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Vicarious Nucleophilic Substitution
In organic chemistry, the vicarious nucleophilic substitution is a special type of nucleophilic aromatic substitution in which a nucleophile replaces a hydrogen atom on the aromatic ring and not leaving groups such as halogen substituents which are ordinarily encountered in SNAr. This reaction type was reviewed in 1987 by Polish chemists Mieczysław Mąkosza and Jerzy Winiarski.''Synthesis of heterocyclic compounds via vicarious nucleophilic substitution of hydrogen'' Mieczysław Mąkosza Pure Appl. Chem., Vol. 69, No. 3, pp. 559-564, 1997''Article link It is typically encountered with nitroarenes and especially with nucleophiles, resulting in alkylated arenes: the new substituent can take the ''ortho'' or ''para'' positions, reversing the selectivity for the ''meta'' position that is usually observed with such compounds under electrophilic substitution. Carbon nucleophiles carry an electron-withdrawing group and a leaving group: the nucleophile attacks the aromatic ring, and exc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organic Chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; Greeves, N. and Warren, S. (2012) ''Organic Chemistry''. Oxford University Press. pp. 1–15. . Study of structure determines their structural formula. Study of properties includes physical and chemical properties, and evaluation of chemical reactivity to understand their behavior. The study of organic reactions includes the chemical synthesis of natural products, drugs, and polymers, and study of individual organic molecules in the laboratory and via theoretical ( in silico) study. The range of chemicals studied in organic chemistry includes hydrocarbons (compounds containing only carbon and hydrogen) as well as compounds based on carbon, but also containing other elements, especially oxygen, nitrogen, sulfur, phosphorus (included in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nitrobenzene
Nitrobenzene is an organic compound with the chemical formula C6H5 NO2. It is a water-insoluble pale yellow oil with an almond-like odor. It freezes to give greenish-yellow crystals. It is produced on a large scale from benzene as a precursor to aniline. In the laboratory, it is occasionally used as a solvent, especially for electrophilic reagents. Production Nitrobenzene is prepared by nitration of benzene with a mixture of concentrated sulfuric acid, water, and nitric acid. This mixture is sometimes called "mixed acid." The production of nitrobenzene is one of the most dangerous processes conducted in the chemical industry because of the exothermicity of the reaction (Δ''H'' = −117 kJ/mol). World capacity for nitrobenzene in 1985 was about 1,700,000 tonnes. The nitration process involves formation of the nitronium ion (NO2+), followed by an electrophilic aromatic substitution reaction of it with benzene. The nitronium ion is generated by the reaction of nitric aci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aromaticity
In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to saturated compounds having single bonds, and other geometric or connective non-cyclic arrangements with the same set of atoms. Aromatic rings are very stable and do not break apart easily. Organic compounds that are not aromatic are classified as aliphatic compounds—they might be cyclic, but only aromatic rings have enhanced stability. The term ''aromaticity'' with this meaning is historically related to the concept of having an aroma, but is a distinct property from that meaning. Since the most common aromatic compounds are derivatives of benzene (an aromatic hydrocarbon common in petroleum and its distillates), the word ''aromatic'' occasionally refers informally to benzene derivatives, and so it was first defined. Nevertheless, many non-be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Elimination Reaction
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 two-step mechanism is known as the E1 reaction. The numbers refer not to the number of steps in the mechanism, but rather to the kinetics of the reaction: E2 is bimolecular (second-order) while E1 is unimolecular (first-order). In cases where the molecule is able to stabilize an anion but possesses a poor leaving group, a third type of reaction, E1CB, exists. Finally, the pyrolysis of xanthate and acetate esters proceed through an "internal" elimination mechanism, the Ei mechanism. E2 mechanism The E2 mechanism, where E2 stands for bimolecular elimination, involves a one-step mechanism in which ''carbon-hydrogen'' and ''carbon-halogen'' bonds break to form a double bond (''C=C Pi bond''). The specifics of the reaction are as follows: * E2 is a single step elimination, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron-withdrawing Group
In chemistry, an electron-withdrawing group (EWG) is a substituent that has some of the following kinetic and thermodynamic implications: *with regards to electron transfer, electron-withdrawing groups enhance the oxidizing power tendency of the appended species. Tetracyanoethylene is an oxidant because the alkene is appended to four cyano substituents, which are electron-withdrawing. *with regards to acid-base reactions, acids with electron-withdrawing groups species have low acid dissociation constants. For EWG's attached to benzene, this effect is described by the Hammett equation, which allows EWGs to be discussed quantitatively. *with regards to nucleophilic substitution reactions, electron-withdrawing groups are susceptible to attack by weak nucleophiles. For example, compared to chlorobenzene, chlorodinitrobenzene is susceptible to reactions that displace chloride.{{cite journal , author=J. F. Bunnett, R. M. Conner, doi=10.15227/orgsyn.040.0034, title=2,4-Dinitroiodobe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrophilic Aromatic Substitution
Electrophilic aromatic substitution is an organic reaction in which an atom that is attached to an aromatic system (usually hydrogen) is replaced by an electrophile. Some of the most important electrophilic aromatic substitutions are aromatic nitration, aromatic halogenation, aromatic sulfonation, and alkylation and acylation Friedel–Crafts reaction. Illustrative reactions The most widely practised example of this reaction is the ethylation of benzene. :: Approximately 24,700,000 tons were produced in 1999. (After dehydrogenation and polymerization, the commodity plastic polystyrene is produced.) In this process, acids are used as catalyst to generate the incipient carbocation. Many other electrophilic reactions of benzene are conducted, although on a much smaller scale; they are valuable routes to key intermediates. The nitration of benzene is achieved via the action of the nitronium ion as the electrophile. The sulfonation with fuming sulfuric acid gives benzenesulfonic ac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arene Substitution Patterns
Arene substitution patterns are part of organic chemistry IUPAC nomenclature and pinpoint the position of substituents other than hydrogen in relation to each other on an aromatic hydrocarbon. ''Ortho'', ''meta'', and ''para'' substitution * In ''ortho''-substitution, two substituents occupy positions next to each other, which may be numbered 1 and 2. In the diagram, these positions are marked R and ''ortho''. * In ''meta''-substitution the substituents occupy positions 1 and 3 (corresponding to R and ''meta'' in the diagram). * In ''para''-substitution, the substituents occupy the opposite ends (positions 1 and 4, corresponding to R and ''para'' in the diagram). The toluidines serve as an example for these three types of substitution. Synthesis Electron donating groups, for example amino, hydroxyl, alkyl, and phenyl groups tend to be ''ortho''/''para''-directors, and electron withdrawing groups such as nitro, nitrile, and ketone groups, tend to be ''meta''-directors. Propert ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pure Appl
Pure may refer to: Computing * A pure function * A pure virtual function * PureSystems, a family of computer systems introduced by IBM in 2012 * Pure Software, a company founded in 1991 by Reed Hastings to support the Purify tool * Pure-FTPd, FTP server software * Pure (programming language), functional programming language based on term rewriting * Pure Storage, a company that makes datacenter storage solutions * Pure (CRIS), a research information system bought by Elsevier. Companies and products * Pure (app), dating app * Pure (restaurant chain), a British fast food chain * Pure Insurance, Privilege Underwriters Reciprocal Exchange * Pure Trading, a Canadian electronic communication network operated by CNQ * Pure Digital, a UK consumer electronics company specialising in DAB radios * Pure Oil, a U.S. chain of gas stations * Propulsion Universelle et Récuperation d'Énergie (PURE), a motorsport engineering company * Pure FM (Portsmouth), a university radio station based in P ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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. Aromatic rings are usually nucleophilic, but some aromatic compounds do undergo nucleophilic substitution. Just as normally nucleophilic alkenes can be made to undergo conjugate substitution if they carry electron-withdrawing substituents, so normally nucleophilic aromatic rings also become electrophilic if they have the right substituents.This reaction differs from a common SN2 reaction, because it happens at a trigonal carbon atom (sp2 hybridization). The mechanism of SN2 reaction does not occur due to steric hindrance of the benzene ring. In order to attack the C atom, the nucleophile must approach in line with the C-LG (leaving group) bond from the back, where the benzene ring lies. It follows the general rule for which SN2 reactions occur only at a tetrahedral carbon atom. The SN1 mechanism is p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jerzy Winiarski
Jerzy is the Polish version of the masculine given name George. The most common nickname for Jerzy is Jurek (), which may also be used as an official first name. Occasionally the nickname Jerzyk may be used, which means "swift" in Polish. People *Jerzy, ''nom de guerre'' of Ryszard Białous, Polish World War II resistance fighter * Jerzy Andrzejewski, Polish writer * Jerzy Bartmiński, Polish linguist and ethnologist * Jerzy Braun (other), several people * Jerzy Brzęczek, Polish footballer and manager * Jerzy Buzek, Polish politician and former Prime Minister * Jerzy Dudek, Polish footballer * Jerzy Fedorowicz, Polish actor and theatre director * Jerzy Ficowski, Polish poet and translator * Jerzy Grotowski, Polish theatre director and theorist * Jerzy Hoffman, Polish film director, screenwriter, and producer * Jerzy Jarniewicz, Polish poet, literary critic, translator and essayist * Jerzy Janowicz, Polish tennis player * Jerzy Jurka, Polish-American computational and m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mieczysław Mąkosza
Mieczysław Józef Mąkosza (born 16 November 1934) is a Polish chemist specializing in organic synthesis and investigation of organic mechanisms. Along with Jerzy Winiarski he is credited for the discovery of the aromatic vicarious nucleophilic substitution, VNS. He also contributed to the discovery of phase transfer catalysis reactions. From 1979 to 2005 he was director of the Institute of Organic Chemistry of the Polish Academy of Sciences The Polish Academy of Sciences ( pl, Polska Akademia Nauk, PAN) is a Polish state-sponsored institution of higher learning. Headquartered in Warsaw, it is responsible for spearheading the development of science across the country by a society of .... References 1934 births Polish chemists Living people Recipients of the State Award Badge (Poland) {{Poland-scientist-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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