Solvent Molecule-Induced Competitive Ion–Molecule Nucleophilic Substitution Reactions Involving an α-Nucleophilic Reagent

High Resolution Image Download MS PowerPoint Slide Under microsolvent conditions, when the α-nucleophile HOO – reacts with CH 3 Br, it can abstract a proton from the solvent CH 3 OH to induce alternative nucleophile CH 3 O – (HOOH). In the present work, the competition between the normal HOO – –S N 2 pathway and the photon transfer (PT)-induced CH 3 O – –S N 2 pathway has been explored by quantum chemistry calculations for HOO – (CH 3 OH) n and CH 3 O – (HOOH) 0,1 (CH 3 OH) n −1 reacting with CH 3 Br. The potential energy profile of the HOO – –S N 2 pathway exhibits that the energy barriers of the traditional back-side attack substitution are 0.4–3.8 kcal/mol lower than those of the CH 3 O – –S N 2 pathway, suggesting the HOO – (CH 3 OH) n is more active, which is consistent with the experimental phenomenon. The activation strain analysis suggests compared to the CH 3 O – –S N 2 pathway, the stronger interaction energy between the HOO – (CH 3 OH) and CH 3 Br over the entire reaction course stabilizes its transition state, which is caused by the stronger orbital interaction of the HOO – –S N 2 pathway. The barrier heights of both pathways are increased with the incremental hydration, but the PT-induced CH 3 O – –S N 2 pathway is highly suppressed. The enhanced reactivity of reactions involving HOO – (CH 3 OH) n is found through comparison with CH 3 O – (HOOH) 0,1 (CH 3 OH) n −1 nucleophiles and is ascribed to the α-nucleophilic character of the HOO – anion. This work deepens an understanding of the nature of the α-effect nucleophile and highlights the effect of the solvent molecule on the enhanced reactivity.