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  • 1970-1974  (2)
  • 1960-1964  (2)
  • 1955-1959
  • 1930-1934
  • 1890-1899
  • 1972  (2)
  • 1964  (2)
  • 1930
  • Free radicals
  • 1
    Electronic Resource
    Electronic Resource
    The Electronic Properties of Diradicals (1972)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 11 (1972), S. 92-111 
    Details
    ISSN: 0570-0833
    Keywords: Diradicals ; Free radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A review of the various possible definitions of diradicals leads the authors to describe these systems as having two odd electrons in degenerate or nearly-degenerate molecular orbitals. A study of the wave-function for the two odd electrons shows that its form depends entirely on whether the diradical is homo- or heterosymmetric. Energy schemes are given in these two cases, as well as in the intermediate “non-symmetric” case. The extent of zwitterionic character in diradical states is also investigated. This is followed by a discussion of intersystem crossing between singlet and triplet diradical states via spin-orbit coupling and other mechanisms. The electronic matrix elements for spin-orbit coupling are calculated and evaluated numerically for various model cases. It is then possible to establish general rules for favorable (electronic) intersystem crossing. In 1,3 or 1,4 diradicals its efficiency is estimated to be comparable with that in aromatics. The role of the electron-nuclear hyperfine interaction in mixing singlet and triplet states, particularly in CIDNP, is explained.Finally the question of whether diradicals actually occur as secondary minima on potential energy surfaces is examined. Recent quantum-mechanical calculations, in contradiction to some thermochemical and kinetic evidence, lead to flat singlet surfaces without significant minima.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.197200921
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Organic Syntheses via Free-Radical Displacement Reactions of OrganoboranesBased in part on Chapter XIX of a forthcoming book (Baker Lectures) by H. C. Brown: Boranes in Organic Chemistry. Cornell University Press. Ithaca. N.Y. (USA) (1972)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 11 (1972), S. 692-700 
    Details
    ISSN: 0570-0833
    Keywords: Radical reactions ; Displacement reactions ; Organoboranes ; Free radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the few short years since the discovery that organoboranes undergo facile free-radical substitution, application of these reactions has become a major new area of synthetic utility. Organoboranes undergo a wide variety of free-radical reactions such as autoxidation to the alcohol or hydroperoxide, 1, 4 addition to α,β-unsaturated derivatives, addition to disulfides, and oxygen-induced radical coupling. It is evident that organoboranes constitute a versatile new source of free radicals and that these reactions can be readily controlled to give very clean syntheses. The application of these reactions will be discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.197206921
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Intramolecular Free-Radical Reactions (1964)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 525-538 
    Details
    ISSN: 0570-0833
    Keywords: Radical reactions ; Free radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the present article an attempt is made to summarize the steric requirements and the influence of neighboring groups which determine the course of intramolecular radical reactions. Steroids are used as substrates for these reactions, since here the spatial arrangement of the ring members and the distances between substituents are largely fixed. Furthermore, intramolecular free-radical reactions are of practical importance in steroid chemistry in connection with substitution at non-activated carbon atoms. Almost all the reactions discussed begin with the formation of an oxygen radical by oxidation of an alcohol with lead tetraacetate or by homolysis of the corresponding hypoiodite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196405251
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Free Radicals and Free-Radical Reactions of Monovalent and Divalent SulfurFree-radical reactions of tetra- and hexavalent sulfur are not considered in this work. For a survey of these reactions, see [16], p. 326. (1964)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 602-608 
    Details
    ISSN: 0570-0833
    Keywords: Free radicals ; Radical reactions ; Sulfur ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organic free radicals of monovalent sulfur have not been hitherto observed in solution or in melts. Steric hindrance and resonance stabilization, which are responsible for the stability of the triarylmethyl, diphenylnitrogen, and phenoxyl radicals, are apparently insufficient to stabilize the organic free radicals of monovalent sulfur in such concentrations that they can be detected by current physical methods. - It was only in 1963 that aminopolysulfur radicals (R2N—Sn—S·) were detected in solution, and arylsulfur radicals (Ar-S·) and phenylselenium radicals were isolated at ca. -180°C. - Organically bound sulfur can be stabilized in the free-radical state if association of the radicals is prevented by fixing in a crystal lattice (“cystine radical”), by repulsion between radical ions (sulfinium salts), or by freezing-in (arylsulfur radicals).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196406021
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    Paper (German National Licenses)
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