1.
Pyridine
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Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one methine group replaced by a nitrogen atom, the pyridine ring occurs in many important compounds, including azines and the vitamins niacin and pyridoxine. Pyridine was discovered in 1849 by the Scottish chemist Thomas Anderson as one of the constituents of bone oil, two years later, Anderson isolated pure pyridine through fractional distillation of the oil. It is a colorless, highly flammable, weakly alkaline, water-soluble liquid with a distinctive, pyridine is used as a precursor to agrochemicals and pharmaceuticals and is also an important solvent and reagent. Pyridine is added to ethanol to make it unsuitable for drinking and it is used in the in vitro synthesis of DNA, in the synthesis of sulfapyridine, antihistaminic drugs tripelennamine and mepyramine, as well as water repellents, bactericides, and herbicides. Some chemical compounds, although not synthesized from pyridine, contain its ring structure and they include B vitamins niacin and pyridoxal, the anti-tuberculosis drug isoniazid, nicotine and other nitrogen-containing plant products. Historically, pyridine was produced from tar and as a byproduct of coal gasification. Pyridine is a liquid that boils at 115.2 °C. Its density,0.9819 g/cm3, is close to that of water, and its index is 1.5093 at a wavelength of 589 nm. Addition of up to 40 mol% of water to pyridine gradually lowers its melting point from −41.6 °C to −65.0 °C, the molecular electric dipole moment is 2.2 debyes. Pyridine is diamagnetic and has a susceptibility of −48.7 × 10−6 cm3·mol−1. The standard enthalpy of formation is 100.2 kJ·mol−1 in the phase and 140.4 kJ·mol−1 in the gas phase. At 25 °C pyridine has a viscosity of 0.88 mPa/s, the enthalpy of vaporization is 35.09 kJ·mol−1 at the boiling point and normal pressure. The enthalpy of fusion is 8.28 kJ·mol−1 at the melting point, pyridine crystallizes in an orthorhombic crystal system with space group Pna21 and lattice parameters a =1752 pm, b =897 pm, c =1135 pm, and 16 formula units per unit cell. For comparison, crystalline benzene is also orthorhombic, with space group Pbca, a =729.2 pm, b =947.1 pm, c =674.2 pm and this difference is partly related to the lower symmetry of the individual pyridine molecule. A trihydrate is known, it crystallizes in an orthorhombic system in the space group Pbca, lattice parameters a =1244 pm, b =1783 pm, c =679 pm. The critical parameters of pyridine are pressure 6.70 MPa, temperature 620 K, the optical absorption spectrum of pyridine in hexane contains three bands at the wavelengths of 195 nm,251 nm and 270 nm. The 1H nuclear magnetic resonance spectrum of pyridine contains three signals with the intensity ratio of 2,1,2 that correspond to the three chemically different protons in the molecule
2.
Allotropes of sulfur
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The allotropes of sulfur refers to the many allotropes of the element sulfur. In terms of number of allotropes, sulfur is second only to carbon. In addition to the allotropes, each allotrope often exists in polymorphs, furthermore, because elemental sulfur has been an item of commerce for centuries, its various forms are given traditional names. Early workers identified some forms that have proved to be single or mixtures of allotropes. Some forms have been named for their appearance, e. g. mother of pearl sulfur, or alternatively named for a chemist who was pre-eminent in identifying them, e. g. Muthmanns sulfur I or Engels sulfur. The most commonly encountered form of sulfur is the polymorph of S8. Two other polymorphs are known, also nearly identical molecular structures. In addition to S8, sulfur rings of 6,7, at least five allotropes are uniquely formed at high pressures, two of which are metallic. The number of sulfur allotropes reflects the relatively strong S−S bond of 265 kJ/mol, furthermore, unlike most elements, the allotropes of sulfur can be manipulated in solutions of organic solvents and is amenable to analysis by HPLC. The pressure-temperature phase diagram for sulfur is complex, the region labeled I, is α-sulfur. See the legend for further identifications and information, and see the section on high pressure forms for information on these phases. In a high-pressure study at ambient temperatures, four new forms, termed II, III, IV, V have been characterized. Solid forms II and III are polymeric, while IV and V are metallic, laser irradiation of solid samples produces three sulfur forms below 200–300 kbar. Two methods exist for the preparation of the cyclo-sulfur allotropes and this was first prepared by M. R. Engel in 1891 by reacting HCl with thiosulfate, HS2O3−. Cyclo-S6 is orange-red and forms a rhombohedral crystal and it is called ρ-sulfur, ε-sulfur, Engels sulfur and Atens sulfur. All of the atoms are equivalent. It is a yellow solid. Four forms of cyclo-heptasulfur are known, the cyclo-S7 ring has an unusual range of bond lengths of 199. 3–218.1 pm
3.
Cyclic compound
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A cyclic compound is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. Rings may vary in size from three to many atoms, and include examples where all the atoms are carbon, none of the atoms are carbon, cyclic compound examples, All-carbon and more complex natural cyclic compounds. Indeed, the development of important chemical concept arose, historically. A cyclic compound or ring compound is a compound at least some of whose atoms are connected to form a ring, rings vary in size from 3 to many tens or even hundreds of atoms. Examples of ring compounds readily include cases where, all the atoms are carbon, none of the atoms are carbon, common atoms can form varying numbers of bonds, and many common atoms readily form rings. As a consequence of the variability that is thermodynamically possible in cyclic structures. IUPAC nomenclature has extensive rules to cover the naming of cyclic structures, the term macrocycle is used when a ring-containing compound has a ring of 8 or more atoms. The term polycyclic is used more than one ring appears in a single molecule. Naphthalene is formally a polycyclic, but is specifically named as a bicyclic compound. Several examples of macrocyclic and polycyclic structures are given in the gallery below. The atoms that are part of the structure are called annular atoms. The vast majority of compounds are organic, and of these. Inorganic atoms form cyclic compounds as well, examples include sulfur, silicon, phosphorus, and boron. Hantzsch–Widman nomenclature is recommended by the IUPAC for naming heterocycles, cyclic compounds may or may not exhibit aromaticity, benzene is an example of an aromatic cyclic compound, while cyclohexane is non-aromatic. As a result of their stability, it is difficult to cause aromatic molecules to break apart. Organic compounds that are not aromatic are classified as aliphatic compounds—they might be cyclic, nevertheless, many non-benzene aromatic compounds exist. In living organisms, for example, the most common aromatic rings are the bases in RNA and DNA. A functional group or other substituent that is aromatic is called an aryl group, the earliest use of the term “aromatic” was in an article by August Wilhelm Hofmann in 1855
4.
Chemical element
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A chemical element or element is a species of atoms having the same number of protons in their atomic nuclei. There are 118 elements that have identified, of which the first 94 occur naturally on Earth with the remaining 24 being synthetic elements. There are 80 elements that have at least one stable isotope and 38 that have exclusively radioactive isotopes, iron is the most abundant element making up Earth, while oxygen is the most common element in the Earths crust. Chemical elements constitute all of the matter of the universe. The two lightest elements, hydrogen and helium, were formed in the Big Bang and are the most common elements in the universe. The next three elements were formed mostly by cosmic ray spallation, and are rarer than those that follow. Formation of elements with from 6 to 26 protons occurred and continues to occur in main sequence stars via stellar nucleosynthesis, the high abundance of oxygen, silicon, and iron on Earth reflects their common production in such stars. The term element is used for atoms with a number of protons as well as for a pure chemical substance consisting of a single element. A single element can form multiple substances differing in their structure, when different elements are chemically combined, with the atoms held together by chemical bonds, they form chemical compounds. Only a minority of elements are found uncombined as relatively pure minerals, among the more common of such native elements are copper, silver, gold, carbon, and sulfur. All but a few of the most inert elements, such as gases and noble metals, are usually found on Earth in chemically combined form. While about 32 of the elements occur on Earth in native uncombined forms. For example, atmospheric air is primarily a mixture of nitrogen, oxygen, and argon, the history of the discovery and use of the elements began with primitive human societies that found native elements like carbon, sulfur, copper and gold. Later civilizations extracted elemental copper, tin, lead and iron from their ores by smelting, using charcoal, alchemists and chemists subsequently identified many more, almost all of the naturally occurring elements were known by 1900. Save for unstable radioactive elements with short half-lives, all of the elements are available industrially, almost all other elements found in nature were made by various natural methods of nucleosynthesis. On Earth, small amounts of new atoms are produced in nucleogenic reactions, or in cosmogenic processes. Of the 94 naturally occurring elements, those with atomic numbers 1 through 82 each have at least one stable isotope, Isotopes considered stable are those for which no radioactive decay has yet been observed. Elements with atomic numbers 83 through 94 are unstable to the point that radioactive decay of all isotopes can be detected, the very heaviest elements undergo radioactive decay with half-lives so short that they are not found in nature and must be synthesized
5.
Organic chemistry
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Study of structure includes many physical and chemical methods to determine the chemical composition and the chemical constitution of organic compounds and materials. In the modern era, the range extends further into the table, with main group elements, including, Group 1 and 2 organometallic compounds. They either form the basis of, or are important constituents of, many products including pharmaceuticals, petrochemicals and products made from them, plastics, fuels and explosives. Before the nineteenth century, chemists generally believed that compounds obtained from living organisms were endowed with a force that distinguished them from inorganic compounds. According to the concept of vitalism, organic matter was endowed with a vital force, during the first half of the nineteenth century, some of the first systematic studies of organic compounds were reported. Around 1816 Michel Chevreul started a study of soaps made from various fats and he separated the different acids that, in combination with the alkali, produced the soap. Since these were all compounds, he demonstrated that it was possible to make a chemical change in various fats, producing new compounds. In 1828 Friedrich Wöhler produced the chemical urea, a constituent of urine, from inorganic starting materials. The event is now accepted as indeed disproving the doctrine of vitalism. In 1856 William Henry Perkin, while trying to manufacture quinine accidentally produced the organic dye now known as Perkins mauve and his discovery, made widely known through its financial success, greatly increased interest in organic chemistry. A crucial breakthrough for organic chemistry was the concept of chemical structure, ehrlich popularized the concepts of magic bullet drugs and of systematically improving drug therapies. His laboratory made decisive contributions to developing antiserum for diphtheria and standardizing therapeutic serums, early examples of organic reactions and applications were often found because of a combination of luck and preparation for unexpected observations. The latter half of the 19th century however witnessed systematic studies of organic compounds, the development of synthetic indigo is illustrative. The production of indigo from plant sources dropped from 19,000 tons in 1897 to 1,000 tons by 1914 thanks to the methods developed by Adolf von Baeyer. In 2002,17,000 tons of indigo were produced from petrochemicals. In the early part of the 20th Century, polymers and enzymes were shown to be large organic molecules, the multiple-step synthesis of complex organic compounds is called total synthesis. Total synthesis of natural compounds increased in complexity to glucose. For example, cholesterol-related compounds have opened ways to synthesize complex human hormones, since the start of the 20th century, complexity of total syntheses has been increased to include molecules of high complexity such as lysergic acid and vitamin B12
6.
International Union of Pure and Applied Chemistry
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The International Union of Pure and Applied Chemistry /ˈaɪjuːpæk/ or /ˈjuːpæk/ is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Council for Science, IUPAC is registered in Zürich, Switzerland, and the administrative office, known as the IUPAC Secretariat, is in Research Triangle Park, North Carolina, United States. This administrative office is headed by IUPACs executive director, currently Lynn Soby, IUPAC was established in 1919 as the successor of the International Congress of Applied Chemistry for the advancement of chemistry. Its members, the National Adhering Organizations, can be national chemistry societies, national academies of sciences, there are fifty-four National Adhering Organizations and three Associate National Adhering Organizations. IUPACs Inter-divisional Committee on Nomenclature and Symbols is the world authority in developing standards for the naming of the chemical elements. Since its creation, IUPAC has been run by different committees with different responsibilities. These committees run different projects which include standardizing nomenclature, finding ways to bring chemistry to the world, IUPAC is best known for its works standardizing nomenclature in chemistry and other fields of science, but IUPAC has publications in many fields including chemistry, biology and physics. IUPAC is also known for standardizing the atomic weights of the elements through one of its oldest standing committees, the need for an international standard for chemistry was first addressed in 1860 by a committee headed by German scientist Friedrich August Kekulé von Stradonitz. This committee was the first international conference to create an international naming system for organic compounds, the ideas that were formulated in that conference evolved into the official IUPAC nomenclature of organic chemistry. IUPAC stands as a legacy of this meeting, making it one of the most important historical international collaborations of chemistry societies, since this time, IUPAC has been the official organization held with the responsibility of updating and maintaining official organic nomenclature. IUPAC as such was established in 1919, one notable country excluded from this early IUPAC is Germany. Germanys exclusion was a result of prejudice towards Germans by the Allied powers after World War I, Germany was finally admitted into IUPAC during 1929. However, Nazi Germany was removed from IUPAC during World War II, during World War II, IUPAC was affiliated with the Allied powers, but had little involvement during the war effort itself. After the war, East and West Germany were eventually readmitted to IUPAC, since World War II, IUPAC has been focused on standardizing nomenclature and methods in science without interruption. In 2016, IUPAC denounced the use of chlorine as a chemical weapon, the letter stated, Our organizations deplore the use of chlorine in this manner. According to the CWC, the use, stockpiling, distribution, IUPAC is governed by several committees that all have different responsibilities. Each committee is made up of members of different National Adhering Organizations from different countries, the steering committee hierarchy for IUPAC is as follows, All committees have an allotted budget to which they must adhere. Any committee may start a project, if a projects spending becomes too much for a committee to continue funding, it must take the issue to the Project Committee
7.
Ring strain
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In organic chemistry, ring strain is a type of instability that exists when bonds in a molecule form angles that are abnormal. Strain is most commonly discussed for small rings such as cyclopropanes and cyclobutanes, because of their high strain, the heat of combustion for these small rings is elevated. Ring strain results from a combination of angle strain, conformational strain or Pitzer strain, the simplest examples of angle strain are small cycloalkanes such as cyclopropane and cyclobutane. Furthermore, there is often eclipsing in cyclic systems which cannot be relieved, in alkanes, optimum overlap of atomic orbitals is achieved at 109. 5°. The most common compounds have five or six carbons in their ring. Adolf von Baeyer received a Nobel Prize in 1905 for the discovery of the Baeyer strain theory, angle strain occurs when bond angles deviate from the ideal bond angles to achieve maximum bond strength in a specific chemical conformation. Angle strain typically affects cyclic molecules, which lack the flexibility of acyclic molecules, angle strain destabilizes a molecule, as manifested in higher reactivity and elevated heat of combustion. Maximum bond strength results from effective overlap of orbitals in a chemical bond. A quantitative measure for angle strain is strain energy, angle strain and torsional strain combine to create ring strain that affects cyclic molecules. ΔHcombustion per CH2 -658.6 kJ = strain per CH2 The value 658.6 kJ per mole is obtained from an unstrained long-chain alkane, cyclic alkenes are subject to strain resulting from distortion of the sp2-hybridized carbon centers. Illustrative is C60 where the centres are pyramidalized. This distortion enhances the reactivity of this molecule, angle strain also is the basis of Bredts rule which dictates that bridgehead carbon centers are not incorporated in alkenes because the resulting alkene would be subject to extreme angle strain. In cycloalkanes, each carbon is bonded nonpolar covalently to two carbons and two hydrogen, the carbons have sp3 hybrization and should have ideal bond angles of 109. 5°. Due to the limitations of cyclic structure, however, the angle is only achieved in a six carbon ring — cyclohexane in chair conformation. For other cycloalkanes, the bond angles deviate from ideal, in cyclopropanes and cyclobutanes the C-C bonds are 60° and ~90° respectively. These molecules have bond angles between ring atoms which are more acute than the tetrahedral and trigonal planar bond angles required by their respective sp3. Because of the bond angles, the bonds have higher energy. In addition, the structures of cyclopropanes/enes and cyclclobutanes/enes offer very little conformational flexibility
8.
Borirane
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Borirane is the organic compound with the formula BC 2H5. This means that it is composed of 2 alkyl groups attached to a moiety in a cyclic shape. This colourless, flammable gas is the simplest borirane, a ring consisting of two carbon and one boron atom
9.
Aziridine
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Aziridines are organic compounds containing the aziridine functional group, a three-membered heterocycle with one amine group and two methylene bridges. The parent compound is aziridine, with molecular formula C 2H 5N, a banana bond model explains bonding in such compounds. Aziridine is less basic than acyclic aliphatic amines, with a pKa of 7.9 for the conjugate acid, angle strain in aziridine also increases the barrier to nitrogen inversion. This barrier height permits the isolation of separate invertomers, for example the cis, there are several syntheses of aziridines. An amine functional group displaces the adjacent halide in a nucleophilic substitution reaction to generate an aziridine. Amino alcohols have the reactivity, but the hydroxy group must first be converted into a good leaving group. The cyclization of an alcohol is called a Wenker synthesis. Nitrene addition to alkenes is a method for the synthesis of aziridines. Photolysis or thermolysis of azides are good ways to generate nitrenes, nitrenes can also be prepared in situ from iodosobenzene diacetate and sulfonamides, or the ethoxycarbonylnitrene from the N-sulfonyloxy precursor. Thermal treatment or photolysis of triazolines expels nitrogen, producing an aziridine, triazolines can be generated by cycloaddition of alkenes with an azide. This method is simple with excellent yield. Phe-Aziridine-Me can then undergo a ring opening reaction to form dextroamphetamine and levoamphetamine. Aziridines are reactive substrates in ring-opening reactions with nucleophiles due to their ring strain. Alcoholysis and aminolysis are basically the reverse reactions of the cyclizations, carbon nucleophiles such as organolithium reagents and organocuprates are also effective. These ylides can be trapped with a suitable dipolarophile in a 1, in this way 2-phenyl-N-tosylaziridine reacts with alkynes, nitriles, ketones and alkenes. N-unsubstituted aziridines can be opened with olefins in the presence of strong Lewis acid B3, the toxicology of a particular aziridine compound depends on its structure and activity, although sharing the general characteristics of aziridines. As electrophiles, aziridines are subject to attack and ring-opening by endogenous nucleophiles such as bases in DNA base pairs. Some reports note that the use of gloves has not prevented permeation of aziridine and it is therefore important that users check the breakthrough permeation times for gloves, and pay scrupulous attention to avoiding contamination when degloving
10.
Azirine
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Azirines are three membered heterocyclic unsaturated compounds containing a nitrogen atom and related to the saturated analogue aziridine. They are highly reactive yet have reported in a few products such as Dysidazirine. There are two isomers of azirine, 1H-azirines with a double bond are not stable and rearrange to the tautomeric 2H-azirine. 2H-Azirines can be considered strained imines and are isolable, 2H-Azirines are most often obtained by the thermolysis of vinyl azides. During this reaction, a nitrene is formed as an intermediate, alternatively, they can be obtained by oxidation of the corresponding aziridine. Photolysis of azirines is an efficient way to generate nitrile ylides. These nitrile ylides are dipolar compounds and can be trapped by a variety of dipolarophiles to yield heterocyclic compounds, the strained ring system also undergoes reactions that favor ring opening and can act as a nucleophile or an electrophile. An azirine is an intermediate in the Neber rearrangement
11.
Epoxide
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An epoxide is a cyclic ether with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained and they are produced on a large scale for many applications. In general, low molecular weight epoxides are colourless and nonpolar, a compound containing the epoxide functional group can be called an epoxy, epoxide, oxirane, and ethoxyline. Simple epoxides are often referred to as oxides, thus, the epoxide of ethylene is ethylene oxide. Many compounds have trivial names, ethylene oxide is called oxirane, some names emphasize the presence of the epoxide functional group, as in the compound 1, 2-epoxycycloheptane, which can also be called 1, 2-heptene oxide. A polymer formed from epoxide precursors is called an epoxy, the dominant epoxides industrially are ethylene oxide and propylene oxide, which are produced respectively on the scales of approximately 15 and 3 million tonnes/year. Other alkenes fail to react usefully, even propylene, many epoxides are generated by treating alkenes with peroxide-containing reagents, which donate a single oxygen atom. Outside of the scale, the main challenge with this approach is that typical peroxides are more valuable than the product epoxides. For this reason, this methodology is restricted to fine chemical applications, metal complexes are useful catalysts for these reactions. Typical peroxide reagents include hydrogen peroxide, peroxycarboxylic acids, and alkyl hydroperoxides, in specialized applications, other peroxide-containing reagents are employed, such as dimethyldioxirane. Depending on the mechanism of the reaction and the geometry of the starting material. In addition, if there are other stereocenters present in the starting material, the metal-catalyzed epoxidation was first explored using tert-butyl hydroperoxide as a source of an O atom. Association of TBHP with the metal generates the active metal catalyst with a peroxy ligand and this approach is used for the production of propylene oxide from propylene using various catalysts. Both t-butyl hydroperoxide or ethylbenzene hydroperoxide can be used as oxygen sources, more typically for laboratory operations, the Prilezhaev reaction is employed. This approach involves the oxidation of the alkene with a such as m-CPBA. Illustrative is the epoxidation of styrene with perbenzoic acid to styrene oxide, the peroxide is viewed as an electrophile, and the alkene a nucleophile. The reaction is considered to be concerted. The butterfly mechanism allows ideal positioning of the O-O sigma star orbital for C-C Pi electrons to attack, hydroperoxides are also employed in catalytic enantioselective epoxidations, such as the Sharpless epoxidation and the Jacobsen epoxidation. Together with the Shi epoxidation, these reactions are useful for the synthesis of chiral epoxides
12.
Episulfide
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Episulfides are a class of organic compounds that contain a saturated heterocyclic ring consisting of two carbon atoms and one sulfur atom. It is the analogue of an epoxide or aziridine. They are also known as thiiranes, olefin sulfides, thioalkylene oxides, most preparations of episulfides utilize a two-step method, converting an olefin to an epoxide before its conversion to the episulfide using either thiocyanate or thiourea. Common uses of episulfides in both academic and industrial settings most often involve their use as monomers in polymerization reactions, a number of chemists in the early 1900s, including Staudinger and Pfenninger, as well as Delepine, were the first to prepare and report episulfides. However, both of these accounts were isolated incidents on single substrates, in addition, a reaction analogous to epoxidation has been reported involving the metal-catalyzed reaction of sulfur with alkenes. Alkene + S → episulfide Episulfides have a ring strain due to the nature of three-membered rings. Therefore, most reactions of episulfides involve the anionic nucleophilic opening of the heterocyclic ring, nucleophiles that can be used include anionic hydride, sulfur, oxygen, nitrogen, and carbon. In large part, episulfides are less common than epoxides simply due to the common appearance of oxygen in natural products. However, episulfides have also found to be much less stable than epoxides. This destabilization is due to the nucleophilic character of sulfur. The few industrial processes involving episulfides take advantage of their extreme reactivity, for instance, one process has been patented which describes the use of episulfide monomers to produce high-refractive-index plastic lenses. While the exact polymerization reaction is unreported in the patent, a reaction involving the polymerization of episulfide monomers using Cl/CrCl as the catalyst has been reported
13.
Diaziridine
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Diaziridines are heterocyclic compounds containing two nitrogen atoms in a three-membered ring. They can be considered as strained hydrazines, due to the ring strain, the nitrogen atoms are configuration stable leading to cis-trans isomers. The final step is based on the cyclization of an aminal. Unsubstituted diaziridines are often directly oxidized to the more stable diazirines and they can undergo ring expansion reaction with electrophilic reagents like ketenes or isocyanates
14.
Diazirine
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Diazirines are a class of organic molecules consisting of a carbon bound to two nitrogen atoms, which are double-bonded to each other, forming a cyclopropene-like ring. Upon irradiation with light, diazirines form reactive carbenes, which can insert into C-H, N-H. Hence, diazirines have grown in popularity as small photo-reactive crosslinking reagents and they are often used in photoaffinity labeling studies to observe a variety of interactions, including ligand-receptor, ligand-enzyme, protein-protein, and protein-nucleic acid interactions. A number of methods exist in the literature for the preparation of diazirines, generally, synthetic schemes that begin with ketones involve conversion of the ketone with the desired substituents to diaziridines. These diaziridenes are then oxidized to form the desired diazirines. Diaziridines can be prepared from ketones by oximation, followed by tosylation, generally, oximation reactions are performed by reacting the ketone with hydroxylammonium chloride under heat in the presence of a base such as pyridine. Subsequent tosylation or mesylation of the alpha substituted oxygen with tosyl or mesyl chloride in the presence of base yields the tosyl or mesyl oxime, the final treatment of the tosyl or mesyl oxime with ammonia produces the diaziridine. Alternatively, diaziridines can be produced directly by the reaction of ketones with ammonia in the presence of an agent such as a chloramine or hydroxyl amine O-sulfonic acid. Diaziridines can be oxidized to diazirines by a number of methods, alternatively, diazirines can be formed in a one-pot process using the Graham reaction. In these schemes, amidines can be converted to diazirines by hypohalite oxidation. This reaction yields a halogenated diazirine, which can further be modified, the resulting aforementioned halodiazirine can undergo an exchange reaction to further functionalize the diazirene. Upon irradiation with UV light, diazirines form reactive carbene species, the carbene may exist in the singlet form, in which the two free electrons occupy the same orbital, or the triplet form, with two unpaired electrons in different orbitals. The substituents on the diazirine affect which carbene species is generated upon irradiation, diazirine substituents that are electron donating in nature can donate electron density to the empty p-orbital of the carbene that will be formed, and hence can stabilize the singlet state. For example, phenyldiazirine produces phenylcarbene in the singlet carbene state whereas p-nitrophenylchlorodiazirine or triflourophenyldiazirine produce the respective triplet carbene products, on the other hand, triflouroaryldiazirines in particular show favorable stability and photolytic qualities and are most commonly used in biological applications. Carbenes produced from diazirines are quickly quenched by reaction with water molecules, yet, as this feature minimizes unspecific labeling, it is actually an advantage of using diazirines. Diazirines are often used as crosslinking reagents, as the reactive carbenes they form upon irradiation with UV light can insert into C-H, N-H. This results in proximity dependent labeling of other species with the diazirine containing compound, aryl azides require a low wavelength of irradiation, which can damage the biological macromolecules under investigation. Diazirines are widely used in receptor labeling studies and this is because diazirine-containing analogs of various ligands can be synthesized and incubated with their respective receptors, and then subsequently exposed to light to produce reactive carbenes
15.
Oxaziridine
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An oxaziridine is an organic molecule that features a three-membered heterocycle containing oxygen, nitrogen, and carbon. In their largest application, oxazidines are intermediates in the production of hydrazine. Oxaziridines also serve as precursors to amides and participate in cycloadditions with various heterocumulenes to form substituted five-membered heterocycles, chiral oxaziridine derivatives effect asymmetric oxygen transfer to prochiral enolates as well as other substrates. Some oxaziridines also have the property of a barrier to inversion of the nitrogen. Oxaziridine derivatives were first reported in the mid-1950s by Emmons and subsequently by Krimm and Horner, whereas oxygen and nitrogen typically act as nucleophiles due to their high electronegativity, oxaziridines allow for electrophilic transfer of both heteroatoms. This unusual reactivity is due to the presence of the strained three membered ring and the relatively weak N-O bond. Nucleophiles tend to attack at the aziridine nitrogen when the substituent is small. The Peroxide process for the production of hydrazine through the oxidation of ammonia with hydrogen peroxide in the presence of ketones was developed in the early 1970s. Chiral camphorsulfonyloxaziridines proved useful in the syntheses of natural product. Both the Holton Taxol total synthesis and the Wender Taxol total synthesis feature asymmetric α-hydroxylation with camphorsulfonyloxaziridine, the two main approaches to synthesis of N-H, N-alkyl, and N-aryloxaziridines are oxidation of imines with peracids and amination of carbonyls. Additionally, oxidation of imines and oxidation of imines with chiral peracids may yield enantiopure oxaziridines. Some oxaziridines have the property of configurationally stable nitrogen atoms at room temperature due to an inversion barrier of 24 to 31 kcal/mol. Enantiopure oxaziridines where stereochemistry is entirely due to configurationally stable nitrogen are reported, while originally synthesized with mCPBA and the phase transfer catalyst benzyltrimethylammonium chloride, an improved synthesis using oxone as the oxidant is now most prevalent. Many N-sulfonyloxaziridines are used today, each slightly different properties. These reagents are summarized in the table below, with highly electron withdrawing perfluoroalkyl substituents, oxaziridines exhibit reactivity more similar to that of dioxiranes than typical oxaziridines. Notably, perfluoroalkyloxaziridines hydroxylate certain C-H bonds with high selectivity, perfluorinated oxaziridines may be synthesized by subjecting a perfluorinated imine to perfluoromethyl fluorocarbonyl peroxide and a metal fluoride to act as an HF scavenger. Oxaziridines are intermediates in the Peroxide process for the production of hydrazine, α-Hydroxyketones have been synthesized in many ways, including reduction of α-diketones, substitution of a hydroxyl for a leaving group and direct oxidation of an enolate. Oxodiperoxymolybdenum- and N-sulfonyloxaziridines are the most common sources of oxygen implemented in this process
16.
Dioxirane
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In chemistry dioxirane is a heterocyclic compound composed of one carbon and two oxygen atoms, it may be thought of as the smallest cyclic organic peroxide. The compound is unstable and has never been observed at room temperature. Difluorodioxirane, a gas, is one of the very few dioxirane derivatives that is stable in pure form at room temperature and its formation is thought to be radical in nature, preceding via a Criegee intermediate. Microwave analysis has indicated C-H, C-O and O-O bond lengths of 1.090,1.388 and 1.516 Å respectively, the very long and weak O-O bond is the origin of its instability
17.
Azetidine
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Azetidine is a saturated heterocyclic organic compound containing three carbon atoms and one nitrogen atom. It is a liquid at room temperature with an odor of ammonia and is strongly basic compared to most secondary amines. Azetidines do not occur as frequently in nature and have been studied far less closely related chemical compounds such as pyrrolidine. Azetidine and its derivatives are relatively rare structural motifs in natural products, notably, they are a key component of mugineic acids and penaresidins. Perhaps the most abundant azetidine containing natural product is azetidine-2-carboxylic acid, azete, the unsaturated analog Pubchem ChemSynthesis
18.
Oxetane
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Oxetane, or 1, 3-propylene oxide, is an heterocyclic organic compound with the molecular formula C3H6O, having a four-membered ring with three carbon atoms and one oxygen atom. The term oxetane may also more generally to any organic compound containing an oxetane ring. Other possible reactions to form oxetane ring is the Paternò–Büchi reaction, the oxetane ring can also be formed through diol cyclization as well as through decarboxylation of a six-membered cyclic carbonate. Paclitaxel is an example of a product containing an oxetane ring. Taxol has become a point of interest among researchers due to its unusual structure
19.
Thiete
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Thiete is a heterocyclic compound containing an unsaturated four-membered ring with three carbon atoms and one sulfur atom. It is more commonly encountered not on its own, but in anellated derivatives, thietes are generally not very stable. Thiete is an isomer of the unknown compound thioacrolein Thiete has been shown to be planar. Benzothietes are thietes annulated to benzo group, such species are prepared by flash vacuum pyrolysis of 2-mercaptobenzyl alcohols. They are precursors to other S-heterocycles, Thiete 1, 1-dioxides are sulfones, the parent being C3H4SO2. They are more stable than the parent thietes, substituted thiete-1, 1-dioxides can also be prepared by cycloaddition of sulfenes and ynamines
20.
Dithietane
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Dithietanes are saturated heterocyclic compounds that contain two divalent sulfur atoms and two sp3-hybridized carbon centers. Two isomers are possible for class of organosulfur compounds,1, 2-dithietanes. The first stable 1, 2-dithietane to be reported was the so-called dithiatopazine formed by intramolecular photodimerization of a dithiocarbonyl compound,1, 2-Dithietanes are to be distinguished from 1, 2-dithietes, containing two adjacent sulfur atoms and two sp2-hybridized carbon centers. A stable 1, 2-dithietane derivative is trans-3, 4-diethyl-1, 2-dithietane 1, 1-dioxide, formed by the dimerization of the lachrymatory agent syn-propanethial-S-oxide. 1, 3-dithietanes, where the atoms are non-adjacent. Carbon-substituted 1, 3-dithietanes are well known, with the first examples being described as early as 1872, examples include 2,2,4, 4-tetrachloro-1, 3-dithietane, the photochemically-formed dimer of thiophosgene, and tetrakis-1, 3-dithietane,2. Oxidized forms of 1, 3-dithietane are well known, although they are not prepared from the dithietane. Examples include the so-called zwiebelanes from onion volatiles and 1, 3-dithietane 1,1,3, 3-tetraoxide, the so-called sulfene dimer
21.
Dithiete
–
Dithiete is an unsaturated heterocyclic compound that contains two adjacent sulfur atoms and two sp2-hybridized carbon centers. Derivatives are known collectively as dithietes or 1, 2-dithietes, with 6 π electrons,1, 2-dithietes, like thiophenes, are examples of aromatic organosulfur compounds. Quantum chemical calculations can reproduce the observed stability of 1
22.
Aromaticity
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Aromatic molecules are very stable, and do not break apart easily to react with other substances. Organic compounds that are not aromatic are classified as aliphatic compounds—they might be cyclic, since the most common aromatic compounds are derivatives of benzene, the word “aromatic” occasionally refers informally to benzene derivatives, and so it was first defined. Nevertheless, many aromatic compounds exist. In living organisms, for example, the most common aromatic rings are the bases in RNA and DNA. An aromatic functional group or other substituent is called an aryl group, the earliest use of the term aromatic was in an article by August Wilhelm Hofmann in 1855. Hofmann used the term for a class of compounds, many of which have odors. In terms of the nature of the molecule, aromaticity describes a conjugated system often made of alternating single and double bonds in a ring. This configuration allows for the electrons in the pi system to be delocalized around the ring, increasing the molecules stability. The molecule cannot be represented by one structure, but rather a hybrid of different structures. These molecules cannot be found in one of these representations, with the longer single bonds in one location. Rather, the molecule exhibits bond lengths in between those of single and double bonds and this commonly seen model of aromatic rings, namely the idea that benzene was formed from a six-membered carbon ring with alternating single and double bonds, was developed by August Kekulé. The model for benzene consists of two forms, which corresponds to the double and single bonds superimposing to produce six one-and-a-half bonds. Benzene is a stable molecule than would be expected without accounting for charge delocalization. As is standard for resonance diagrams, the use of an arrow indicates that two structures are not distinct entities but merely hypothetical possibilities. Neither is a representation of the actual compound, which is best represented by a hybrid of these structures. A C=C bond is shorter than a C−C bond, but benzene is perfectly hexagonal—all six carbon–carbon bonds have the same length, intermediate between that of a single and that of a double bond. In a cyclic molecule with three alternating double bonds, cyclohexatriene, the length of the single bond would be 1.54 Å. However, in a molecule of benzene, the length of each of the bonds is 1.40 Å, a better representation is that of the circular π-bond, in which the electron density is evenly distributed through a π-bond above and below the ring
23.
Antimony
–
Antimony is a chemical element with symbol Sb and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite, Antimony compounds have been known since ancient times and were powdered for use as medicine and cosmetics, often known by the Arabic name, kohl. Metallic antimony was known, but it was erroneously identified as lead upon its discovery. In the West, it was first isolated by Vannoccio Biringuccio, for some time, China has been the largest producer of antimony and its compounds, with most production coming from the Xikuangshan Mine in Hunan. The industrial methods for refining antimony are roasting and reduction with carbon or direct reduction of stibnite with iron, the largest applications for metallic antimony is an alloy with lead and tin and the lead antimony plates in lead–acid batteries. Alloys of lead and tin with antimony have improved properties for solders, bullets, Antimony compounds are prominent additives for chlorine and bromine-containing fire retardants found in many commercial and domestic products. An emerging application is the use of antimony in microelectronics, Antimony is in a pnictogen and has an electronegativity of 2.05. In accordance with periodic trends, it is more electronegative than tin or bismuth, Antimony is stable in air at room temperature, but reacts with oxygen if heated to produce antimony trioxide, Sb2O3. Antimony is resistant to attack by acids, four allotropes of antimony are known, a stable metallic form and three metastable forms. Elemental antimony is a brittle, silver-white shiny metalloid, when slowly cooled, molten antimony crystallizes in a trigonal cell, isomorphic with the gray allotrope of arsenic. A rare explosive form of antimony can be formed from the electrolysis of antimony trichloride, when scratched with a sharp implement, an exothermic reaction occurs and white fumes are given off as metallic antimony forms, when rubbed with a pestle in a mortar, a strong detonation occurs. Black antimony is formed upon cooling of antimony vapor. It has the crystal structure as red phosphorus and black arsenic, it oxidizes in air. At 100 °C, it transforms into the stable form. The yellow allotrope of antimony is the most unstable and it has only been generated by oxidation of stibine at −90 °C. Above this temperature and in ambient light, this metastable allotrope transforms into the more stable black allotrope, elemental antimony adopts a layered structure in which layers consist of fused, ruffled, six-membered rings. The nearest and next-nearest neighbors form an octahedral complex, with the three atoms in each double layer slightly closer than the three atoms in the next. This relatively close packing leads to a density of 6.697 g/cm3
24.
Stibole
–
Stibole is a theoretical heterocyclic organic compound, a five-membered ring with the formula C4H4SbH. It is classified as a metallole and it can be viewed as a structural analog of pyrrole, with antimony replacing the nitrogen atom of pyrrole. Substituted derivatives, which have been synthesized, are called stiboles,2, 5-Dimethyl-1-phenyl-1H-stibole, for example, can be formed by the reaction of 1, 1-dibutyl-2, 5-dimethylstannole and dichlorophenylstibine. Stiboles can be used to form ferrocene-like sandwich compounds
25.
Arsenic
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Arsenic is a chemical element with symbol As and atomic number 33. Arsenic occurs in minerals, usually in combination with sulfur and metals. It has various allotropes, but only the form is important to industry. The primary use of arsenic is in alloys of lead. Arsenic is a common dopant in semiconductor electronic devices. Arsenic and its compounds, especially the trioxide, are used in the production of pesticides, treated wood products, herbicides, a few species of bacteria are able to use arsenic compounds as respiratory metabolites. Trace quantities of arsenic are a dietary element in rats, hamsters, goats, chickens. However, arsenic poisoning occurs in multicellular life if quantities are larger than needed, Arsenic contamination of groundwater is a problem that affects millions of people across the world. The three most common allotropes are metallic gray, yellow, and black arsenic, with gray being the most common. Gray arsenic adopts a structure consisting of many interlocked, ruffled, six-membered rings. Because of weak bonding between the layers, gray arsenic is brittle and has a relatively low Mohs hardness of 3.5. Nearest and next-nearest neighbors form an octahedral complex, with the three atoms in the same double-layer being slightly closer than the three atoms in the next. This relatively close packing leads to a density of 5.73 g/cm3. Gray arsenic is a semimetal, but becomes a semiconductor with a bandgap of 1. 2–1.4 eV if amorphized, gray arsenic is also the most stable form. Yellow arsenic is soft and waxy, and somewhat similar to tetraphosphorus, both have four atoms arranged in a tetrahedral structure in which each atom is bound to each of the other three atoms by a single bond. This unstable allotrope, being molecular, is the most volatile, least dense, solid yellow arsenic is produced by rapid cooling of arsenic vapor, As 4. It is rapidly transformed into gray arsenic by light, the yellow form has a density of 1.97 g/cm3. Black arsenic is similar in structure to red phosphorus, black arsenic can also be formed by cooling vapor at around 100–220 °C
26.
Arsole
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Arsole, also called arsenole or arsacyclopentadiene, is an organoarsenic compound with the formula C4H4AsH. It is classified as a metallole and is isoelectronic to and related to pyrrole except that an atom is substituted for the nitrogen atom. Whereas the pyrrole molecule is planar, the molecule is not. Arsole is only moderately aromatic, with about 40% the aromaticity of pyrrole, arsole itself has not been reported in pure form, but several substituted analogs called arsoles exist. Arsoles and more complex arsole derivatives have similar structure and chemical properties to those of phosphole derivatives, when arsole is fused to a benzene ring, this molecule is called arsindole, or benzarsole. Arsole belongs to the series of heterocyclic pnictogen compounds, however, this silly name coincidence has also stimulated detailed scientific studies. Arsole itself has not been isolated experimentally yet, but the molecular geometry, the situation is similar for other C4H4MH metalloles where M = P, As, Sb and Bi. Calculations suggest that whereas pyrrole molecule is planar, phosphole and heavier metalloles are not, a similar tendency is predicted for the fluorinated C4F4MH derivatives, but the inversion barriers are about 50–100% higher. The planarity is lost even in pyrrole when its nitrogen-bonded hydrogen atom is substituted, however, non-zero value of this energy does not necessarily mean the molecule has low symmetry, because of the possibility of thermal or quantum tunneling between the two configurations. Aromaticity of the arsole manifests itself in delocalization and resonance of its ring electrons and it is closely related to planarity in that the more planar the molecule the stronger its aromaticity. Aromaticity of arsole and its derivatives has been debated for both from experimental and theoretical point of view. A2005 review combined with quantum chemical calculations concluded that arsole itself is moderately aromatic as its current is 40% that of pyrrole. However, comparable ring current was calculated for cyclopentadiene, which has long regarded as non-aromatic. Other reports suggest that the aromaticity can vary between arsole derivatives, chemical properties of arsole derivatives have been studied experimentally, they are similar to those of phosphole and its derivatives. Substitution of all atoms in arsole with phenyl groups yields yellow needles of crystalline pentaphenylarsole. This complex can be prepared, at a yield of 50–93%, by reacting 1, 4-diiodo-1,2,3, 4-tetraphenylbutadiene or 1, 4-dilithio-1,2,3, pentaphenylarsole can further be oxidized with hydrogen peroxide resulting in yellow crystals with melting point of 252 °C. It can also be reacted with iron pentacarbonyl in isooctane at 150 °C to yield a solid organoarsenic compound with the formula C34H25As, reacting pentaphenylarsole with metallic lithium or potassium yields 1,2, 3-triphenyl naphthalene. Reaction of phenylarsenous dichloride with linear diphenyls results in 1,2, 5-triphenylarsole and this compound forms various anions upon treatment with alkali metals
27.
Bismuth
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Bismuth is a chemical element with the symbol Bi and atomic number 83. Bismuth, a pentavalent post-transition metal and one of the pnictogens, chemically resembles its lighter homologs arsenic, elemental bismuth may occur naturally, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead and it is a brittle metal with a silvery white color when freshly produced, but surface oxidation can give it a pink tinge. Bismuth is the most naturally diamagnetic element, and has one of the lowest values of thermal conductivity among metals, Bismuth metal has been known since ancient times, although it was often confused with lead and tin, which share some physical properties. Bismuth was long considered the element with the highest atomic mass that is stable, because of its tremendously long half-life, bismuth may still be considered stable for almost all purposes. Bismuth compounds account for half the production of bismuth. They are used in cosmetics, pigments, and a few pharmaceuticals, notably bismuth subsalicylate, bismuths unusual propensity to expand upon freezing is responsible for some of its uses, such as in casting of printing type. Bismuth has unusually low toxicity for a heavy metal, as the toxicity of lead has become more apparent in recent years, there is an increasing use of bismuth alloys as a replacement for lead. The name bismuth dates from around the 1660s, and is of uncertain etymology and it is one of the first 10 metals to have been discovered. Bismuth appears in the 1660s, from obsolete German Bismuth, Wismut, Wissmuth, the New Latin bisemutum is from the German Wismuth, perhaps from weiße Masse, white mass. The element was confused in early times with tin and lead because of its resemblance to those elements, Bismuth has been known since ancient times, so no one person is credited with its discovery. Agricola, in De Natura Fossilium states that bismuth is a metal in a family of metals including tin. This was based on observation of the metals and their physical properties, miners in the age of alchemy also gave bismuth the name tectum argenti, or silver being made, in the sense of silver still in the process of being formed within the Earth. Bismuth was also known to the Incas and used in a bronze alloy for knives. Bismuth is a metal with a white, silver-pink hue, often occurring in its native form. The spiral, stair-stepped structure of crystals is the result of a higher growth rate around the outside edges than on the inside edges. The variations in the thickness of the layer that forms on the surface of the crystal causes different wavelengths of light to interfere upon reflection. When burned in oxygen, bismuth burns with a blue flame and its toxicity is much lower than that of its neighbors in the periodic table, such as lead, antimony, and polonium
28.
Bismole
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Bismole is a theoretical heterocyclic organic compound, a five-membered ring with the formula C4H4BiH. It is classified as a metallole and it can be viewed as a structural analog of pyrrole, with bismuth replacing the nitrogen atom of pyrrole. The unsubstituted compound has not been isolated due to the energy of the Bi-H bond. Substituted derivatives, which have been synthesized, are called bismoles,2, 5-Bis-3, 4-dimethyl-1-phenyl-1H-bismole, for example, can be formed by the reaction of -1, 4-bis-1, 4-diiodobuta-2, 3-dimethyl-1, 3-diene and diiodophenylbismuthine. Bismoles can be used to form ferrocene-like sandwich compounds
29.
Boron
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Boron is a chemical element with symbol B and atomic number 5. Produced entirely by cosmic ray spallation and supernovae and not by stellar nucleosynthesis, it is an element in the Solar system. Boron is concentrated on Earth by the water-solubility of its more common naturally occurring compounds and these are mined industrially as evaporites, such as borax and kernite. The largest known deposits are in Turkey, the largest producer of boron minerals. Elemental boron is a metalloid that is found in small amounts in meteoroids, industrially, very pure boron is produced with difficulty because of refractory contamination by carbon or other elements. Several allotropes of boron exist, amorphous boron is a powder, crystalline boron is silvery to black, extremely hard. The primary use of boron is as boron filaments with applications similar to carbon fibers in some high-strength materials. Boron is primarily used in chemical compounds, about half of all consumption globally, boron is used as an additive in glass fibers of boron-containing fiberglass for insulation and structural materials. The next leading use is in polymers and ceramics in high-strength, lightweight structural, borosilicate glass is desired for its greater strength and thermal shock resistance than ordinary soda lime glass. Boron compounds are used as fertilizers in agriculture and in sodium perborate bleaches, a small amount of boron is used as a dopant in semiconductors, and reagent intermediates in the synthesis of organic fine chemicals. A few boron-containing organic pharmaceuticals are used or are in study, natural boron is composed of two stable isotopes, one of which has a number of uses as a neutron-capturing agent. In biology, borates have low toxicity in mammals, but are toxic to arthropods and are used as insecticides. Boric acid is mildly antimicrobial, and several natural boron-containing organic antibiotics are known, small amounts of boron compounds play a strengthening role in the cell walls of all plants, making boron a necessary plant nutrient. Boron is involved in the metabolism of calcium in both plants and animals and it is considered an essential nutrient for humans, and boron deficiency is implicated in osteoporosis. The word boron was coined from borax, the mineral from which it was isolated, by analogy with carbon, marco Polo brought some glazes back to Italy in the 13th century. Agricola, around 1600, reports the use of borax as a flux in metallurgy, in 1777, boric acid was recognized in the hot springs near Florence, Italy, and became known as sal sedativum, with primarily medical uses. The rare mineral is called sassolite, which is found at Sasso, Sasso was the main source of European borax from 1827 to 1872, when American sources replaced it. Boron compounds were relatively rarely used until the late 1800s when Francis Marion Smiths Pacific Coast Borax Company first popularized and produced them in volume at low cost
30.
Borole
–
Borole is a theoretical heterocyclic organic compound, a five-membered ring with the formula C4H4BH. It is classified as a metallole and it can be viewed as a structural analog of pyrrole, with boron replacing the nitrogen atom of pyrrole. The unsubstituted compound has not been isolated, substituted derivatives, which have been synthesized, are called boroles. Although the Hückels rule cannot be applied to borole, it is considered to be anti-aromatic. The first borole to be isolated, pentaphenylborole, can be formed by the reaction of 1, 1-dimethyl-2,3,4, 5-tetraphenylstannole, boroles can be used to form ferrocene-like sandwich compounds
31.
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
32.
Pyrrolidine
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Pyrrolidine, also known as tetrahydropyrrole, is an organic compound with the molecular formula 4NH. It is a secondary amine, also classified as a saturated heterocycle. It is a liquid that is miscible with water and most organic solvents. It has an ammonia-like, but characteristic odor, in addition to pyrrolidine itself, many substituted pyrrolidines are known. Pyrrolidine is produced by treatment of 1, 4-butanediol with ammonia over an oxide catalyst, many modifications of pyrrolidine are found in natural and synthetic chemistry. The pyrrolidine ring structure is present in numerous natural alkaloids such as nicotine and hygrine and it is found in many drugs such as procyclidine and bepridil. It also forms the basis for the racetam compounds, the amino acids proline and hydroxyproline are, in a structural sense, derivatives of pyrrolidine. Its basicity is typical of other dialkyl amines, relative to many secondary amines, pyrrolidine is distinctive because of its compactness, a consequence of its cyclic structure. Pyrrolidine is used as a block in the synthesis of more complex organic compounds. It is used to activate ketones and aldehydes toward nucleophilic addition by formation of enamines
33.
Pyrrole
–
Pyrrole is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4H4NH. It is a volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e. g. N-methylpyrrole, porphobilinogen, a trisubstituted pyrrole, is the biosynthetic precursor to many natural products such as heme. Pyrroles are components of more complex macrocycles, including the porphyrins of heme, the chlorins, bacteriochlorins, chlorophyll, Pyrrole is a colorless volatile liquid that darkens readily upon exposure to air, and is usually purified by distillation immediately before use. Pyrrole is a 5-membered aromatic heterocycle, like furan and thiophene, unlike furan and thiophene, it has a dipole in which the positive end lies on the side of the heteroatom, with a dipole moment of 1.58 D. In CDCl3, it has chemical shifts at 6.68 and 6.22, Pyrrole is weakly basic, with a conjugate acid pKa of −3.8. The most thermodynamically stable pyrrolium cation is formed by protonation at the 2 position, Substitution of pyrrole with alkyl substituents provides a more basic molecule—for example, tetramethylpyrrole has a conjugate acid pKa of +3.7. Pyrrole is also weakly acidic at the N–H position, with a pKa of 17.5, Pyrrole was first detected by F. F. Runge in 1834, as a constituent of coal tar. In 1857, it was isolated from the pyrolysate of bone and its name comes from the Greek pyrrhos, from the reaction used to detect it—the red color that it imparts to wood when moistened with hydrochloric acid. Pyrrole itself is not naturally occurring, but many of its derivatives are found in a variety of cofactors, other pyrrole-containing secondary metabolites include PQQ, makaluvamine M, ryanodine, rhazinilam, lamellarin, prodigiosin, myrmicarin, and sceptrin. The syntheses of pyrrole-containing haemin, synthesized by Emil Fischer was recognized by the Nobel Prize, Pyrrole is a constituent of tobacco smoke and not as an ingredient. Pyrrole is prepared industrially by treatment of furan with ammonia in the presence of acid catalysts, like SiO2. Pyrrole can also be formed by dehydrogenation of pyrrolidine. Several syntheses of the ring have been described. The Hantzsch pyrrole synthesis is the reaction of β-ketoesters with ammonia, the Knorr pyrrole synthesis involves the reaction of an α-amino ketone or an α-amino-β-ketoester with an activated methylene compound. The method involves the reaction of an α-aminoketone and a compound containing a methylene group α to a carbonyl group, in the Paal–Knorr pyrrole synthesis, a 1, 4-dicarbonyl compound reacts with ammonia or a primary amine to form a substituted pyrrole. The Van Leusen reaction can be used to form pyrroles, by reaction of tosylmethyl isocyanide with an enone in the presence of base, a 5-endo cyclization then forms the 5-membered ring, which reacts to eliminate the tosyl group. The last step is tautomerization to the pyrrole, the Barton–Zard synthesis proceeds in a manner similar to the Van Leusen synthesis
34.
Oxygen
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Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog. At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products
35.
Tetrahydrofuran
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Tetrahydrofuran, whose preferred IUPAC name was changed in 2013 to oxolane, is an organic compound with the formula 4O. The compound is classified as heterocyclic compound, specifically a cyclic ether and it is a colorless, water-miscible organic liquid with low viscosity. It is mainly used as a precursor to polymers, being polar and having a wide liquid range, THF is a versatile solvent. About 200,000 tonnes of tetrahydrofuran are produced annually, the most widely used industrial process involves the acid-catalyzed dehydration of 1, 4-butanediol. Ashland/ISP is one the biggest producers of this chemical route, the method is similar to the production of diethyl ether from ethanol. The butanediol is derived from condensation of acetylene with formaldehyde followed by hydrogenation, duPont developed a process for producing THF by oxidizing n-butane to crude maleic anhydride, followed by catalytic hydrogenation. A third major industrial route entails hydroformylation of allyl alcohol followed by hydrogenation to the butanediol, THF can also be synthesized by catalytic hydrogenation of furan. Certain sugars can be converted to THF, although this method is not widely practiced, furan is thus derivable from renewable resources. The other main application of THF is as a solvent for polyvinyl chloride. It is a solvent with a dielectric constant of 7.6. It is a polar solvent and can dissolve a wide range of nonpolar and polar chemical compounds. THF is water-miscible and can form solid clathrate hydrate structures with water at low temperatures, in the laboratory, THF is a popular solvent when its water miscibility is not an issue. It is more basic than diethyl ether and forms complexes with Li+, Mg2+. It is a solvent for hydroboration reactions and for organometallic compounds such as organolithium. Although similar to diethyl ether, THF is a stronger base, commercial THF contains substantial water that must be removed for sensitive operations, e. g. those involving organometallic compounds. Although THF is traditionally dried by distillation from an aggressive desiccant, aqueous THF augments the hydrolysis of glycans from biomass and dissolves the majority of biomass lignin making it a suitable solvent for biomass pretreatment. THF is often used in polymer science, for example, it can be used to dissolve polymers prior to determining their molecular mass using gel permeation chromatography. THF dissolves PVC as well, and thus it is the ingredient in PVC adhesives
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