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Kinetic study of the gernation and reactions of allyl and cyclopropyl radicals in the gas phase Kambanis, Stamatis M.

Abstract

Allyl and cyclopropyl radicals were generated in the gas phase at a mean temperature of 140°C by new methods which promise to be of general application. Thus the radical R• may be generated by either of the two sequences: [formulas omitted] The addition-dismutation sequence was used to generate the allyl radical from allyl 3-butenoate and from diallyl oxalate, and the cyclopropyl radical from allyl cyclopropyl-carboxylate and from cyclopropyl 3-butenoate. The meta-thesis-dismutation sequence was tested for the generation of methyl radicals from the methyl ester of cyclohexa-1,4-diene-3-carboxylic acid, and applied to the generation of allyl radicals from the corresponding allyl ester. The Arrhenius parameters of the generating sequence reactions for every system were measured and discussed. These methods generate R• radicals in the presence of an excess of the sensitizing radicals, so that the present systems allow the observation of the patterns of R•/C₂H•₅ interaction. Allyl radicals were generated in the absence of appreciable amounts of other radicals, in the gas phase, by the u n s e n s i t i z e d thermal decomposition: C₃H₅OOCCOOC₃H₅ → 2C₃H•₅ + 2CO₂ log k(sec.⁻¹) = (14 ± 1) - (37 ± 2)10³/2.3RT Allyl radicals were also generated in the presence of an equal amount of cyclohexadienyl radicals in the gas phase by the unsensitized thermal decomposition: [formula omitted] log k(sec.⁻¹) = (14 ± 1) - (38 ± 3)10³/2.3RT The Arrhenius parameters of these two decompositions indicate that all the bonds which are finally broken are significantly extended in the transition state. The combination, disproportionation, isomerization, and metathesis reactions were investigated for the allyl and cyclopropyl radicals. Typical results include: [formulas omitted]

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