Attila Kovács, Alexander Yu. Ivanov

Vibrational analysis of a-d-glucose trapped in Ar matrix

Journal of Physical Chemistry B, 113 (2009) 2151-2159

The FT-IR spectra of a-d-glucose have been investigated by means of matrix-isolation FT-IR spectroscopy in the 3700-200 cm^-1 range and by B3LYP/6-311++G** DFT calculations. The joint analysis of the experimental and computed IR spectra supported the expected predominance of the most stable gg and gt conformers in the vapor phase and the minor contribution of the less stable tg conformer. Weak absorption bands at the edge of the OH stretching region are in agreement with small amounts of analogous conformers with clockwise arrangement of the hydrogen bonds (c-gg, c-gt, c-tg). The assignment of the IR spectra was carried out on the basis of the computed harmonic force field using the scaled quantum mechanical (SQM) method of Pulay. Scale factors developed previously for the B3LYP/6-311++G** level proved to be well transferable except that for the OH torsion. The latter scale factor was adjusted on the basis of the present experimental data. Based on the calculated results 99 bands have been assigned to the gg, gt and tg conformers of a-d-glucose with average deviations of 5.0, 5.9 and 6.1 cm^-1, respectively.

Experimental matrix-IR spectrum of a-d-glucose in the 1500-600 cm^-1 range and the computed unscaled IR spectra of selected conformers.