Theoretical Studies on the Bimolecular Nucleophilic Substitution Reactions for Y-substituted Phenoxy Hydrogen Isothiocyanophosphonate

초록

The kinetics and mechanism of the pyridinolysis (XC5H4N) of phenoxy hydrogen isothiocyanophosphonate (Y-C6H4O(P=O)(H)NCS) in acetonitrile are investigated at room temperature 25.0oC. Physical and thermodynamic parameters as well as molecular orbital overlapping indicate the back-side nucleophilic attack of pyridines and leaving group (?NCS) departure strategies. 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. In addition, the steric effects of the ligands can play an important role in determining the rates of the reactions.