Theoretical Studies on the Bimolecular Nucleophilic Substitution Reactions for Benzene Sulphonates with Pyridines

초록

The kinetics and mechanism of the pyridinolysis (XC5H4N) of isothiocyano benzene sulphonates [(Y-C6H4O)S(=O)2(NCS)] in acetonitrile are investigated computationally at 25.0 oC using Gaussian 09 package in acetonitrile solvent. According to the literature and several experimental evidences, concerted or a stepwise mechanistic route during the expulsion of isothiocyanate (NCS) leaving group from the intermediate or TS are possible, where positive and negative ρX, and βX values imply the characteristics of the nucleophilic attack. Physical and thermodynamic parameters as well as molecular orbital analysis indicate the concerted back-side nucleophilic attack of pyridines and leaving group (?NCS) departure strategies. In addition, the steric effects of the ligands can play an important role in determining the rates of the reactions