Ab initio molecular dynamics investigations on the SN2 reactions of OH− with NH2F and NH2Cl

The bimolecular nucleophilic substitution (SN2) reactions of hydroxide anion (OH−) with fluoroamine (NH2F) and chloramine (NH2Cl) have been investigated with ab initio molecular dynamics simulations. For the SN2 reaction of OH− with NH2F, there are two main dynamic reaction pathways after passing the [HO···NH2···F]− barrier. The first one is that the [HO···NH2···F]− transition state directly dissociates to the products of F− and NH2OH without involving any dynamic intermediate complex, and on the contrary, the other one involves the dynamic hydrogen bond F−···H−NH−OH and/or F−···H−O−NH2 intermediate complexes. As to the SN2 reaction of OH− with NH2Cl, there is only one dominant dynamic reaction pathway, which leads to the products of Cl− and NH2OH directly. According to our calculations, the statistical theories including the Rice–Ramsperger–Kassel–Marcus (RRKM) theory and transition state (TS) theory cannot be utilized to model the reaction kinetics for these two SN2 reactions.