1,2 : 4,5-Di-O-isopropylidene-beta-D-erythro-hexo-2,3-diulo-2,6-pyranose

The crystal structure of title compound, C12H18O6, has been determined usin g single-crystal data. There are two independent molecules in the asymmetri c unit. NMR coupling constants, dihedral angles as well as puckering parame ters indicate the S-3(0) conformation of the pyranose ring in both molecule s A and B. The cis-fused 1,3-dioxolane ring in both molecules A and B, adop ts an E-4 conformation. The second five-membered 1,3-dioxolane ring, in mol ecule A, has an E-2 conformation, whereas in molecule B, this 1,3-dioxolane ring adopts an E-4 conformation. Molecules A form a zigzag infinite chain along the b axis with molecules B as side chains. This explains why the dis placement ellipsoids of atoms of molecule B are substantially larger than t hose of molecule A.