Mechanism and dynamics of [formula omitted] + CCl4 halophilic reaction

Abstract

In halophilic reactions, the nucleophile attacks the halogen moiety of the substrate instead of the carbon atom and displaces a carbanion as the leaving group. We report here a detailed ab initio and DFT study of the mechanism and dynamics of the reaction between CCl4 and CH2NO2− in the gas phase. The potential energy profiles for the reaction were mapped using DFT, MP2, and CCSD(T) methods considering the bimolecular halophilic (SN2X), SN2, and H/Cl exchange pathways. The SN2X pathway results in the products CCl3− + CH2ClNO2, while the H/Cl exchange pathway gives CHCl3 + CHClNO2−. The H/Cl exchange products were also possible by a sequential pathway that involved the SN2X reaction followed by a proton transfer from CH2ClNO2 to CCl3−. The SN2X and the sequential H/Cl exchange pathways were found to be barrierless and energetically feasible. The atomic-level mechanisms followed in the reaction was investigated by on-the-fly classical trajectory simulations at the B3LYP/6-311++G∗∗ level of theory. The trajectory simulations support the formation of both the halophilic and H/Cl exchange products. The halophilic reaction was found to largely follow non-IRC dynamical pathway that avoids the pre-transition state complex. In addition, the dynamics of the reaction was found to be nonstatistical with the trajectories showing recrossing behavior and nonexponential lifetimes for the post-transition state complex that leads to the halophilic products.