Conformations of the Pyranoid Sugars. II. Infrared Absorption Spectra of Some Aldopyranosides

The conformations of twenty-four aldopyranosides have been studied by analysis of their infrared absorption spectra. The most stable conformations of twelve of the glycosides had previously been assigned by Reeves from a study of their instability factors; these conformations were assumed to apply to the crystalline state, for which the spectra had been recorded. The compounds were classified into (a) configurationally and (b) structurally related groups, and the spectra were intercompared. The analysis revealed groups of absorption bands which showed a concerted shift on change of anomeric disposition. With these groups of absorption bands thus identified, intercomparison with nine of the remaining spectra afforded evidence that the anomeric group (1) is axial in methyl d-glycero-α-l-gluco-heptopyranoside, methyl d-glycero-α-l-manno-heptopyranoside, and methyl d-glycero-α-d-gulo-heptopyranoside; (2) is equatorial in methyl 6-deoxy-β-l-mannopyranoside, methyl d-glycero-β-d-gulo-heptopyranoside, and cyclohexyl d-glycero-β-d-gulo-heptopyrnoside; and (3) either is quasi or occurs as different (or mixed) axial and equatorial forms in methyl α-d-lyxopranoside, methyl β-d-lyxopranoside, and (possibly) α-d-methylgulopyranoside. Three of the glycosides were available as their crystalline complexes with calcium chloride. The spectra of these complexes were also examined, and the effect of co-crystallization with calcium chloride is pointed out.