INFRARED AND RAMAN-SPECTRA, CONFORMATIONAL STABILITY, BARRIERS TO INTERNAL-ROTATION, AB-INITIO CALCULATIONS AND VIBRATIONAL ASSIGNMENT OF ETHYL METHYL SELENIDE

The Raman spectra (3200-10 cm-1) of ethyl methyl selenide in the gas, liquid and solid phases and the infrared spectra (3200-30 cm-1) of the gas and solid have been recorded. Qualitative depolarization ratios have been obtained for the lines in the Raman spectrum of the liquid. By a variable temperature Raman study of the liquid, it has been determined that the gauche conformer is more stable than the trans rotamer by 158 +/- 16 cm-1 (452 +/- 46 cal mol-1), and the gauche conformer is the rotamer present in the solid. A complete vibrational assignment for the gauche conformer is presented. All of these data are compared to the corresponding quantities obtained from ab initio Hartree-Fock gradient calculations employing the STO-3G* and 4-31G*/MIDI-4* basis sets. Complete equilibrium geometries have been calculated for both rotamers and the results are discussed and compared with the corresponding quantities for some similar molecules.