A Raman and infrared study of crystalline D-fructose, L-sorbose, and related carbohydrates. Hydrogen bonding and sweetness

Abstract

Raman and IR spectra of polycrystalline samples of 4 structurally related sugars, i.e., D-fructose, L-sorbose, 5-deoxy-D-threo-hexulose (5-deoxy-D-fructose) and D-arabinose are reported. Three regions of the spectrum were studied; the OH-stretching region 3650-3100 cm-1, the CH stretching region 3000-2800 cm-1 and the fingerprint region 1600-200 cm-1. Raman spectra in the region 200-10 cm-1 have also been recorded. Bands in the OH stretching region have been correlated with the O-H...O distances obtained from recent neutron diffraction studies. The results are discussed in relation to hydrogen bonding and relative sweetness of these sugars. Detailed assignments are given for the bands in the CH stretching region, and it is shown that the spectra are very sensitive to small structural changes in the molecule. Spectra are presented for the fingerprint region and some characteristic group frequencies are noted for ketohexoses and aldopentoses.