The gas-phase elimination of ethyl N,N-dimethylcarbamates substituted with electron-withdrawing groups at the 2-position of the ethyl were studied by using the Møller-Plesset MP2/6-31G method. Calculations suggest a concerted non-synchronous six-membered cyclic transition state type of mechanism of the above-mentioned carbamates. These substrates undergo thermal elimination to produce the N,N-dimethylcarbamic acid and the corresponding substituted olefin in the rate-determining step. The unstable intermediate, N,N-dimethylcarbamic acid rapidly decomposes through a four-membered cyclic transition state to dimethylamine and CO2 gas. The logarithm of relative theoretical rate coefficients when plotted against original Taft's σ* values gave an approximate straight line (ρ*=-0.137±0.023, r=0.9610 at 360 °C). In addition to this fact, plotting experimental log krel. against the theoretical log krel. for 2-substituted ethyl N,N-dimethylcarbamates an approximate straight line (r=0.9578 at 360 °C) is obtained, which means similar mechanism.
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- 2-Substituted electron withdrawing groups
- Ethyl N,N-dimethylcarbamates
- Gas-phase elimination
- MP2 calculations
- Substituent effects