SPECTRA AND STRUCTURE OF ORGANOPHOSPHORUS COMPOUNDS .50. RAMAN AND INFRARED-SPECTRA, CONFORMATIONAL STABILITY, AB-INITIO CALCULATIONS AND VIBRATIONAL ASSIGNMENT OF FLUOROMETHYLPHOSPHONIC DICHLORIDE

The Raman (3100-10 cm(-1)) and infrared (3100-30 cm(-1)) spectra of fl uoromethylphosphonic dichloride FCH2P(O)Cl-2, in the gas and solid pha ses were recorded. The Raman spectrum of the liquid along with qualita tive depolarization ratios were obtained. These data, along with infra red vapor-phase contours, were interpreted on the basis of an equilibr ium between trans (fluorine atom trans to the oxygen atom) and gauche conformers in the gas aod liquid phases, with the trans conformer bein g the more stable form in both of these physical states and the only f orm present in the crystalline sold. From the study of the Raman spect rum for the liquid as a function of temperature, a value of 277 +/- 66 cm(-1) (792 +/- 189 cal mol(-1)) was determined for Delta H. Utilizin g the trans torsional wavenumber, the gauche dihedral angle and the en thalpy difference between conformers, the potential function governing the interconversion of the rotamers was estimated. A complete vibrati onal assignment is proposed for both conformers based on infrared band contours, Raman depolarization data, group wavenumbers and normal coo rdinate calculations. The conformational stabilities, barriers to inte rnal rotation, force constants, infrared and Raman intensities aod fun damental vibrational wavenumbers, along with the structural parameters , were obtained from ab initio Hartree-Fock gradient calculations empl oying both the RHF/3-21G and RHF/6-31G* basis sets. The calculated Ra man intensities with the 3-21G basis set reproduce the observed Raman spectrum remarkably well. Many of these results were compared with th e corresponding quantities for some similar molecules.