Vibrational analysis of hydroxyacetone

Abstract

In order to be able to fully understand the vibrational dynamics of monosaccharide sugars, we started with hydroxyacetone CH 2 OHCOCH 3, and glycolaldehyde CH 2 OHCOH, 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 C s 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.

Computational thermochemistry of glycolaldehyde

“…[14] A number of the experimental investigations were augmented by computational modeling as well. [9,11] Four minima are identified, described by two torsion angles s 1 (O¼ ¼CACO) and s 2 (CCAOH). Of these, the most stable is the cis-cis (Cc: s 1 ¼ 0 and s 2 ¼ 0 ) form which enjoys a degree of AOH…O¼ ¼hydrogen bonding.…”

“…This departure from coplanarity is not supported by other studies and may be an artifact of the large‐amplitude low‐frequency torsional motion of the CHO fragment relative to the CH 2 OH fragment. The IR spectrum of cis‐cis glycolaldehyde has been reported for the vapor8, for the species in water solution9 and for the species isolated both in rare gas10 and para‐hydrogen11 matrices. In Ar, Kr, and Xe matrices irradiation by broadband infrared light produces the trans‐trans conformer.…”

“…The potential surface for glycolaldehyde has been investigated computationally at the RHF/6‐31G(d) level by Aspiala et al10 and more thoroughly in MP2/cc‐pVDZ and cc‐pVTZ by Ratajczyk et al13 and in MP4(SDTQ)/cc‐pVQZ//MP2/cc‐pVQZ by Senent 14. A number of the experimental investigations were augmented by computational modeling as well 9, 11. Four minima are identified, described by two torsion angles τ 1 (OCCO) and τ 2 (CCOH).…”

Extended analysis of hydroxyacetone in the torsional ground state

“…First to consider are the excited torsional/vibrational states, which can interact with and perturb the ground state if they sufficiently low in energy. Hydroxyacetone has several low-lying excited states, most importantly the methyl torsion, which has been calculated to lie near 65 cm À1 (but which is too weak to have been observed in Raman spectra), and the CH 2 OH torsion that has been measured at 80 cm À1 [24]. Additional low-lying bands that are experimentally observed are the OCC in plane bending mode at 276 cm À1 and the OH torsion at 330 cm À1 [24], both of which could potentially impact the rotational spectrum of the ground state.…”

“…Hydroxyacetone has several low-lying excited states, most importantly the methyl torsion, which has been calculated to lie near 65 cm À1 (but which is too weak to have been observed in Raman spectra), and the CH 2 OH torsion that has been measured at 80 cm À1 [24]. Additional low-lying bands that are experimentally observed are the OCC in plane bending mode at 276 cm À1 and the OH torsion at 330 cm À1 [24], both of which could potentially impact the rotational spectrum of the ground state. The importance of these low-lying excited states is confirmed by the presence of many unassigned lines in our data with similar or larger intensity than the ground state.…”