Theoretical study of the elimination kinetics of several 2-substituted ethyl N, N-dimethylcarbamates in the gas phase, [(CH 3) 2NCOOCH 2CH 2Z, Z=CH 2Cl, C≡CH, C≡N

Abstract

The theoretical studies of the gas-phase elimination of 2-substituted ethyl N, N-dimethylcarbamates (Z=CH 2Cl, C≡CH, C≡N) were performed using ab initio MP2/6-31G and MP2/6-31G(d) levels of theory. The gas phase elimination reaction of these carbamates yields N, N-dimethylcarbamic acid and the corresponding substituted olefin in a rate-determining step. The intermediate N, N-dimethylcarbamic acid is unstable and rapidly decomposes through a four-membered cyclic transition state to dimethylamine and CO 2 gas. The results of these calculations suggest a mechanism to be concerted, asynchronous, and a six-membered cyclic transition state structure. Plotting the relative theoretical rate coefficients against Taft's σ* values gave an approximate straight line ( ρ*=0.4057, r=0.9894 at 360 °C). The correlation between experimental log k rel vs. theoretical log k rel. for these 2-substituted ethyl N, N-dimethylcarbamates gave an approximate straight line ( r=0.9715 at 360 °C), suggesting the same type of mechanism.