Ahatraet
-The infrared spectra of a-and B-o-galactose were recorded, both in the mid-IR range (4000-5OOcm-r) and in the far-IR (500-50cm-'). The Raman spectra were also obtained. These spectra constitute the basis of a crystalline-state force field established for these two molecules through a normal coordinate analysis. A modified Urey-Bradley-Shimanouchi force field was combined with an intermolecular potential energy function which includes van der Waals interactions, electrostatic terms and an explicit hydrogen bond function. The force constants were varied, so as to obtain an agreement between the observed vibrational frequencies and the calculated ones of a-o-galactose. The force field obtained was then applied to a-o-galactose O-d5 and ,V-o-galactose, in order to test its transferability. The computed potential energy distribution was found to be compatible with previous assignments for o-glucose, particularly for the modes involving C6 and C-OH groups. For B-o-galactose the same force field was used with changing the force constants due to the Cl and C6 groups. THE normal coordinate analyses of the Q-and /?-D-galactose molecules provide a useful approach to the interpretation of the vibrational spectra of the polysaccharides. Indeed, in the spectra of some polygalactanes, such as agar and carageenans, many of the bands in the region below 15OOcm-' are due to mixing of internal coordinates; thus an assignment on the basis of group-frequencies is unsatisfactory. However, certain bands are always present, independent of the substitutions on the pyranose ring. These bands are attributable to skeletal motions of o-galactose [l, 21, but they have never been assigned to specific vibrational modes. Up to the present, some temptations of assignments have been made on the basis of a previous normal coordinate analysis for Dglucose [3-61. Thus, in order to make more precisely some assignments in the polygalactanes spectra, it seems particularly important to extend the analysis and to establish the force field of a common sugar such as o-galactose. EXPERIMENTALMETHODS Samples Commercial o-galactose from Sigma (G0750) was used with the two recrystallization methods described previously by SHELDRICK [7], in order to obtain crystalline powders of Q and B-Dgalactose. The principle is based on their solubility differences in water-ethanol mixtures at high and low temperatures, respectively. After an X-ray examination of the /3-D-galactose powder which was obtained, it was concluded that crystals of the a-anomer were also present. So, the comparison of the spectra of the /?-o-galactose obtained and the pure a-o-galactose, yielded the characteristic bands of the fi-o-galactose. The 0-deuterated o-galactose was obtained by deuterium exchange of a-D-galactose crystals in an excess of DzO. A freeze-drying method permitted the powder consisting of a mixture of the two anomers, primarily a-D-galactose 0-ds, to be obtained.