The rates and products of addition of 4-chlorobenzenesulfenyl chloride to 30 mono- and disubstituted alkenes have been determined in 1,1,2,2-tetrachloroethane at 25 °C. The rates of addition span a range of 106. No correlation with the extended Taft equation was found with the rates of all 30 compounds. The rate ratiokc/ktfor addition to nine pairs of isomericcis-transalkenes ranges from a low of 3.1 for the 2-butenes to a high of 1.57 × 105for the 2,2,5,5-tetramethyl-3-hexenes. The rate ratiokc/ktdoes not always increase regularly with the increasing size of the substituents which suggests that relief of ground state strain is not important in the rate determining transition state. Greater steric hindrance between the electrophile and thetransalkene compared to thecisisomer is proposed to account for the results.