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Encyclopedia > Umpolung

Umpolung or polarity inversion in organic chemistry is the chemical modification of a functional group with the aim the reversal of polarity of that group. This modification allows secondary reactions of this functional group that would otherwise not be possible [1]. The concept was introduced by D. Seebach (hence the German word umpoling for polarity inversion) and E.J. Corey. A classic example of polarity inversion is observed in dithiane chemistry. Organic chemistry is the scientific study of the structure, properties, composition, reactions, and synthesis of organic compounds that by definition contain carbon. ... ... layers]] that separate organs or subcompartments in organisms. ... Elias James Corey (born July 12, 1928) is an American organic chemist. ...


Ordinarily the oxygen atom in the carbonyl group is more electronegative than the carbon atom and therefore the carbonyl group reacts as an electrophile at carbon. This polarity can be reversed when the carbonyl group is converted into a dithiane or a thioacetal. The same carbonyl carbon atom is now more electronegative than two neighboring sulfur atoms and now this carbon is able to react as a nucleophile. In synthon terminology the ordinary carbonyl group is an acyl cation and the dithiane is a masked acyl anion. In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom. ... It has been suggested that this article or section be merged with electronegativity. ... In chemistry, an electrophile (literally electron-lover) is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile. ... An acetyl group that contains a sulfur atom (see thiol) This page is a candidate to be copied to Wiktionary. ... General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Atomic mass 32. ... In chemistry, a nucleophile (literally nucleus lover) is a reagent which is attracted to centres of positive charge. ... A synthon is a concept in retrosynthetic analysis. ... An acyl or acyl group is any radical (or functional group) obtained from an carboxylic acid by the removal of the carboxylic hydroxyl group. ... A cation is an ion with positive charge. ... An acyl or acyl group is any radical (or functional group) obtained from an carboxylic acid by the removal of the carboxylic hydroxyl group. ... An anion is an ion with negative charge. ...


When the dithiane is derived from an aldehyde such as acetaldehyde the acyl proton can be abstracted by n-butyllithium in THF at low temperatures. The thus generated 2-lithio-1,3-dithiane reacts as a nucleophile in nucleophilic displacement with alkyl halides such as benzyl bromide, with other carbonyl compounds such as cyclohexanone or oxiranes such as styrene oxide. After hydrolysis of the dithiane group the final reaction products are α-alkyl-ketones or α-hydroxy-ketones. A common reagent for dithiane hydrolysis is (bis(trifluoroacetoxy)iodo)benzene. An aldehyde is either a functional group consisting of a terminal carbonyl group or a compound containing a terminal carbonyl group. ... R-phrases , , S-phrases , , , Flash point −39 °C Autoignition temperature 185 °C RTECS number AB1925000 Supplementary data page Structure and properties n, εr, etc. ... An organolithium reagent is a carbon nucleophile similar to a Grignard reagent. ... In chemistry, an alkyl halide is an organic molecule of the form R_X, where X is a halide and R contains a carbon atom bonded to other functional groups or hydrogens. ... Benzyl bromide, or α-bromotoluene, is an organic compound consisting of a benzene ring substituted with a bromomethyl group. ... Cyclohexanone is six-carbon cyclic molecule with a ketone functional group. ... Hydrolysis is a chemical process in which a molecule is split into two parts by the addition of a molecule of water. ... (Bis(trifluoroacetoxy)iodo)benzene is a hypervalent iodine compound and a reagent in organic chemistry. ...

Dithiane chemistry

Dithiane chemistry opens the way to many new chemical transformations. One example is found in so-called anion relay chemistry in which an anionic functional group resulting from one organic reaction is transferred to a different location within the same carbon framework and available for secondary reactions [2]. In this example of a multi component reaction both formaldehyde (1) and isopropylaldehyde (8) are converted into dithianes 3 and 9 with propane-1,3-dithiol. Sulfide 3 is first silylated by reaction with tert-butyllithium and then trimethylsilyl chloride 4 and then the second acyl proton is removed and reacted with optically active (-)-epichlorohydrin 6 replacing chlorine. This compound serves as the substrate for reaction with the other dithiane 9 to the oxirane ring opening product 10. Under influence of the string base HMPA, 10 rearranges in a 1,4-Brook rearrangement to the silyl ether 11 reactivating the formaldehyde dithiane group as an anion (hence the anion relay concept). This dithiane group reacts with oxirane 12 to the alcohol 13 and in the final step the sulfide groups are removed with (bis(trifluoroacetoxy)iodo)benzene. The chemical compound formaldehyde (also known as methanal), is a gas with a strong pungent smell. ... An organolithium reagent is any organic compound with a direct bond between a carbon and a lithium atom. ... When polarized light is passed through a substance containing chiral molecules (or nonchiral molecules arranged asymmetrically), the direction of polarization can be changed. ... Hexamethylphosphoramide (abbreviated HMPA) is a clear, colorless liquid with an aromatic odour. ... Silyl ethers are a group of chemical compounds sharing a common functional group in which a silicon atom is covalently bonded to an alkoxy group. ... (Bis(trifluoroacetoxy)iodo)benzene is a hypervalent iodine compound and a reagent in organic chemistry. ...

anion relay chemistry, Ph stands for phenyl


The umpolung concept is also found in the:

The Benzoin condensation is a condensation reaction between two aromatic aldehydes, especially benzaldehyde that is catalyzed by a cyanide. ...

External links

The International Union of Pure and Applied Chemistry (IUPAC) is an international non-governmental organization devoted to the advancement of chemistry. ... The Gold Book or Compendium of Chemical Terminology (ISBN 0865426848) is a book published by IUPAC containing internationally accepted definitions for terms in chemistry. ...

References

  1. ^  Generation and synthetic applications of 2-lithio-1,3-dithianes Dieter Seebach, Elias J. Corey J. Org. Chem.; 1975; 40(2); 231-237. Abstract
  2. ^  Anion Relay Chemistry: An Effective Tactic for Diversity Oriented Synthesis Amos B. Smith, III and Ming Xian J. Am. Chem. Soc.; 2006; 128(1) pp 66 - 67; (Communication) DOI: 10.1021/ja057059w Abstract

  Results from FactBites:
 
Umpolung Information (621 words)
Umpolung or polarity inversion in organic chemistry is the chemical modification of a functional group with the aim of the reversal of polarity of that group.
The concept was introduced by D. Seebach (hence the German word umpolung for polarity inversion) and E.J. Corey.
Classic umpolung applications can be found in Grignard reagents and in the Benzoin condensation.
Umpolung - Wikipedia, the free encyclopedia (619 words)
Umpolung or polarity inversion in organic chemistry is the chemical modification of a functional group with the aim of the reversal of polarity of that group.
The concept was introduced by D. Seebach (hence the German word umpolung for polarity inversion) and E.J. Corey.
Classic umpolung applications can be found in Grignard reagents and in the Benzoin condensation.
  More results at FactBites »

 
 

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