Raman and infrared spectra,conformational stability,barriers to internal rotation,r 0 structural parameters,ab initio calculations,and vibrational assignment for vinyl chloroformate

The Raman (3200 to 10 cm^–1) and infrared (3500 to 50 cm^–1) spectra of vinyl chloroformate, H₂C=CHOC(O)Cl, have been recorded for both the gas and solid. Additionally, the Raman spectrum of the liquid has been recorded, and depolarization ratios have been obtained. These data have been interpreted on the basis that the only stable conformation present at ambient temperature is thetrans-trans rotamer, where the firsttrans refers to the vinyl moiety relative to the O—CCl bond and the second to the C—Cl bond relative to the=C—O bond. Using harmonic rigid asymmetric top calculations, the infrared vapor phase contours for the C=O and the C=C stretch were predicted for thetrans-trans and for thecis-trans conformer, and were compared with experiment. For both fundamentals thetrans-trans hybrid reproduces the experimental contour, whereas thecis-trans contours fail to do so for both fundamentals. From far-infrared spectrum of the vapor obtained at 0.1 cm^–1 resolution, the C(O)Cl andO-vinyl torsional fundamentals have been observed at 132 and 61 cm^–1, respectively. Ther ₀ structural parameters have been obtained from a combination of ab initio calculated parameters with appropriate offset values and the fit of the microwave rotational constants for the two naturally occurring chlorine isotopes. The structure, barrier to internal rotation, and vibrational frequencies have been determined from ab initio Hartree-Fock gradient calculations, using the 3-21G^* and 6-31G^* basis sets. These results are compared to those obtained experimentally and to similar quantities for some related molecules.