A re-examination of the ‘unified’SN2–E2 mechanism

Abstract

Rates and product proportions for the reactions of 1-phenylethyl and phenethyl bromides with sodium and potassium ethoxides in ethanol, in the absence and presence of sodium perchlorate, are reported. When consideration of the separate reactions of free ethoxide ions and metal ethoxide ion-pairs is taken, the data can be successfully interpreted in terms of competing E1, E2, S_N1, and S_N2 processes. The Sneen–Robbins mechanistic alternative, in which is postulated an ion-pair intermediate common to both substitution and elimination processes, gives a less satisfactory account of the results.