A C-13 AND W-183 NMR-STUDY OF THE STRUCTURES OF TUNGSTATE AND MOLYBDATE COMPLEXES OF VOLEMITOL

H-1, C-13, and W-183 NMR spectroscopic methods were used for the struc tural characterization of the tungstate and molybdate complexes of vol emitol (D-glycero-D-manno-heptitol) in aqueous solution. The major spe cies (type E) are a pair of isomeric complexes formed at the arabino s ite in reversed orientation, i.e., HO-1,2,3,4 and HO-4,3,2,1. A single , minor complex is formed at the HO-3,4,5,6 altro site and is shown to be isostructural with the known single complexes of ribitol and D-alt ritol (type E'). The present NMR results support the hypothesis that c omplexes of type E' are weaker than those of type E because they are d estabilized by a steric strain due to the interaction of the side chai n of the ligand with the site of chelation.