Some m- and p-substituted t-butylphenyl carbonyl chlorides have been prepared, and their rates of solvolysis in aqueous ethanol have been determined. By applying the Hammett equation, it has been shown that there is no steric inhibition of mesomerism in the intermediate carbonium ions formed in the reactions. The role of steric effects in the solvolysis has been discussed, and explanations for the slow rates of reaction have been considered.