Møller-Plesset MP2/6-31G method was used to examine the gas-phase elimination of 2-substituted alkyl ethyl N,N-dimethylcarbamates. The results of these calculations support a concerted non-synchronous six-membered cyclic transition state mechanism for carbamates containing a Cβ-H bond at the alkyl side of the ester. These substrates produce the N,N-dimethylcarbamic acid and the corresponding olefin. The unstable intermediate, N,N-dimethylcarbamic acid, rapidly decomposes through a four-membered cyclic transition state to dimethylamine and CO2 gas. Correlation of the logarithm of theoretical rate coefficients against original Taft's σ* values gave an approximate straight line (ρ*=-1.39, r=0.9558 at 360°C). In addition to this fact, when log krel is plotted against the theoretical log krel for 2-substituted ethyl N,N-dimethylcarbamates a reasonable straight line (r=0.9919 at 360°C) is obtained, suggesting similar mechanism.
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- 2-substituted alkyl ethyl N
- Gas-phase elimination
- MP2 calculations
- Substituent effects