This project describes and compares two methods of assessing the electronic properties of some phosphine ligands. The ligands PPh3, Ph2P(C6H4-3-CH3), PPh2C6H4-4-Cl, P(C6H4-4-Cl)3, PPh(C6H4-4-SCH3)2, P(C6H4-4-OCH3)3 were investigated. Additionally ligands of the type Ph2PR and PhPR2 where R = mesityl, cyclohexyl or adamantly were prepared by the reaction of Ph2PCl, PhPCl2 with the appropriate Grignard reagents. The selenides of these P(III) ligands were obtained by reaction of the phosphine with selenium in toluene under reflux over a period of a few hours. The 1J(PSe) coupling constants were determined for these compounds and ranged from 833 Hz in dimesityl phosphine selenide to 714 Hz in tris(p-anisyl)phosphine selenide.[Mo(CO)5P] complexes (P = P(III) ligand) were also obtained by the reaction of the phosphine with molybdenum hexacarbonyl in toluene with heating for 2 hours. The v(CO) stretching frequencies varied from 2072 cm-1 in tri-phenylphosphine molybdenum pentacarbonyl to 2069 cm-1 in bis(p-thioanisyl)phenylphosphine molybdenum pentacarbonyl.A comparison of the 1J(PSe) coupling constants of the phosphine selenides and v(CO) stretching frequency of the [Mo(CO)5P] complexes for these ligands, and others reported in the literature is made. From this it is shown the 1J(PSe) is a useful probe of the electronic effects of a phosphine ligand.