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Raman and infrared spectra, conformational stability, barriers to internal rotation and ab initio calculations of allyl cyanide
Author(s) -
Durig James R.,
Guirgis Gamil A.,
Drew A. S.
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.1250251203
Subject(s) - conformational isomerism , raman spectroscopy , chemistry , dihedral angle , infrared , enthalpy , infrared spectroscopy , ab initio , crystallography , analytical chemistry (journal) , computational chemistry , molecule , thermodynamics , hydrogen bond , organic chemistry , physics , optics
The Raman (3200–10 cm −1 ) and infrared (3150–50 cm −1 ) spectra of allyl cyanide, CH 2 CHCH 2 CN, were recorded for the gas and solid phases. Additionally, the Raman spectrum of the liquid was recorded and qualitative depolarization values were obtained. Both the cis and gauche conformers are present in the gas and liquid phases with the cis conformer being the more stable rotamer and the only conformer present in the annealed solid. The fundamental asymmetric torsion of the cis conformer has been observed in the far‐infrared spectrum of the gas at 141.3 cm −1 with three excited states falling to lower wavenumbers. The corresponding fundamental for the gauche conformer has been observed in the Raman spectrum of the gas at ca. 102 cm −1 . From temperature‐dependent studies of the Raman spectrum of the liquid, three pairs of conformer peaks have been used to determine the Δ H value of 245 ± 6 cm −1 (707 ± 17 cal mol −1 ), with the cis conformer the most stable rotamer. Additionally, a variable‐temperature study of the infrared spectrum of the sample dissolved in liquified xenon gives a Δ H of 336 ± 61 cm −1 (961 ± 175 cal mol −1 ), which should closely represent the Δ H value for the gas. Utilizing the torsional transitions, the enthalpy difference and the gauche dihedral angle, the potential function governing the conformational interchange was determined. A complete vibrational assignment is proposed for the cis conformer and several fundamentals are identified for the gauche rotamer based on infrared band contours, Raman depolarization data, group wavenumbers, relative intensities and normal coordinate calculations. The experimental conformational stability, barriers to internal rotation, structural parameters and fundamental vibrational wavenumbers are 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.