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Raman and infrared spectra, conformational stability, vibrational assignment, barriers to internal rotation and ab initio calculations of but‐2‐enoyl chloride
Author(s) -
Durig J. R.,
Groner Christian U.,
Costner T. G.,
Wang Aiying
Publication year - 1993
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.1250240602
Subject(s) - conformational isomerism , raman spectroscopy , chemistry , enthalpy , infrared , internal rotation , ab initio , infrared spectroscopy , crystallography , chloride , ab initio quantum chemistry methods , spectral line , computational chemistry , stereochemistry , molecule , thermodynamics , organic chemistry , mechanical engineering , physics , astronomy , optics , engineering
The Raman (3500–10 cm −1 ) and infrared (3200–50 cm −1 ) spectra were recorded for the fluid and solid phases of but‐2‐enoyl chloride (crotonyl chloride), trans ‐CH 3 CHCHCClO, where the methyl group is trans to the CClO group, and a complete vibrational assignment is proposed. These data were interpreted on the basis that the s‐trans (anti) form (two double bonds oriented trans to one another) is the most stable form in the fluid phases and the only conformer remaining in the solid state. The asymmetric torsional fundamental of the more stable s‐trans and the higher energy s‐cis (syn) form were observed at 97.5 and 86.9 cm −1 , respectively. From these data the asymmetric potential function governing the internal rotation about the CC bond was determined. The potential coefficients are V 1 = −111 ± 2, V 2 = 1860 ± 48, V 3 = 6 ± 2, V 4 , = −43 ± 24 and V 6 = −22 ± 6. The s‐trans to s‐cis and s‐cis to s‐trans barriers were determined to be 1890 and 1785 cm −1 , respectively, with an enthalpy difference between the conformers of 105 ± 52 cm −1 [300 ± 149 cal mol −1 (1 cal = 4.184 J)]. Similarly, the barrier governing internal rotation of the CH 3 group for the s‐trans conformer was also determined to be 912 ± 30 (2.61 ± 0.09 kcal mol −1 ) from the torsional fundamental observed in the far‐infared spectrum of the gas. All these data were compared with the corresponding quantities obtained from ab initio Hartree–Fock gradient calculations employing the RHF/3–21G*, RHF/6–31G* and/or MP2/6–31G* basis sets. These results were compared with the corresponding quantities for some similar molecules.