SPECTRA AND STRUCTURE OF ORGANOPHOSPHORUS COMPOUNDS Part XXVII. Infrared and Raman spectra and conformational stability of ethyldimethylphosphine sulfide

Article abstract of DOI:10.1016/0022-2860(86)87026-0

The Raman (10 to 3500 cm^-1) and infrared (50 to 3500 cm^-1) spectra have been recorded for solid ethyldimethylphosphine sulfide, CH3CH2P(S)(CH3)2.Additionally, the Raman spectrum of the liquid phase has been recorded and qualitative depolarization values have been obtained.From the fact that several distinct lines appear on going from the solid phase to the fluid state, it is concluded that the molecule exists as a mixture of the gauche and trans conformers in the liquid phase.A study of solutions of ethyldimethyphosphine sulfide in solvents of varying dielectric constants indicates that it is the gauche conformer which is more stable and the only one which remains in the solid state.Relying on group frequencies as well as relative depolarization values and relative intensities of the infrared and Raman bands, a complete vibrational assignment is proposed for the gauche conformer.The assignment is supported by a normal coordinate calculation which was carried out utilizing a modified valence force field to obtain the frequencies of the normal modes and the potential energy distribution.The asymmmetric torsional mode for the gauche conformer has been assigned to the broad band at 110 cm^-1 in the infrared spectrum of the solide phase.All of these results are compared with corresponding quantities for several other organophosphines.