Rates of solvolysis in 80% ethanol have been determined for 2-(3-isothiazolyl)-2- chloropropane, 2-(4-isothiazolyl)-2-chloropropane, and 2-(5-isothiazolyl)-2-chloropropane. From these rates and the rates of solvolysis of cumyl chlorides bearing electron-withdrawing substituents u+ values appropriate for the replacement of the benzene ring by an isothiazolyl moiety have been determined.