CONFORMATIONAL BEHAVIOR OF ETHYLOXIRANE FROM INFRARED AND RAMAN-SPECTRA, TEMPERATURE-DEPENDENT FT-IR SPECTRA OF XENON SOLUTIONS, AND AB-INITIO CALCULATIONS

Infrared spectra (3500-400 cm(-1)) of gaseous ethyloxirane, C-OC2H2C2H 5, (1,2-epoxybutane) and xenon solutions of this molecule at temperatu res from -60 to -100 degrees C have been recorded. In addition, Raman spectra of the liquid and polycrystalline phases have been obtained, a nd variable temperature Raman spectra (25 to -89 degrees C) of the liq uid were also recorded. Spectroscopic evidence for the co-existence of the gauche-l and gauche-2 conformers of the title compound is found i n the fluid phases, along with small amounts of the cis rotameric form . In xenon solutions, the enthalpy difference between the gauche-l and gauche-2 conformers has been determined to be 217 +/- 34 cm(-1) (620 +/- 97 cal mol(-1)), with the gauche-l rotamer the more stable form, w hereas in the liquid phase this quantity is estimated to be 95 +/- 6 c m(-1) (272 +/- 17 cal mol(-1)). In the annealed solid phase, only the gauche-l conformer is found. Ab initio calculations, have been carried with different basis sets up to MP2/6-31G from which structural para meters and conformation stabilities have been determined. These calcul ations support the experimental conformational conclusions. A force fi eld from these calculations is used to support the vibrational assignm ents and simulate the observed infrared and Raman spectra. These resul ts are compared to the corresponding quantities for some similar molec ules.