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A kinetic study of the ethyl radical with allyl compounds Troughton, Gary Ellis

Abstract

The reactions of the ethyl radical with a series of allyl compounds were examined experimentally in the gas phase, and the results were seen to conform to a general mechanism. Specifically, the ethyl radical can abstract a hydrogen atom from the allyl compound, or add to the olefinic linkage of the allyl compound. Dismutation reactions of the product radicals formed in the addition or abstraction reactions were also observed in this study. The metathesis reactions of some allyl compounds were too slow to be measured unless the functional group was deuterated. When this was done in the case of allyl alcohol and allyl formate, primary isotope effects in metathesis could be measured, and were in good agreement with the values predicted on the basis of zero point energy differences. The activation energies of the dismutation reactions of the adduct radicals ranged from 15 to 27 Kcal/mole and were found to depend on the estimated enthalpies of this reaction. In certain cases, a choice between two different reaction routes of the dismutation reaction could be made by comparing the activation energy with the estimated enthalpy change. The dismutation reaction offers a convenient method for the generation of free radicals at low temperatures. In this way, the allyl and ethoxy radicals were generated, and their disproportionation-combination ratios with the ethyl radical were measured. The kinetics of interaction of the ethyl radical with an allyl compound in the gas phase can be compared with the polymerization of that monomer in the liquid phase. Specifically the ratio of the addition rate constant to the metathesis rate constant in the gas phase can be related to the degree of polymerization and a linear relationship between these quantities was found in this study.

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