Mechanistic studies on Aminolysis of Carbon System

초록

Experimentally, the nucleophilic substitution to the carbon centre could proceed through two different mechanisms1: concerted or stepwise. Our present study focuses on the mutual interaction of the substituents in the nucleophile and substrate ? cross interaction constant ρXY. Experimentally, concerted single step substitution reaction shows a small negative ρXY value.2 In this work (Scheme 1), the reaction mechanism on pyridinolysis of phenyl carbonyl isothiocyanates is investigated using the CPCM approach in gas and acetonitrile continuum polarized model at the B3LYP/6-311+G(d,p) level of theory. We optimized all the reactant complexes, transition states, and product complexes to construct the potential energy surfaces (PES) for six different substituents. Frequency calculations were performed to confirm the stationary species and to provide thermodynamic properties. The concerted single step reaction mechanism is discussed in terms of Hammett constants (ρX, ρY, ?X and cross interaction constant (CIC)3 ρXY). To interpret and confirm the reaction mechanism, orbital interactions and the stereoelectronic effect between the nucleophile and the substrate were also considered along with the respective physical parameters.