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 (S(N)2) 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 (S(N)2-b) versus frontside attack (S(N)2-f). The results were compared to the corresponding ion-pair S(N)2 reactions involving F- and OH- nucleophiles. Our analyses with an extended activation strain model of chemical reactivity uncover and explain various trends in S(N)2 reactivity along the nucleophiles F-, OH-, and NH2-, including solvent and counterion effects. (c) 2019 Wiley Periodicals, Inc.