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Ketene Cycloaddition
Ketene cycloadditions are the reactions of the pi system of ketenes with unsaturated compounds to provide four-membered or larger rings. +2 +2 and +2variants of the reaction are known. Introduction Ketenes may react with unsaturated compounds to afford four-membered or larger rings. The first example of this phenomenon was observed in 1908, and since then, cycloadditions of ketenes have expanded and gained synthetic utility. Examples exist of +2 +2 and +2cycloaddition, and conjugated ketenes may act as 4π partners in +2cycloadditions as well. The unique transition state geometry of +2ketene cycloadditions has important stereochemical consequences (see below). Mechanism and Stereochemistry Prevailing Mechanism Ketene cycloadditions proceed by a concerted, +2cycloaddition mechanism. Ketenes, unlike most alkenes, can align antarafacially with respect to other alkenes. Thus, the suprafacial- antarafacial geometry required for concerted, thermal +2cycloaddition can be achie ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ketene
In organic chemistry, a ketene is an organic compound of the form , where R and R' are two arbitrary monovalent chemical groups (or two separate substitution sites in the same molecule). The name may also refer to the specific compound ethenone , the simplest ketene. Although they are highly useful, most ketenes are unstable. When used as reagents in a chemical procedure, they are typically generated when needed, and consumed as soon as (or while) they are produced. History Ketenes were first studied as a class by Hermann Staudinger before 1905. Ketenes were systematically investigated by Hermann Staudinger in 1905 in the form of diphenylketene (conversion of \alpha-chlorodiphenyl acetyl chloride with zinc). Staudinger was inspired by the first examples of reactive organic intermediates and stable radicals discovered by Moses Gomberg in 1900 (compounds with triphenylmethyl group). Properties Ketenes are highly electrophilic at the carbon atom bonded with the heteroatom, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antarafacial And Suprafacial
Antarafacial (Woodward–Hoffmann rules, Woodward-Hoffmann symbol a) and suprafacial (s) are two topology, topological concepts in organic chemistry describing the relationship between two simultaneous chemical bond making and/or bond breaking processes in or around a reaction center. The reaction center can be a p-orbital, p- or Hybrid orbital, sp''n-''orbital (Woodward-Hoffmann symbol ω), a conjugated system (π) or even a sigma bond (σ). * The relationship is ''antarafacial'' when opposite faces of the π system or isolated orbital are involved in the process (think ''anti''). For a σ bond, it corresponds to involvement of one "interior" lobe and one "exterior" lobe of the bond. * The relationship is ''suprafacial'' when the same face of the π system or isolated orbital are involved in the process (think ''syn''). For a σ bond, it corresponds to involvement of two "interior" lobes or two "exterior" lobes of the bond. The components of all pericyclic reactions, including sig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
André Dreiding
André S. Dreiding (22 June 1919 in Zürich – 24 December 2013 in Herrliberg near Zurich) was a Swiss chemist.40 years, many researchers and departments still maintain and use their collections. In order to ease the general supply problem for spare parts or entire models, the 'Dreiding Model Exchange'' was established in 2010 at the University of Illinois at Chicago. References {{DEFAULTSORT:Dreiding, Andre Swiss chemists Columbia University alumni University of Michigan alumni Wayne State University faculty Academic staff of the University of Zurich 1919 births 2013 deaths ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
