Conformational equilibria of methyl [small alpha]-L-arabinopyranosides in solution

Experimental NMR studies on methyl [small alpha]--arabinopyranosides in CDCl{,} pyridine and dioxane have shown that the equilibria between conformers are displaced in favour of the conformer{,} except in the case of 2-substituted derivatives in CDCl. The experimental data and a theoretical analysis aimed at explaining them in terms of intramolecular and stereoelectronic solvent effects are presented. It appears that certain electrostatic interactions and the anomeric effect{,} which favour in conformational equilibria are particularly important in 2-substituted derivatives provided no disruption of intramolecular H-bridges takes place. This explains the experimental findings and throws further light on the interplay of effects which determine conformational equilibria in solution.