Conformational equilibria of methyl α-L-arabinopyranosides in solution

Abstract

Experimental NMR studies on methyl α-L-arabinopyranosides in CDCl₃, pyridine and dioxane have shown that the equilibria between conformers are displaced in favour of the ⁴C₁ conformer, except in the case of 2-substituted derivatives in CDCl₃. 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 ¹C₄ 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.