Spectra and structure of organophosphorus compounds XLV. Vibrational spectra, conformational stability, ab initio calculations, and vibrational assignment of chloromethyl difluorophosphine and chloromethyl difluorophosphine- d2

Abstract

The IR (4000-50 cm −1) and Raman (4000-20 cm −1) spectra of chloromethyl difluorophosphine, ClCH 2PF 2, and chloromethyl difluorophosphine- d 2, ClCD 2PF 2, in the vapor (293 K) and solid phases (77 K) have been recorded. Additionally, the Raman (4000-50 cm −1) spectra of the liquid phase of these compounds along with qualitative depolarization ratios have also been obtained. These data have been interpreted on the basis of an equilibrium between trans (chlorine atom trans to phosphorus lone pair) and gauche conformers in the gas and liquid phases. Vapor phase IR contours along with the solvent and temperature effects have allowed the assignment of conformer doublet components to the individual conformers. From the study of the Raman spectrum of the liquid as a function of temperature a value of 167 ± 25 cm −1 (2.0 ± 0.3 kJ mol −1) has been determined for the enthalpy difference, with the trans rotamer more stable than the gauche conformer. In the vapor phase the gauche conformer strongly dominates, whereas the crystalline solid obtained at 77 K consists exclusively of the trans conformer. A complete vibrational assignment for both conformers of each isotopomer, based on IR contours, Raman depolarization data, group frequencies and normal coordinate calculations is proposed. The conformational stabilities, barriers to internal rotation, force constants and fundamental vibrational frequencies, along with the structural parameters, have been obtained from ab initio Hartree—Fock gradient calculations employing both the RHF/3-21G* and RHF/6-31G* basis sets.