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  • 1975-1979  (3)
  • 1960-1964  (2)
  • 1920-1924
  • 1890-1899
  • 1979  (3)
  • 1964  (2)
  • Free radicals
  • 1
    Electronic Resource
    Electronic Resource
    Study of an asymmetric ESR signal in X-irradiated human tooth enamel (1979)
    Springer
    Calcified tissue international 29 (1979), S. 95-99 
    Details
    ISSN: 1432-0827
    Keywords: ESR ; Radiation ; Free radicals ; Enamel ; ENDOR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary An asymmetric ESR signal and an outer doublet signal centered atg=2.00 produced in human tooth enamel by X-irradiation have been studied over a temperature range from liquid helium temperature to 380° K. The line shape of the asymmetric signal for an enamel crystallite is Lorentzian at room temperature. The temperature dependence of the integrated intensity of the asymmetric signal suggests that the signal follows a singlet-triplet model with the exchange interaction of 0.022 eV. Below about 60° K the asymmetric signal becomes broad as the temperature is decreased. The ENDOR line of the asymmetric signal shows that there exists interaction between the centers and protons. The temperature dependence of the integrated intensity of the double signal is analogous to that of the asymmetric signal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02408063
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Capto-dative Substituent Effects in Syntheses with Radicals and Radicophiles [New synthetic methods (32)]Capto-dative Substitution Effects, Part 5. - Part 4: [67].Dedicated to the double anniversary: 100 years Wurster's salts and 50 years Paneth's radical reactions with mental mirrors (1979)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 18 (1979), S. 917-932 
    Details
    ISSN: 0570-0833
    Keywords: Donor-acceptor systems ; Substituent effects ; Free radicals ; Radicophiles ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 100 yers old Wurster's salts have long been recognized as compounds with redical cations. Their unusual stabilization derives partly form capto-dative (cd) substitution. This principle is now discussed as one factor of radical stabilization and it is applied to simple methine derivatives. cd-Substitution has synthetically useful applications: cd-substituents on a carbon atom allow its selective dehydrodimerization. Olefines with geminal and thus cross-conjugated cd-substituents are “radicophilic” and permit twofold carbon radical addition. cd-Substituted olefines are useful antioxidants, polymerization inhibitors and are promising agents in the control of biological radical reactions. Generally, many reactions of cd-substituted molecules appear to involve radicals.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.197909171
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Anchimerically Accelerated Bond Homolyses (1979)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 18 (1979), S. 173-180 
    Details
    ISSN: 0570-0833
    Keywords: Homolysis ; Free radicals ; Anchimeric effect ; Neighboring-group effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radical reactions of the type R1—a—b—R2→•a—b—R1 + •R2 are feasible if the new bond formed between b and R1 is considerably stronger than the old bond between a and R1. Furthermore, both the radical fragments formed must be resonance stabilized. An example of this reaction type is the thermolysis of benzyl trimethylsilylmethyl ethers, in which the trimethylsilyl group (with empty orbitals) migrates to the oxygen atom (with lone pairs). Assumption of a cyclic reactive intermediate with pentacoordinated silicon explains the observed intramolecular nature and the negative entropy of activation of such homolyses.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.197901733
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  • 4
    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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  • 5
    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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