Theoretical studies on the gas-phase elimination kinetics of 2-arylethyl N,N-dimethylcarbamates [(CH₃)₂NCOOCH₂CH₂Z, Z = 4-CH₃C₆H₄, 4-CH₃OC₆H₄, 4-NO₂C₆H₄]

The gas-phase elimination kinetics of 2-arylethyl N,N-dimethylcarbamates, (CH₃)₂NCOOCH₂CH₂Ar, has been studied at the ab initio MP2/6-31G and MPW1PW91/6-31G(d,p) levels of theory. These carbamates produce N,N-dimethylcarbamic acid and the corresponding 4-substituted styrene in a rate determining step. The unstable intermediate N,N-dimethylcarbamic acid rapidly decarboxylate through a four-membered cyclic transition state to give dimethylamine . These calculations imply a concerted, non-synchronous six-membered cyclic transition state type of mechanism. The present results support the fact that the acidity of the benzylic hydrogen as an important factor for faster elimination rates.