Activation Strain Analyses of Counterion and Solvent Effects on the Ion-Pair SN 2 Reaction of NH 2 - and CH3 Cl.

We have computationally studied the bimolecular nucleophilic substitution (SN 2) reactions of Mn NH2 (n-1) + CH3 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 (SN 2-b) versus frontside attack (SN 2-f). The results were compared to the corresponding ion-pair SN 2 reactions involving F- and OH- nucleophiles. Our analyses with an extended activation strain model of chemical reactivity uncover and explain various trends in SN 2 reactivity along the nucleophiles F- , OH- , and NH 2 - , including solvent and counterion effects.