Theoretical Study on the Nucleophilic Ring-Opening Reaction between F^- and Oxirane

This work investigated the ring-opening reaction mechanism between F^- and oxirane by combining electronic structure calculations with chemical dynamics simulations. Electronic structure calculations revealed two primary reaction pathways: nucleophilic substitution (S_N2) and elimination (E2). The S_N2 pathway was further classified into oxygen-side attack (ret-S_N2) and backside attack (inv-S_N2) based on the nucleophilic approach direction. The calculated results demonstrate that the transition state barriers follow the order inv-S_N2 < ret-S_N2 < E2 for both gas phase and aqueous phase. Chemical dynamics simulations exhibited distinct collision energy dependence. At a low collision energy (9.2 kcal·mol^-1), the S_N2 pathway dominated due to its lower energy barrier (-5.1 kcal·mol^-1). When the collision energy increased to 43.8 kcal·mol^-1, the E2 elimination channel became accessible, displaying unique nonintrinsic reaction coordinate dynamic characteristics. Notably, a novel CH₂ abstraction pathway was identified, which proceeds via a concerted C-C bond cleavage mechanism and demonstrates significant reactivity with a branching ratio of 0.56 under high collision energy. Activation strain model elucidated the crucial role of strain energy in determining transition state stability. This study provides a deeper mechanistic understanding of nucleophilic reactions involving cyclic compounds and offers theoretical foundations for related experimental investigations.