge over three atoms. In valence bond theory, the structure and stability is explained by a phenomenon known as resonance. The two resonance structures shown here constitute the resonance hybrid, in molecular orbital theory, it is represented by three delocalized molecular orbitals, two of them filled. In ketones with α-hydrogens on both sides of the carbon, selectivity of deprotonation may be achieved to generate two different enolate structures
38.
Copper
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Copper is a chemical element with symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with high thermal and electrical conductivity. A freshly exposed surface of copper has a reddish-orange color. Copper is one of the few metals that occur in nature in directly usable metallic form as opposed to needing extraction from an ore and this led to very early human use, from c.8000 BC. Copper used in buildings, usually for roofing, oxidizes to form a green verdigris, Copper is sometimes used in decorative art, both in its elemental metal form and in compounds as pigments. Copper compounds are used as agents, fungicides, and wood preservatives. Copper is essential to all living organisms as a trace dietary mineral because it is a key constituent of the enzyme complex cytochrome c oxidase. In molluscs and crustaceans, copper is a constituent of the blood pigment hemocyanin, replaced by the hemoglobin in fish. In humans, copper is found mainly in the liver, muscle, the adult body contains between 1.4 and 2.1 mg of copper per kilogram of body weight. The filled d-shells in these elements contribute little to interatomic interactions, unlike metals with incomplete d-shells, metallic bonds in copper are lacking a covalent character and are relatively weak. This observation explains the low hardness and high ductility of single crystals of copper, at the macroscopic scale, introduction of extended defects to the crystal lattice, such as grain boundaries, hinders flow of the material under applied stress, thereby increasing its hardness. For this reason, copper is supplied in a fine-grained polycrystalline form. The softness of copper partly explains its high conductivity and high thermal conductivity. The maximum permissible current density of copper in open air is approximately 3. 1×106 A/m2 of cross-sectional area, Copper is one of a few metallic elements with a natural color other than gray or silver. Pure copper is orange-red and acquires a reddish tarnish when exposed to air, as with other metals, if copper is put in contact with another metal, galvanic corrosion will occur. A green layer of verdigris can often be seen on old structures, such as the roofing of many older buildings. Copper tarnishes when exposed to sulfur compounds, with which it reacts to form various copper sulfides. There are 29 isotopes of copper, 63Cu and 65Cu are stable, with 63Cu comprising approximately 69% of naturally occurring copper, both have a spin of 3⁄2
39.
Methyl trifluoromethanesulfonate
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Methyl trifluoromethanesulfonate, also commonly called methyl triflate, is the organic compound with the formula CF3SO2OCH3. It is a liquid which finds use in organic chemistry as a very powerful methylating agent. Methyl triflate is commercially available, however it may also be prepared in the laboratory via a number of routes, for instance, the reaction of methanol with trifluoromethanesulfonic anhydride in the presence of pyridine. In this approach the methyl triflate may be removed from the triflic acid by-product by fractional distillation, alternatively, triflic acid can be methylated by high temperature reactions with other alkylating agents, such as methyl iodide or dimethyl carbonate. These compounds alkylate faster and with wider range of substrates than traditional methylating agents such as methyl iodide, one ranking of alkylating agents is 3O+ > CF3SO2OCH3 ≈ FSO2OCH3 > 2SO4 > CH3I. It will alkylate many functional groups that are weakly basic such as aldehydes, amides. It does not methylate benzene or the bulky 2, 6-di-tert-butylpyridine and its ability to methylate N-heterocycles is exploited in certain deprotection schemes
