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 ≈ 4-Br > 4-H > 4-Me > 4-OMe, over a range of >103. Cetyl trimethylammonium bromide and mesylate behave like CTACl. Fits to the Hammett equation give ρ ≈ 1 in SDS and ρ ≈ 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 σ go through minima with positive ρ for 1, 3,5-(NO2)2, and 4-NO2 and negative for t...