Vibrational analysis of hydroxyacetone

In order to be able to fully understand the vibrational dynamics of monosaccharide sugars, we started with hydroxyacetone CH2OHCOCH3, and glycolaldehyde CH2OHCOH, which are among the smallest molecules that contain hydroxyl and carbonyl group on neighboring carbon atoms. This sterical configuration is characteristic for saccharides and determines their biochemical activity. In this work vibrational analysis of hydroxyacetone was undertaken by performing the normal coordinate analysis for glycolaldehyde first, and transferring these force constants to hydroxyacetone. The observed Raman and infrared bands for 90 wt.% solution of hydroxyacetone in water (acetol) were used as a first approximation for the bands of free hydroxyacetone. The number of observed Raman and infrared bands for acetol exceeds the number of calculated values for the most stable hydroxyacetone conformer with Cs symmetry, which suggests more than one conformer of hydroxyacetone in water solution. In particular, there are two bands both in infrared (1083 and 1057 cm−1) and in Raman spectrum (1086.5 and 1053 cm−1) that are assigned to the CO stretching mode and this is one of the indicators of several hydroxyacetone conformers in the solution. Additional information was obtained from low temperature Raman spectra: at 240 K a broad assymmetric band centered around 280 cm−1 appears, suggesting a disorder in the orientation of hydroxyl groups. Glassy state forms at ∼150 K. The broad band at 80 cm−1 is assigned to frozen torsions of hydroxymethyl groups.