Raman and infrared spectra, conformational stability, barriers to internal rotation, ab initio calculations and vibrational assignment for vinyl fluoroformate

Abstract

AbstractThe Raman spectra (3200—10 cm−1) and infrared spectra (3500—50 cm−1) of vinyl fluoroformate, H2CCHOC(O)F, were recorded for both the gas and solid. Additionally, the Raman spectrum of the liquid was recorded and depolarization ratios were obtained. These data have been interpreted on the basis that the only stable conformation present at ambient temperature is the trans‐trans, where the first trans refers to the vinyl moiety relative to the OCFO bond and the second trans to the CF bond relative to the CO bond. Anharmonic rigid asymmetric top calculations were used to predict the CO and CC stretch infrared vapor‐phase contours for the trans‐trans and the cis‐trans conformers. For both conformers, the predicted CO stretch contour agrees with the experimentally observed contour. For the CC stretch, only the contour predicted for the trans‐trans conformer reproduces the experimental contour. From the far‐infrared spectrum of the vapor obtained at a resolution of 0.1 cm−1, the methoxy and O‐vinyl torsional fundamentals have been observed at 153 and 63 cm−1, respectively. The structure, barrier to internal rotation and vibrational frequencies were also determined from ab initio Hartree‐Fock gradient calculations using both the 3—21G and 6—31G* basis sets. These results are compared with theos obtained experimentally and to similar quantities for some related molecules.