Computational comparison of reactions of CS2 with CHX•- (X = F, Cl, and Br): Do F, Cl, and Br substitutions effect differently?

Abstract

Calculations based on density functional theory (DFT) have been carried out for the gas-phase ion-molecule reactions of CS 2 with CHX •- ( X = F , Cl , and Br ) to investigate the effect of the halogen-substituent on the reaction mechanism. The doublet potential energy surfaces (PESs), involving two striking reaction patterns named by the middle-C attack and the end-S attack in terms of anion attack on the C and S atoms of CS 2, have been explored and characterized in detail. Compared with the results of the end-S attack, reaction with the middle-C attack pattern displays more efficiency on PES. For a given reaction pattern, the reactions of CHCl •- and CHBr •- occur with similar efficiencies and reactivity trends. The CHF •- anion displays remarkably different reactivity, which is traced to its lower electron binding energy and the effect of the electronegative fluorine substituent. This is in good agreement with the experimental observation. According to the property of the product branching ratios in experiment, dynamical effect is used to evaluate the reason that the end-S attack with less energetically favorable obtained in our theoretical studies is comparable to the middle-C attack.