# CONFORMATIONAL STABILITY OF $CH_{3}CH_{2}P(Z)F_{2} (Z=O,S)$ FROM TEMPERATURE DEPENDENT FT-IR SPECTRA OF RARE GAS SOLUTIONS AND $r_{0}$ STRUCTURAL PARAMETERS

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 Title: CONFORMATIONAL STABILITY OF $CH_{3}CH_{2}P(Z)F_{2} (Z=O,S)$ FROM TEMPERATURE DEPENDENT FT-IR SPECTRA OF RARE GAS SOLUTIONS AND $r_{0}$ STRUCTURAL PARAMETERS Creators: Xiao, Jinpeng; Robb, J. B., II; Durig, J. R. Issue Date: 1999 Publisher: Ohio State University Abstract: Variable temperature $(-55 to -150^{\circ}C)$ studies of the infrared spectra $(3500 to 400 cm^{-1})$ of ethylphosphonic difluoride. $CH_{3}CH_{2}P(O)F_{2}$ and ethylphosphonothioic difluoride, $CH_{3}CH_{2}P(S)F_{2}$ dissolved in liquid xenon or krypton have been recorded. From these data, the enthalpy differences have been determined to be $76\pm 9 cm^{-1} (0.91\pm 0.11 kJ/mol)$, for $CH_{3}CH_{2}P(O)F_{2}$ with the trans conformer the more stable rotamer and $53\pm 7$ $cm^{-1}(0.63\pm 0.08kJ/mol)$ for $CH_{3}CH_{2}P(S)F_{2}$ but with the gauche conformer the more stable form. Complete vibrational assignments are presented for both molecules, which are consistent with the predicted frequencies obtained from the ab initio MP2/6-31G(d) calculations. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, and depolarization ratios have been obtained from RHF/6-31G(d) and/or MP2/6-31G(d) ab initio calculations. These quantities are compared to the corresponding experimental quantities when appropriate as well as with some corresponding results for some similar molecules. The $r_{0}$ adjusted structural parameters have been obtained for both molecules from a combination of the microwave rotational constants and ab initio predicted parameters. The corresponding $r_{0}$ structural parameters have been obtained for some similar molecules for comparison. Description: Author Institution: Department of Chemistry, University of Missouri-Kansas City URI: http://hdl.handle.net/1811/19281 Other Identifiers: 1999-MI-03