The beta-pyranose form, (III), of 3-deoxy-D-ribo-hexose (3-deoxy-D-glucose), C(6)H(12)O(5), crystallizes from water at 298 K in a slightly distorted (4)C(1) chair conformation. Structural analyses of (III), beta-D-glucopyranose, (IV), and 2-deoxy-beta-D-arabino-hexopyranose (2-deoxy-beta-D-glucopyranose), (V), show significantly different C-O bond torsions involving the anomeric carbon, with the H-C-O-H torsion angle approaching an eclipsed conformation in (III) (-10.9 degrees ) compared with 32.8 and 32.5 degrees in (IV) and (V), respectively. Ring carbon deoxygenation significantly affects the endo- and exocyclic C-C and C-O bond lengths throughout the pyranose ring, with longer bonds generally observed in the monodeoxygenated species (III) and (V) compared with (IV). These structural changes are attributed to differences in exocyclic C-O bond conformations and/or hydrogen-bonding patterns superimposed on the direct (intrinsic) effect of monodeoxygenation. The exocyclic hydroxymethyl conformation in (III) (gt) differs from that observed in (IV) and (V) (gg).