The activated complex position on the reaction coordinate and the problem of curvature-linearity of the Bronsted relation

Abstract

Abstract A nonequilibrium model of the proton-transfer reaction in a polyatomic system, in which the proton tunneling is associated with the potential of three-center reaction zone AHB (A H plus H B bonds), is proposed. The rate constant calculation is performed within the framework of the Marcus model and uses the intramolecular reorganization (IMR) method for ab initio calculation of the potential energy of the system. Mayer’s program APOST is used for to calculate the one- and two-atom components of the molecule energy (6-31G∗∗ basis set) for the subsystem AHB. The model is used for the quantitative analysis of the interrelated issues of the activated complex position on the reaction coordinate and the curvature – linearity of the Bronsted relation. The discussion is exemplified by a series of gas-phase deprotonation reactions on substituted toluene (substituents: OH, CH3, H, Cl, NC and CN) by the CH2CN− anion. Compared with the standard calculations within the Marcus model, the results predicted a decrease in the variation in the position of the activated complex within the reaction series and consequently a substantial reduction of the Bronsted plot curvature.