Reactivity indices profile: a companion tool of the potential energy surface for the analysis of reaction mechanisms. Nucleophilic aromatic substitution reactions as test case

J Org Chem. 2013 Feb 1;78(3):1091-7. doi: 10.1021/jo3025048. Epub 2013 Jan 11.

Abstract

We herein report on the usefulness of the reactivity indices profiles along a reaction coordinate. The model is tested to fully describe the reaction mechanism of the title reactions. Group nucleophilicity and electrophilicity profiles help describe the bond-breaking/bond-formation processes and the intramolecular electron density reorganization. The reactivity indices' profile analysis is consistently complemented with hydrogen bonding (HB) effects along the reaction coordinate: the final outcome of the reaction is determined by the stage at which the HB complex can be formed. Transition-state structures located for six reactions studied, including the charged nucleophile thiocyanate, show that the main stabilizing interaction is that formed between the hydrogen atom of the nucleophile and the o-NO(2) group. This result discards the role of HB interaction between the nucleophile and the leaving group previously proposed in the literature.