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Cyclooctadecanonaene
Cyclooctadecanonaene or 8nnulene is an organic compound with chemical formula . It belongs to the class of highly conjugated compounds known as annulenes and is aromatic. The usual isomer that 8nnulene refers to is the most stable one, containing six interior hydrogens and twelve exterior ones, with the nine formal double bonds in the ''cis'',''trans'',''trans'',''cis'',''trans'',''trans'',''cis'',''trans'',''trans'' configuration. It is reported to be a red-brown crystalline solid. Aromaticity Notably, 8nnulene is the first annulene after benzene ( nnulene) to be fully aromatic: its π-system contains 4''n'' + 2 electrons (''n'' = 4), and it is large enough to comfortably accommodate six hydrogen atoms in its interior, allowing it to adopt a planar shape, thus satisfying Hückel's rule. The discovery of aromatic stabilization for 8nnulene is historically significant for confirming earlier theoretical predictions based on molecular orbital theory, since simple versions of vale ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Annulene
Annulenes are monocyclic hydrocarbons that contain the maximum number of non-cumulated or conjugated double bonds (' mancude'). They have the general formula CnHn (when ''n'' is an even number) or C''n''H''n''+1 (when ''n'' is an odd number). The IUPAC naming conventions are that annulenes with 7 or more carbon atoms are named as 'n''nnulene, where ''n'' is the number of carbon atoms in their ring, though sometimes the smaller annulenes are referred to using the same notation, and benzene is sometimes referred to simply as annulene. The first three even annulenes are cyclobutadiene, benzene, and cyclooctatetraene ( nnulene). Some annulenes, namely cyclobutadiene, cyclodecapentaene ( 0nnulene), cyclododecahexaene ( 2nnulene) and cyclotetradecaheptaene ( 4nnulene), are unstable, with cyclobutadiene extremely so. In the related annulynes, one double bond is replaced by a triple bond. Aromaticity Annulenes may be '' aromatic'' (benzene, nnulene and 8nnulene), ''non- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyclotetradecaheptaene
Cyclotetradecaheptaene, often referred to as 4nnulene, is a hydrocarbon with molecular formula C14H14, which played an important role in the development of criteria (Hückel's rule) for aromaticity, a stabilizing property of central importance in physical organic chemistry Physical organic chemistry, a term coined by Louis Hammett in 1940, refers to a discipline of organic chemistry that focuses on the relationship between chemical structures and reactivity, in particular, applying experimental tools of physical .... It forms dark-red needle-like crystals. Structure and aromaticity Although the conjugated ring of 4 nnulene contains 4''n''+2 electrons, it only exhibits limited evidence for being aromatic. It does not fully conform to Hückel's rule because none of its ''cis''/''trans'' isomers can adopt a completely planar conformation due to crowding of the interior hydrogens. There is evidence that it has two isomeric forms of comparable stability (''trans'', ''cis'', ' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hückel's Rule
In organic chemistry, Hückel's rule predicts that a planar ring molecule will have aromatic properties if it has 4''n'' + 2 π electrons, where ''n'' is a non-negative integer. The quantum mechanical basis for its formulation was first worked out by physical chemist Erich Hückel in 1931. The succinct expression as the 4''n'' + 2 rule has been attributed to W. v. E. Doering (1951), although several authors were using this form at around the same time. In agreement with the Möbius–Hückel concept, a cyclic ring molecule follows Hückel's rule when the number of its π-electrons equals 4''n'' + 2, although clearcut examples are really only established for values of ''n'' = 0 up to about ''n'' = 6. Hückel's rule was originally based on calculations using the Hückel method, although it can also be justified by considering a particle in a ring system, by the LCAO method and by the Pariser–Parr–Pople method. Aromat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organic Compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon- hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The study of the properties, reactions, and syntheses of organic compounds comprise the discipline known as organic chemistry. For historical reasons, a few classes of carbon-containing compounds (e.g., carbonate salts and cyanide salts), along with a few other exceptions (e.g., carbon dioxide, hydrogen cyanide), are not classified as organic compounds and are considered inorganic. Other than those just named, little consensus exists among chemists on precisely which carbon-containing compounds are excluded, making any rigorous definition of an organic compound elusive. Although organic compounds make up only a small percentage of Earth's crust, they are of central importance because all known life is based on organic compounds. Livin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Copper(II) Acetate
Copper(II) acetate, also referred to as cupric acetate, is the chemical compound with the formula Cu(OAc)2 where AcO− is acetate (). The hydrated derivative, Cu2(OAc)4(H2O)2, which contains one molecule of water for each copper atom, is available commercially. Anhydrous copper(II) acetate is a dark green crystalline solid, whereas Cu2(OAc)4(H2O)2 is more bluish-green. Since ancient times, copper acetates of some form have been used as fungicides and green pigments. Today, copper acetates are used as reagents for the synthesis of various inorganic and organic compounds. Copper acetate, like all copper compounds, emits a blue-green glow in a flame. Structure Copper acetate hydrate adopts the paddle wheel structure seen also for related Rh(II) and Cr(II) tetraacetates. One oxygen atom on each acetate is bound to one copper atom at 1.97 Å (197 pm). Completing the coordination sphere are two water ligands, with Cu–O distances of 2.20 Å (220 pm). The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Three-center Two-electron Bond
A three-center two-electron (3c–2e) bond is an electron-deficient chemical bond where three atoms share two electrons. The combination of three atomic orbitals form three molecular orbitals: one bonding, one ''non''-bonding, and one ''anti''-bonding. The two electrons go into the bonding orbital, resulting in a net bonding effect and constituting a chemical bond among all three atoms. In many common bonds of this type, the bonding orbital is shifted towards two of the three atoms instead of being spread equally among all three. Example molecules with 3c–2e bonds are the trihydrogen cation () and diborane (). In these two structures, the three atoms in each 3c-2e bond form an angular geometry, leading to a bent bond. Boranes and carboranes An extended version of the 3c–2e bond model features heavily in cluster compounds described by the polyhedral skeletal electron pair theory, such as boranes and carboranes. These molecules derive their stability from having a com ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Franz Sondheimer
Franz Sondheimer FRS (17 May 1926 – 11 February 1981) was a German-born British professor of chemistry. In 1960, he was awarded the Israel Prize for his contributions to science. Biography Franz Sondheimer was born in Stuttgart on 17 May 1926, the second son of Max and Ida Sondheimer. His father ran the family glue manufacturing business. His elder brother, Ernst, was Professor of Mathematics at Westfield College. Having business connections in England, Max Sondheimer managed to get his family to London in September 1937. Sondheimer, knowing no English, began his schooling in England first at Southend and then at Hailey School in Bournemouth. In 1940, having passed Common Entrance, he attended the part of Highgate School remaining in London, where he obtained School Certificate in nine subjects in 1942. A little over a year later he gained entrance to Imperial College, where he studied until the end of the war, coming top of his year in the final examination. He was awarded a P ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eglinton Reaction
The Glaser coupling is a type of coupling reaction. It is by far the oldest acetylenic coupling and is based on cuprous salts like copper(I) chloride or copper(I) bromide and an additional oxidant like oxygen. The base in its original scope is ammonia. The solvent is water or an alcohol. The reaction was first reported by in 1869. He suggested the following process for his way to diphenylbutadiyne: :CuCl + PhC2H + NH3 → PhC2Cu + NH4Cl :2PhC2Cu + O → PhC2C2Ph + Cu2O Modifications Eglinton reaction In the related Eglinton reaction two terminal alkynes are coupled by a copper(II) salt such as cupric acetate. :2R-\!\!-H -> ce\ce] R-\!\!-\!\!-R The oxidative coupling of alkynes has been used to synthesize a number of fungal antibiotics. The stoichiometry is represented by this highly simplified scheme: : Such reactions proceed via metal-alkyne complex, copper(I)-alkyne complexes. This methodology was used in the synthesis of cyclooctadecanonaene. Another example is the synt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alkyne
\ce \ce Acetylene \ce \ce \ce Propyne \ce \ce \ce \ce 1-Butyne In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and no other functional groups form a homologous series with the general chemical formula . Alkynes are traditionally known as acetylenes, although the name ''acetylene'' also refers specifically to , known formally as ethyne using IUPAC nomenclature. Like other hydrocarbons, alkynes are generally hydrophobic. Structure and bonding In acetylene, the H–C≡C bond angles are 180°. By virtue of this bond angle, alkynes are rod-like. Correspondingly, cyclic alkynes are rare. Benzyne cannot be isolated. The C≡C bond distance of 121 picometers is much shorter than the C=C distance in alkenes (134 pm) or the C–C bond in alkanes (153 pm). : The triple bond is very strong with a bond strength of 839 kJ/mol. The sigma bond contri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deprotonation
Deprotonation (or dehydronation) is the removal (transfer) of a proton (or hydron, or hydrogen cation), (H+) from a Brønsted–Lowry acid in an acid–base reaction.Henry Jakubowski, Biochemistry Online Chapter 2A3, https://employees.csbsju.edu/hjakubowski/classes/ch331/protstructure/PS_2A3_AA_Charges.html, accessed 12/2/2020 The species formed is the conjugate base of that acid. The complementary process, when a proton is added (transferred) to a Brønsted–Lowry base, is protonation (or hydronation). The species formed is the conjugate acid of that base. A species that can either accept or donate a proton is referred to as amphiprotic. An example is the H2O (water) molecule, which can gain a proton to form the hydronium ion, H3O+, or lose a proton, leaving the hydroxide ion, OH−. The relative ability of a molecule to give up a proton is measured by its p''K''a value. A low p''K''a value indicates that the compound is acidic and will easily give up its proton to a bas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pyridine
Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a distinctive, unpleasant fish-like smell. Pyridine is colorless, but older or impure samples can appear yellow, due to the formation of extended, unsaturated polymeric chains, which show significant electrical conductivity. The pyridine ring occurs in many important compounds, including agrochemicals, pharmaceuticals, and vitamins. Historically, pyridine was produced from coal tar. As of 2016, it is synthesized on the scale of about 20,000 tons per year worldwide. Properties Physical properties The molecular electric dipole moment is 2.2 debyes. Pyridine is diamagnetism, diamagnetic and has a Magnetic susceptibility, diamagnetic susceptibility of −48.7 × 10−6 cm3·mol−1. Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Friedel–Crafts Reaction
The Friedel–Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877 to attach substituents to an aromatic ring. Friedel–Crafts reactions are of two main types: alkylation reactions and acylation reactions. Both proceed by electrophilic aromatic substitution. Alkylation With alkyl halides Friedel–Crafts alkylation involves the alkylation of an aromatic ring. Traditionally, the alkylating agents are alkyl halides. Many alkylating agents can be used instead of alkyl halides. For example, enones and epoxides can be used in presence of protons. Traditionally also, the reaction employs a strong Lewis acid, such as aluminium chloride as catalyst. This reaction suffers from the disadvantage that the product is more nucleophilic than the reactant because alkyl groups are activators for the Friedel–Crafts reaction. Consequently, overalkylation can occur. Steric hindrance can be exploited to limit the number of alkylations, as in the ' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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