Activation Strain Analyses of Counterion and Solvent Effects on the Ion-Pair S N 2 Reaction of NH 2 - and CH 3 Cl.

We have computationally studied the bimolecular nucleophilic substitution (S _N 2) reactions of M _n NH ₂ ^(n-1) + CH ₃ Cl (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 NH 2 - , including solvent and counterion effects. © 2019 Wiley Periodicals, Inc.
(© 2019 Wiley Periodicals, Inc.)