Series of isomeric mono-, di-, and triseleno-substituted alkenes have been synthesized and subjected to I7Se NMR analysis. In di-and triselenesubstituted alkenes stereochemical assignments were obtained by measurements of 77Se-77Se coupling constants. Values between 117-77 Hz for cis 3J~ e-~ e, 55-19 Hz for 2J~ e~ e, and 12-2 Hz for trans 3Jbse were found. A large body of vinylic 77Se-1H coupling constants has been obtained in di- ...