The effect of substituents in the phenyl ring of both the electrophile and the alkene has been studied in the reaction of areneselenenyl chlorides and (E)-and (2)-1-phenylpropenes. Electron-donating groups in both phenyl rings enhance the rate of reaction. Viewing this reaction as a nucleophilic displacement at bivalent selenium leads to a model that allows the possibility of reaction by a continuum of mechanisms. These mechanisms differ only in ...