CONFORMATIONAL ANALYSIS OF A SERIES OF CH3MH2OM′H2CH3 (M, M′ = C AND Si) BY RAMAN SPECTROSCOPY AND DENSITY FUNCTIONAL THEORY

Abstract: Raman spectra in the liquid and solid states for a series of diethyl ether and its organosilicon derivatives, CH3MH2OM′H2CH3 (M, M′ = C and Si), were measured. Normal vibrations of these molecules were assigned by using density functional theory with the B3LYP/6-31G * and B3LYP/6-311+G* * methods. Stable molecular forms in the liquid and solid states have been discussed. Vibrational spectroscopy is a powerful technique to obtain information on various structural properties of molecules, and normal coordinate analysis of molecules is useful for the assignments of the spectra. Normal coordinate analysis by empirical force field calculation was, however, rather complicated for large molecules. In recent years, theoretical calculations by density functional theory (DFT) have afforded accurate vibrational wavenumbers for many molecules. A number of interests have been focused on the conformational stability of diethyl ether (DEE) in previous experimental and theoretical studies [1−11]. Although, a molecule of DEE has nine possible rotational isomers with respect to the two skeletal axes, the number of independent isomers is reduced, owing to the existence of mirror image isomers, to four, TT, TG, GG and GG′, where the first and second symbols designate the conformations (T: trans; G: gauche) about th