Anion-molecule complexes in solution. II. The complexing of halide ions with acetylated β-D-glucopyranosyl derivatives

Tetra-O-acetyl-β-D-glucopyranosyl halides and phenoxides in solution in acetonitrile showed a specific deshielding of H-1, H-3, and H-5 on addition of tetraethylammonium halides. The shifts and equilibrium constants increased as the anion radius decreased. The ortho hydrogens of the phenoxide aglucons were also significantly deshielded. The strong dependence of the equilibrium constants of the phenoxide compounds on p-substituents indicated considerable involvement of the phenyl groups in a specific conformation. A simple electrostatic model was successful in correlating the energies and predicting the structures of the complexes. It was not necessary to postulate specific hydrogen bonding to account for association of the anion with an electrophilic region of the molecule. The calculations required specific orientations of acetoxy groups with respect to the pyranose ring which are consistent with those of related studies. In favorable circumstances, the method may be used as a probe for electrophilic regions in molecules.