Spectra and structure of organophosphorus compounds : L-Raman and infrared spectra, conformational stability, ab initio calculations, and vibrational assignment of fluoromethylphosphoric dichloride
Faculty of Sciences. Chemistry
Journal of Raman spectroscopy. - Dordrecht
, p. 869-886
University of Antwerp
The Raman (3100-10 cm(-1)) and infrared (3100-30 cm(-1)) spectra of fluoromethylphosphonic dichloride FCH2P(O)Cl-2, in the gas and solid phases were recorded. The Raman spectrum of the liquid along with qualitative depolarization ratios were obtained. These data, along with infrared vapor-phase contours, were interpreted on the basis of an equilibrium between trans (fluorine atom trans to the oxygen atom) and gauche conformers in the gas aod liquid phases, with the trans conformer being the more stable form in both of these physical states and the only form present in the crystalline sold. From the study of the Raman spectrum 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. Utilizing the trans torsional wavenumber, the gauche dihedral angle and the enthalpy difference between conformers, the potential function governing the interconversion of the rotamers was estimated. A complete vibrational assignment is proposed for both conformers based on infrared band contours, Raman depolarization data, group wavenumbers and normal coordinate calculations. The conformational stabilities, barriers to internal rotation, force constants, infrared and Raman intensities aod fundamental vibrational wavenumbers, along with the structural parameters, were obtained from ab initio Hartree-Fock gradient calculations employing both the RHF/3-21G* and RHF/6-31G* basis sets. The calculated Raman intensities with the 3-21G* basis set reproduce the observed Raman spectrum remarkably well. Many of these results were compared with the corresponding quantities for some similar molecules.