The S N 2 substitution reactions between methyl naphthalene-2-sulfonate and methyl 4-nitrobenzenesulfonate with bromide ions were studied in alkanediyl-a,xbis(dimethyldodecylammonium) bromide, 12-s-12,2Br -(s = 3, 4, 6), micellar solutions in the absence and in the presence of alcohols. The observed rate constant for the two processes was found to be sensitive to changes in micellar characteristics caused by the presence of alcohols. At high surfactant concentrations, kinetic data made evident the sphere-to-rod transition accompanying the increase in the dimeric surfactant concentration in all the micellar reaction media investigated. Kinetic results were quantitatively rationalized within the whole surfactant concentration range, below and above the second CMC, by using a new treatment based on the pseudophase kinetic model.