Nuclear magnetic resonance and conformational studies on monoacetylated methyl D-gluco- and D-galacto-pyranosides

Abstract

¹ H and ¹³C N.m.r. spectra for all mono-O-acetyiated methyl α- and β-glycopyranosides of D-glucose and D-galactose were obtained and compared with those of the corresponding non-acetylated derivatives. It is shown that the ¹³C n.m.r. chemical shifts of the carbons in positions α and β to an O-acetyl group can be approximated using simple rules, for which the number and location of eventual axial substituents are essential. The chemical shifts of the α- and β-protons are in the same way sensitive to axial substituents. Furthermore the conformation of the O-acetyl group was assessed by measurements of ³J_C,C and ³J_C,H of some selected O-acetates, ¹³C-enriched in the carbonyl carbon, and by theoretical energy calculations.