Phenyldimethylcarbinyl chloride, p-nitrobenzoate, and thionbenzoate have been found to be more reactive than the corresponding benzhydryl compounds by factors of 5.5, 23, and 4700, respectively, in ethanolysis at 50°. For the cumyl derivatives, kinetic isotope effects and solvolysis products are consistent with an ionization-type reaction for the three leaving groups. The results are interpreted in terms of an observed kinetic isotope effect containing contributions from the isotope effect on elimination from the carbonium ion because of ion-pair return. The high reactivity of cumyl thionbenzoate is attributed to a decrease in the importance of ion-pair return in this system relative to the model compounds. © 1969, American Chemical Society. All rights reserved.