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 (SN2) and elimination (E2). The SN2 pathway was further classified into oxygen-side attack (ret-SN2) and backside attack (inv-SN2) based on the nucleophilic approach direction. The calculated results demonstrate that the transition state barriers follow the order inv-SN2 < ret-SN2 < 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 SN2 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.