Theoretical Study of Nucleophilic Identity Substitution Reactions at Nitrogen, Silicon and Phosphorus versus Carbon: Reaction Pathways, Energy Barrier, Inversion and Retention Mechanisms

Gas-phase identity S(N)2(N), S(N)2(Si) and S(N)2(P) versus S(N)2(C) reactions with Cl- are investigated by the ab initio method. Front-side attack identity S(N)2 reactions considered have all double-well potential energy surfaces (PES), and back-side attack identity S(N)2(C) and S(N)2(N) reactions have also double-well PES, while back-side attack identity S(N)2(Si) and S(N)2(P) have single-well PES. In addition, the geometrical transformations, potential energy profiles of front-side and back-side attack identity S(N)2(N), S(N)2(Si) and S(N)2(P) versus S(N)2(C) reactions based on the IRC calculations are described, the differences between them for the front-side or back-side attack reactions have been demonstrated.