Samples of 4-t-butyl-, 2,6 dimethyl-, 2,4,6-trimethyl-, and 2,6-dimethyl-4-t-butyl-benzophenones have been prepared. The dissociation constants of the conjugate acids of these ketones, together with benzophenone and 4-methylbenxo-phenone, have been measured by a spectrophotometric method. The results cannot be explained by the current concepts for the electronic effects of alkyl groups.