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  • 1
    Digitale Medien
    Digitale Medien
    Sauerstoff-Abfang von Radikalen in überkritischem Kohlendioxid; Bildungsenthalpie und Rekombinationsbarriere des Cycloheptatrienyl-Radikals (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1679-1690 
    Details
    ISSN: 0947-3440
    Schlagwort(e): Oxygen trapping ; Radical recombination barrier ; Radical stabilization energy ; Tropenyl-oxygen equilibrium ; Supercritical fluid reactions ; Alkylperoxy bond strengths ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Oxygen Trapping of Radicals in Supercritical Carbon Dioxide; Heat of Formation and Recombination Barrier of the Cycloheptatrienyl RadicalThe homolytic thermal cleavage of bitropenyl (1) in supercritical carbon dioxide has been measured in the presence of 1 to 180 bar oxygen between 120 and 170°C. From these data the activation parameters of the dissociation and recombination reaction are derived, which lead to a heat of formation for the tropenyl radical (2) of ΔHfo = 64.7 kcal · mol-1. By using this value a radical stabilization energy (RSE) or 31.5 kcal · mol-1 is obtained, which differs by 1.7 kcal · mol-1 from the planar, acyclic isomer (trans,trans-1,3,6-trien-5-yl: RSE = 29.8 kcal · mol-1), which is practically equivalent to the relief of ring strain due to the formation of the radical. In agreement with the observed stability of 2 the equilibrium constant for its reaction with oxygen at 143°C is Keq = 727.7 mol-1, which corresponds to a bond strengths of 31.5 kcal · mol-1 for R-O2·. The equipment and the method used for these experiments are described in detail.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jlac.199619961029
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  • 2
    Digitale Medien
    Digitale Medien
    Zur Rekombinationsenthalpie von Radikalen  -  Thermochemie der Ringöffnung von Cyclophanen (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 2141-2154 
    Details
    ISSN: 0947-3440
    Schlagwort(e): Diradicals ; Gasphase kinetics ; Trapping, NO and O2 ; Supercritical fluid reactions ; Reaction forcefield ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Radical Recombination Enthalpy.  -  Thermochemistry of the Ringopening of CyclophanesBy thermolysis of the cyclophanes 1, 5, 8, 11, 14, 18, and 21 in the presence of NO or O2 the enthalpy profiles for the ring opening were determined from the temperature, NO, or O2 dependance of the trapping rates of the intermediate diradicals. The experimental enthalpy wells, which varied between 3 and 12 kcal · mol-1, can be simulated well with a reaction forcefield making use of the EVBH method of Malrieu et al. This result gives confidence that also meaningful recombination barriers of radicals can be obtained by this method.
    Zusätzliches Material: 18 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jlac.199619961229
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