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.