Gas phase reactions of nitromethyl carbanion with CHCl3 and CCl4: A theoretical investigation

The ion/molecule reactions of CH2NO2- with CCl4 and CHCl3 in gas phase have been theoretically investigated using BH&HLYP, B3LYP and MP2 methods with 6-31+G∗ and 6-311+G∗∗ basis sets. The experimentally observed H/Cl exchange reaction between CH2NO2- and CCl4 was found to include two individual reactions, the chlorine cation transferring from CCl4 to CH2NO2- via a chlorine-attack transition state and the proton transferring from CH2ClNO2 to CCl3- via a proton-attack transition state. The calculated energies indicate that the H/Cl exchange is both kinetically and thermodynamically favorable. The H/Cl exchange reaction was found to be also possible for CHCl3, but a notable activation barrier represented by a bridge-like transition state and strong endothermicity for the chlorine cation-transfer step make this reaction impossible under low-energy condition. The classic SN2 reactions between CH2NO2- and the two chloromethanes were also calculated and notable energy barriers were identified for them.