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.