Density functional theory calculations of the gas-phase elimination kinetics of 2-(dimethylamino)ethyl chloride and ethyl chloride

The kinetic and mechanism of the unimolecular gas-phase elimination of 2-(dimethylamino)ethyl chloride were examined by using density functional theory methods to explain the enhanced reactivity in gas-phase elimination compared to the parent compound ethyl chloride. The plausible anchimeric assistance of the dimethylamino proposed in the literature was investigated. The theoretical calculations were carried out at B3LYP/6-31G(d,p), B3LYP/6-31++G(d,p), MPW1PW91/6-31G(d,p), MPW1PW91/6-31++G(d,p), PBEPBE/6-31G(d,p), and PBEPBE/6-31++G(d,p) levels of theory. The previous proposed reaction path of anchimeric assistance has an energy of activation 60 kJ/mol higher than the experimental value. The located transition state in the minimum energy path is a four-centered cyclic configuration comprising chlorine, hydrogen and two carbon atoms. Calculation results give a lower energy of activation of 2-(dimethylamino)ethyl chloride when compared to the parent compound ethyl chloride. This result is due to the stabilization of the transition state because of electron delocalization involving the dimethylamino substituent.