Raman and infrared spectra, ab initio calculations, normal coordinate analysis, and conformational stability of 2-methoxypropene

The Raman (3500-40 cm(-1)) and infrared (3500-70 cm(-1)) spectra of gaseous and solid 2-methoxypropene, CH3O(CH3)C=CH2, and the isotopomers, CD3O(CH3) C=CH2 and CH3O(CD3)C=CD2 have been recorded. In addition, the Raman spectra of the liquids have been recorded with qualitative depolarization measurem ents. All of these data indicate that only one conformer is present in the fluid phases at ambient temperature and this form is the cis conformer, whi ch remains in the solid. Assignments are provided for the fundamentals of a ll three isotopomers for the cis conformer with C-s symmetry. The far-infra red spectra of all three isotopic species have been recorded at a resolutio n of 0.1 cm(-1) in the gas and 1.0 cm(-1) in the solid. The parameters of t he potential function governing the asymmetric torsion are determined to be V-3 = 1485 +/- 9 cm(-1) and V-6 = -55 +/- 4 cm(-1) for the do compound, wh ere only two terms were determined, since a second conformer was not eviden t. The barrier to internal rotation for the methyl group attached to the ox ygen atom is 1370 +/- 8 cm(-1) and the C-CH3 barrier is 772 +/- 5 cm(-1). A b initio calculations with full electron correlation have been carried out by the perturbation method to second order to obtain the equilibrium struct ural parameters, harmonic force constants, fundamental frequencies, infrare d intensities, Raman activities, depolarization values. and conformational stability. The predicted values have been compared to the experimental valu es where appropriate.