Relaxed-residue energy maps based on the MM3 force field were computed for the three C-linked (1-1) D-glucosyl disaccharides, C-trehaloses: the axial-axial linked α,α-trehalose, the axial-equatorial α,β-trehalose and the equatorial-equatorial linked β,β-trehalose. Optimized structures were calculated on a 20°-grid spacing of the torsional angles about the C-glycosidic bonds. Boltzman weighted 3J coupling constants were calculated and compared to the experimental values; they are satisfactory. The general shape of the energy maps indicates that α,α-trehalose is a quite rigid molecule adopting only one conformation around the C-glycosidic linkage, whereas the other two isomers are rather flexible. Compared to the corresponding O-disaccharides α,β-and β,β-trehaloses exhibit a larger number of low energy conformers and a larger area of the map energy < 8 kcal/mol. The preferred conformations of the axial C-glycosidic bond are in agreement with the exo-anomeric effect. Equatorial C- glycosidic bonds are rather flexible, influenced by the polarity of the milieu and the formation of interresidue hydrogen bonds
