Ab initio calculations of vibrational spectra of 2-methoxy ethanol in the C–H stretching range

Abstract

Focussing on the range of the C–H stretching vibrations, spectra of 2-methoxy ethanol (HO–CH₂–CH₂–O–CH₃) were calculated at the MP2 level using the 6-31+G(d) basis set. The spectra exhibit a striking dependence on the molecular conformation which can cause shifts of mode frequencies by up to 80 cm⁻¹. Whereas vibrations above 2955 cm⁻¹ are very characteristic for OH in a gauche conformation, the spectral range between 2850–2900 cm⁻¹ is congested by numerous bands and, therefore, seems poorly suited for analytical purposes. In this range, even the unambiguous assignment of modes becomes impossible due to the overlap of symmetric and antisymmetric modes. The range between 2900 and 2955 cm⁻¹ is characterized by a grouping of the bands. The interaction of methoxy ethanol with water lifts this grouping and yields a more uniform distribution. The results are compared to a recent spectroscopic study of oligo(ethylene glycol) films (Dreesen et al., Chem Phys Lett., 2001, 333, 327). For the films in contact with air the characteristic spectral features are well reproduced and changes induced by water are also reflected in the calculations.