Zwitterionic micelles of tetradecyldimethylammoniopropanesulfonate and tetradecyldibutylammoniopropanesulfonate, SB3-14 and SBBu3-14, respectively, accelerate the E2 reaction of OH À with 4-nitrophenethyl bromide (1b), but the reaction of phenethyl bromide (1a) is inhibited by SB3-14 and is only slightly accelerated by SBBu3-14. Analysis of these data allows the separation of the association constants for transfer of reactants from water to micelles from the second-order rate constants in the micelles. These second-order rate constants are, as in water, larger for 1b than 1a, and for both substrates are higher in SBBu3-14 than in SB3-14, as found for reactions in otherwise similar cationic micelles. Rate constants in micelles, relative to those in water, are consistently higher in E2 than in S N 2 reactions.