Theoretical Studies on OH−+NH2Cl Reaction: Nucleophilic Substitution at Neutral Nitrogen

Abstract

The S_N2 and proton transfer (PT) pathways for ${\mathrm{\text{OH}}}^{-}+{\mathrm{\text{NH}}}_2$Cl reaction are represented by employing various electronic structure computations. Both back-side S_N2 and PT channels are exothermic and stationary points of PESs are below the reactant asymptote. Overall, the PES is similar to the C-centered S_N2 reactions. Conversely, ion-dipole complex was not found for ${\mathrm{\text{OH}}}^{-}+{\mathrm{\text{NH}}}_2$Cl system. The N–HOH/NH–Cl hydrogen bond characterizes on either side of the reaction barrier of nitrogen complexes. Moreover, a halogen-bonded complex (HO⁻–ClNH₂) and two types of H-bond complexes (HONH₂–Cl⁻ and Cl⁻–HONH₂) were described, predicting an important role in dynamics. The PT pathway may be the major channel in the title system, which is contradictory to ${\mathrm{\text{OH}}}^{-}+{\mathrm{\text{CH}}}_3$Cl and ${\mathrm{\text{F}}}^{-}+{\mathrm{\text{NH}}}_2$Cl reactions. Here, MP2, B3LYP and CAM-B3LYP methods show overall excellent consistency with CCSD(T)/CBS energies and are recommended to carry out dynamics simulations.