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Raman and infrared spectra, conformational stability, barriers to internal rotation and ab initio calculations of fluorocarbonyl isocyanate
Author(s) -
Durig J. R.,
Guirgis G. A.,
Krutules K. A.,
Phan H.,
Stidham H. D.
Publication year - 1994
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/jrs.1250250306
Subject(s) - conformational isomerism , raman spectroscopy , chemistry , infrared , ab initio , ab initio quantum chemistry methods , isocyanate , infrared spectroscopy , molecule , crystallography , computational chemistry , analytical chemistry (journal) , organic chemistry , physics , optics , polyurethane
The Raman (3100–10 cm −1 ) and infrared (3100–30 cm −1 ) spectra of fluorocarbonyl isocyanate, FC(O)NCO, were recorded for the gas and solid. Additionally, the Raman spectrum of the liquid was recorded and qualitative depolarization values were obtained. The observed bands are assigned on the basis of the more stable cis conformer (isocyanate group cis to the carbonyl bond) in the fluid states but only the trans conformer remains in the annealed solid. From temperature dependence studies of the Raman spectra of the gas and liquid, two pairs of conformer peaks were used to determine Δ H values of 258 ± 47 cm −1 (738 ± 134 cal mol −l ) and 140 ± 29 cm −1 (400 ± 83 cat mol −1 ), respectively, with the cis conformer the more stable rotamer in both phases. Additionally, variable‐temperature studies of the infrared spectrum of the sample dissolved in liquified Kr gave Δ H = 150 ± 28 cm −1 (429 ± 80 cal mol −1 ), which should closely represent the Δ H value for the gas. A complete vibrational assignment is proposed for both conformers based on infrared bard contours, Raman depolarization data, group frequencies, relative intensities and normal coordinate calculations. The experimental conformational stability, barriers to internal rotation, structural parameters and fundamental vibrational wavenumbers were compared with those obtained from ab initio gradient calculations employing the RHF/3–21G, RHF/6‐31G* and /or MP2/6‐31G* basis sets and to the corresponding quantities obtained for some similar molecules.