Micellar rate effects on hydrolyses of substituted benzoyl chlorides, 1, depend on headgroup charge and electron donation or withdrawal by substituents. Micellized sodium dodecyl sulfate, SDS, inhibits hydrolyses, and first-order rate constants in the micellar pseudophase, k'(M), decrease, relative to those in water, k'(W), over a range of ca. 10, but in cetyl trimethylammonium chloride, CTACl, k'(M)/k'(W) > 1 for hydrolyses of 1,3,5-(NO2)(2) and 1, 4-NO2, and decreases steeply with electron-donating substituents in the following sequence: 1,4-Cl approximate to 4-Br > 4-H > 4-Me > 4-OMe, over a range of > 10(3). Cetyl trimethylammonium bromide and mesylate behave like CTACl. Fits to the Hammett equation give rho approximate to 1 in SDS and rho approximate to 4 in CTACl. Anionic micelles have higher interfacial polarities than cationic micelles, but micellar and solvent effects do not correspond because over a range of solvents, H2O to H2O-MeCN, 1:1 w/w plots of log k'(W) against sigma go through minima with positive rho for 1, 3,5-(NO2)(2), and 4-NO2 and negative for the other substrates. The micellar effects correspond to differing extents of bond-making and -breaking in the transition state. Values of k(+)/k(-) (rate constants in CTACl and SDS) decrease strongly with increasing electron donation by substituents. Micellar rate effects in hydrolyses of benzyl bromide and 4-methoxybenzyl chloride are similar to those with the benzoyl chlorides. Although data were analyzed by a pseudophase treatment, application of transition state theory and reported micellar surface potentials allows estimation of local charge at the reaction center for hydrolyses of the benzoyl chlorides.