Sn2/E2 Branching in Protic Solvents: A Mechanistic Study

Abstract

We present calculations for <TEX>$S_N$</TEX>2/E2 reactions in protic solvents (t-butyl alcohol, ethylene glycol). We focus on the role of the hydroxyl (-OH) groups in determining the <TEX>$S_N$</TEX>2/E2 rate constants. We predict that the ion pair E2 mechanism is more favorable than the naked ion E2 reaction in ethylene glycol. E2 barriers are calculated to be much larger (~ 9 kcal/mol) than <TEX>$S_N$</TEX>2 reaction barriers in protic solvents, in agreement with the experimental observation [Kim, D. W. et al. J. Am. Chem. Soc. 2006, 128, 16394] of no E2 products in the reaction of CsF in t-butyl alcohol.