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PM3 study of the effects of -methylation on the gas-phase kinetics of thermal decomposition of ethyl acetates

I.A.Adejoro

The effects of -methylation on the gas-phase reaction kinetics andmechanism of the pyrolysis of ethyl acetates was studied theoretically at semiempirical PM3 level.All the calculations showed that the thermal decomposition of these alkyl acetates is a concerted asynchronous process via a six-membered cyclic transition state. The overall result of the calculations shows that -methyl substitution has a steric releasing effect in the transition state, hence it is rate enhancing. Also it is found that rate enhancement due to C4-O1 bond stretching in the formation of the T.S. is more significant as a rate determinant than the acidic nature of the  hydrogen eliminated. The first order rate coefficients and computed activation parameters predicted by PM3 method are in good agreement with the experimental results for the series studied.