CONFORMATIONAL EQUILIBRIA OF METHYL ALPHA-L-ARABINOPYRANOSIDES IN SOLUTION

Experimental NMR studies on methyl alpha-L-arabinopyranosides in CDCl3 , pyridine and dioxane have shown that the equilibria between conforme rs are displaced in favour of the C-4(1) conformer, except in the case of 2-substituted derivatives in CDCl3. The experimental data and a th eoretical analysis aimed at explaining them in terms of intramolecular and stereoelectronic solvent effects are presented. It appears that c ertain electrostatic interactions and the anomeric effect, which favou r C-1(4) in conformational equilibria are particularly important in 2- substituted derivatives provided no disruption of intramolecular II-br idges takes place, This explains the experimental findings and throws further light on the interplay of effects which determine conformation al equilibria in solution.