5-Vinyl-2-norbornene is epoxidized with tert-butyl, tert-amyl, or cumyl hydroperoxide in the presence of molybdenyl ethanediolate at either or both of the double bonds of the hydrocarbon to afford preferentially 2,3-epoxy-5-vinylnorbornane. The reactivity of tert-alkyl hydroperoxides correlates with their structure characterized by the Taft polar substituent constants. The rho* value found to be 1.08 confirms the electrophilic character of the catalytic hydroperoxide epoxidation and indicates a low polarity of the activated complex of the reaction.