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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