2,4-Dinitrophenylselenium trichloride has been found to add to cis- and trans-1-phenylpropene in an anti stereospecific manner to yield threo-dl-and erythro-dl-β-chloroalkyl 2,4-dinitrophenyl selenide dichlorides, respectively. Comparison is made with the adducts from the addition of 2,4-dinitrobenzeneselenenyl chlorides. β-Chloroalkyl 2,4-dinitrophenyl selenides react with chlorine or sulfuryl chloride to yield β-chloroalkyl 2,4-dinitrophenyl selenide dichlorides. β-Chloroalkyl selenide dichlorides were observed to decompose into 1,2-dichloro adducts and areneselenenyl chloride. 2,4-Dinitrobenzeneselenenyl acetate was shown to add to alkenes in an anti stereospecific manner.