Isomeric equilibria of monosaccharides in solution. Influence of solvent and temperature
Abstract
The compositions of equilibrium mixtures of D-glucose, D-ribose, β-methyl glucopyranoside and β-methyl ribopyranoside in D2O and dimethyl sulphoxide-d6 have been determined by 1H n.m.r. spectroscopy over the temperature range 0–90 °C in terms of the coexisting anomers, tautomers and conformers. In glucose solutions only 4C1 pyranose forms could be detected, but the temperature dependence of the α/β ratio differs in the two solvents. Ribose solutions consist of mixtures of six species, the relative concentrations of which display complex temperature dependences. The experimental results are discussed in terms of solvation contributions to the relative free energies of the different species.