Reaction mechanism of an intracluster SN2 reaction induced by electron capture

Abstract

Bimolecular nucleophilic substitution (S_N2) reactions have been widely investigated from both experimental and theoretical points of view because they represent one of the simplest organic reactions. Most studies on S_N2 reactions have been focused on bimolecular collision. In contrast, information on intracluster S_N2 reactions is limited. In this study, an intracluster S_N2 reaction of NF₃–CH₃Cl triggered by electron attachment was investigated using a direct ab initio molecular dynamics (AIMD) method. In the structure of NF₃–CH₃Cl, the N–F bond in NF₃ is oriented collinearly toward the carbon atom of CH₃Cl. After electron capture by NF₃–CH₃Cl, the F⁻ ion that is generated from the (NF₃)⁻ moiety collides with the carbon atom of CH₃Cl. The intracluster S_N2 reaction occurs as follows: (NF₃–CH₃Cl)⁻ (electron capture state) → NF₂–(F⁻)–CH₃Cl (pre-reaction complex) → transition state (TS) → NF₂–CH₃F–Cl⁻ (post-reaction complex) → NF₂ + CH₃F + Cl⁻ (product state). The reaction energy is efficiently transferred to the translational mode of Cl⁻, and the Cl⁻ ion with a high translational energy is then removed from the system. This energy is significantly larger than that of Cl⁻ formed in the bimolecular S_N2 reaction (F⁻ + CH₃Cl). The reaction mechanism is discussed based on the theoretical results.