POLARIZED FT-IR AND RAMAN-SPECTRA OF BETA-D-FRUCTOPYRANOSE SINGLE-CRYSTALS

Polarised FT-IR and Raman spectra have been recorded for beta-D-fructopyranose single-crystal samples at room temperature. The assignment of absorption bands to the stretching (nu(OH)) and out-of-plane bending (gamma(OH)) vibrations of the hydrogen-bonded OH groups is proposed on the basis of the 'oriented gas' model approximation. For the very weak H-bond the transition dipole moment is located in the direction of the O-H bond whereas it lies in the O...O direction for the stronger H-bond, O(2)-H...O(1). Different couplings between the nu(OH) vibrations are discussed and proposed based on polarised spectra. Assignment is made of the stretching vibrations of the CH2 and CH groups. Other vibrations appear to be mixed and very complex. Only a tentative assignment for the C-O stretching vibrations is proposed.