Ab initio and DFT calculations of benzaldoxime elimination kinetics in the gas phase

The mechanism for the gas-phase molecular elimination kinetics of benzaldoxime was examined at MP2/6-31G, MP2/6-31G(d,p), B3LYP/6-31G, B3LYP/6-31G(d,p), MPW1PW91/6-31G, and MPW1PW91/6-31G(d,p) levels of theory. The products of elimination of this oxime are benzonitrile and water. Calculated thermodynamic and kinetic parameters estimated from B3LYP/6-31G was found to be in better agreement with the experimental values. Transition state structure is best described as a four-membered cyclic structure with good approximation to planarity. NBO charges analysis revealed a little greater polarization of the benzylic C^δ - H^δ+ rather than N ^δ - OH^δ-. Bond indexes and synchronicity parameters are in agreement with a concerted semi-polar type of mechanism with benzylic C - H bond breaking as determining step of the reaction.