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Spectra and structure of organosphosphorus molecules. Part LX—Raman and infrared spectra, conformational stability, ab initio calculations and vibrational assignment of fluoromethyldichlorophosphine †
Author(s) -
Durig J. R.,
Honeycutt T. R.,
Daeyaert F. F. D.,
Robb J. B.
Publication year - 1999
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/(sici)1097-4555(199903)30:3<155::aid-jrs364>3.0.co;2-4
Subject(s) - conformational isomerism , raman spectroscopy , ab initio , ab initio quantum chemistry methods , chemistry , enthalpy , infrared , infrared spectroscopy , computational chemistry , crystallography , molecule , thermodynamics , organic chemistry , physics , optics
The Raman spectra (3500–30 cm −1 )of gaseous, liquid and solid and the infrared spectra(3500–400 cm −1 ) of gaseous and solidfluoromethyldichlorophosphine, FCH 2 PCl 2 , wererecorded. The data indicate that two conformers are present in thefluid states where the gauche conformer is the predominantspecies but only the trans rotamer (the F atom on themethyl group is trans to the phosphorus lone pair ofnon‐bonded electrons) remains in the crystalline solid.The enthalpy, ΔH, was determined to be 165±8 cm −1 (472±24 cal mol −1 ); 1 cal=4.184 J with the gauche conformermore stable from the sample dissolved in liquified xenon utilizingthe bands assigned to the CH 2 rocks for the twoconformers. Additionally, utilizing six Raman lines in the spectrumof the liquid and adjusting for their ab initio ‐predicted relative intensities, the enthalpy differencewas determined to be 156±67 cm −1 (447±193 cal mol −1 ), again with the gauche conformer the more stable form. These values are inagreement with the 273 cm −1 energy differenceobtained from ab initio MP2/6–311++G** calculations. Completevibrational assignments are proposed for both conformers based oninfrared band contours, Raman and infrared relative intensities andgroup wavenumbers, which are supported by normal coordinatecalculations utilizing the force constants from ab initio MP2/6–31G* calculations. The optimized geometries,conformational stabilities, harmonic force fields, infraredintensities, Raman activities, depolarization ratios and vibrationalwavenumbers are reported for both conformers fromRHF/6–31G* and/or MP2/6–31G* abinitio calculations. The calculated quantities are compared withthe experimentally determined values where applicable and also withsome corresponding results for some similar molecules. Copyright© 1999 John Wiley & Sons, Ltd.