VIBRATIONAL-SPECTRA AND STEREOISOMERISM OF THE HEXOPYRANOSE RING IN EPOXYSACCHARIDES

Investigation of the potential surface of methyl 3-anhydro-2,3,4-tride oxy-beta-D-lyxohexopyranoside has shown that the molecule has seven co nformers with different frameworks. A comparative analysis of the calc ulated frequencies, forms, and FED of normal vibrations of the seven c onformers allowed us to follow the frequency shifts of similar modes, which depend on the geometry of the epoxysaccharide framework. In the high-frequency region of the vibration spectrum, FED has considerable contributions from the deformation vibrations of methine and methylene (CCH, OCH) groups, and we can clearly observe a dependence of the fre quency shift on the geometry of the ring at the site where vibrating g roups are localized. The vibrations that have predominant contribution s to FED from the C-O stretching vibrations depend on the overall geom etry of the molecule. In the low-frequency region (below 700 cm(-1)), skeletal deformation modes appear. Apart from the common dominant form s of vibrations, each conformer is characterized by individual ''devia tions'' that depend on the conformation of the hexopyranose ring as a whole. The frequency shifts in this case can be 100 cm(-1) or higher.