Quantum chemical studies of azoles 10. Transition states in the routes of electrophilic substitution in 1H-tetrazole via the elimination—addition mechanism without preliminary formation of N-protonated azolium salts

Abstract

The results of theoretical search for model transition states of electrophilic substitution in 1H-tetrazole (1) without preceding formation of N-protonated azolium salts are presented. Two routes of the reaction were proposed: A, attack of molecule 1 by the nucleophile HO^–(aq)) to form the anion to which the electrophile H₃O⁺(aq)) is added further; and B, attack of molecule 1 by the same electrophile with the subsequent addition of the same nucleophile to the specifically solvated protonated species. The thermodynamic parameters were calculated earlier at the indicated routes. In this article, the kinetic characteristics of the reactions were estimated by the DFT/B3LYP/6-31G(d) method using the scanning pro-cedure of the potential energy surface. Both steps of route A turned out to be barrier-less, while in route B only its first step is barrier-less and the second step is conjugated with surmounting an activation barrier of ~35 kcal mol^–1 between the formed prereaction complex and the products of electrophilic substitution.