Activation Strain Analyses of Counterion and Solvent Effects on the Ion-Pair SN2 Reaction of NH2− and CH3Cl

We have computationally studied the bimolecular nucleophilic substitution (SN2) reactions of MnNH2 (n−1) + CH3Cl (M+ = Li+, Na+, K+, and MgCl+; n = 0, 1) in the gas phase and in tetrahydrofuran solution at OLYP/6-31++G(d,p) using polarizable continuum model implicit solvation. We wish to explore and understand the effect of the metal counterion M+ and of solvation on the reaction profile and the stereochemical preference, that is, backside (SN2-b) versus frontside attack (SN2-f). The results were compared to the corresponding ion-pair SN2 reactions involving F− and OH− nucleophiles. Our analyses with an extended activation strain model of chemical reactivity uncover and explain various trends in SN2 reactivity along the nucleophiles F−, OH−, and (Formula presented.), including solvent and counterion effects.