Knowledge Bank

The Raman (3100 to $10cm-1$) and infrared (3100 to $30cm-1$) spectra of fluoromethyl phosphonic difluoride, $FCH2P(O)F2$, in the gas and solid phases have been recorded. Additionally, the Raman spectrum of the liquid along with qualitative depolarization ratios have also been obtained. These data have been interpreted on the basis of an equilibrium between the trans (fluorine atom trans to the oxygen atom) and gauche conformers in the gas and 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 solid. A $\Delta$H value has been determined from a study of the Raman spectrum for the liquid. Utilizing the trans torsional frequency, the gauche dihedral angle, and the enthalpy difference between the conformers, the potential function governing the interconversion of the rotamers has been calculated. A complete vibrational assignment is proposed for both conformers based on infrared band contours, Raman depolarization data, group frequencies, and normal coordinate calculations. The conformational stabilities, barriers to internal rotation, force constants, infrared and Raman intensities and fundamental vibrational frequencies, along with the structural parameters, have been obtain from ab initio Hartree-Fock gradient calculations employing either the RHF/3-21G* or RHF/6-31G* basis sets. The calculated Raman intensities with the 3-21G* basis set reproduce the observed Raman spectrum remarkably well.