The orientation of sodium 4-chloro-3,5-dinitrobenzoate (1), sodium 2-chloro-3,5-dinitrobenzoate (2), sodium 4-fluoro-3-nitrobenzoate (3), and sodium 2-fluoro-5-nitrobenzoate (4) in micelles of cetyltrimethylammonium bromide (CTAB) has been determined by 1and 19F NMR studies. Rate constants for the hydroxydehalogenation of compounds 1-4 in water and in CTAB (0.1-40 mM) have been determined. The observed rate constants over this range of CTAB concentration have been treated by a computer program to determine the best values for the rate constant for reaction in the micellar pseudophase (k2m), the binding constant (Ks), and the exchange constant of nucleophile and micellar counterion (KBrOH). In all cases, the rate constant within the micelle (k2m) is less than in water (k2w). For compounds 2 and 4, where the reaction center is close to the micelle–water interface, k2mis a higher percentage of k2wthan for compounds 1 and 3, where the reaction center is buried deeper inside the micelle. Significant catalysis was observed at CTAB concentrations below the normally accepted critical micelle concentration (cmc) of CTAB. Plots of rate versus CTA concentration between 0.1 and 1 mM indicate that, under these reaction conditions, the cmc of CTAB is 3 X 10-4M. After allowing for the different activation provided by the nitro groups of compounds 1 and 2, the para/ortho rate ratio for the carboxylate group was calculated to be 34 (in water) and 18.5 (in CTAB). Similarly, for compounds 3 and 4, the para/ortho rate ratio for CO2-was found to be 600 (in water) and 348 (in CTAB). © 1988, American Chemical Society. All rights reserved.