Spectra and structure of organophosphorus compounds. LVII. Raman and infrared spectra, conformational stability, and ab initio calculations for methoxydifluorophosphine

Abstract

The Raman (3500 to 20 cm −1) and infrared spectra (3500 to 40 cm −1) of gaseous and solid methoxydifluorophosphine, CH 3OPF 2, have been recorded. Additionally, the Raman spectrum of the liquid has been recorded from 3500 to 50 cm −1 and qualitative depolarization values have been obtained. These data have been interpreted on the basis that only the trans conformer (methyl group trans to the phosphorous lone pair) is present in all three physical states and a complete vibrational assignment is given for the normal and d 3 isotopomer. Ab initio calculations have been carried out with the RHF/3-21G* and RHF/6-31G* basis sets, as well as with electron correlation at the MP2 level with the 6-31G* basis set to obtain the structural parameters, relative conformational stabilities, fundamental frequencies, and infrared and Raman intensities. The fundamental vibrational frequencies and barriers to internal rotation which have been obtained experimentally are compared to those obtained with MP2/6-31G* basis set. From the ab initio calculations, the gauche conformer is estimated to be more than 4.6 kcal mol −1 less stable than the trans conformer. All of these results are discussed and compared with the corresponding quantities obtained for some similar molecules.