Evolution of the Molecular Face during the Reaction Process of F-+CH3Cl→CH3F+Cl-

Bimolecular nucleophilic substitution (S(N)2) reactions are among the fundamental organic reactions, in which electron transfer from the nucleophilic group to the leaving group plays an essential role. We use a high-level ab initio CCSD(T)/aug-cc-pVDZ method in conjunction with our previously-developed molecular face (MF) theory, to investigate the S(N)2 reaction F-+CH3Cl -> CH3F + Cl-. Dynamic representations of molecular shape evolution and electron transfer features throughout the reaction are vividly presented. It is found that along the intrinsic reaction coordinate (IRC), from the beginning of the reaction to the prereaction complex, the molecular intrinsic characteristic contour (MICC) of the nucleophile (F-) contracts slowly, while the electron density on the MICC increases slowly. The MICC of F then expands quickly, and the electron density decreases sharply, especially from the transition state to the product complex. However, for the leaving group (Cl), the MICC contracts, and the electron density increases all along the reaction. Investigations of the potential acting on an electron in a molecule (PAEM) show that, as the reaction progresses, the PAEM gradually decreases between fluorine and carbon, while it gradually increases between carbon and chlorine. This study enhances our understanding of the dynamic processes of bond-forming between F and C atoms and bond-breaking between C and Cl atoms.