THE CRYSTAL AND MOLECULAR-STRUCTURE OF OPROPYLIDENE-ALPHA-D-XYLO-PENTODIALDO-1,4-FURANOSE - A DIMERIC FORM IN THE CRYSTALLINE STATE

isopropylidene-alpha-D-xylo-pentodial-1,4-furanose (1), C16H24O10, M(r ) = 376.4, is orthorhombic, space group P2(1)2(1)2(1) with a = 10.3028 (10), b = 11.1875(3), c = 15.7484(13) Angstrom, V= 1815.2(4) Angstrom( 3), D-c = 1.377 gcm(-3), mu(CuK alpha) = 9.5 cm(-1) and Z = 4. The str ucture was refined to R = 0.033 and R(w) = 0.045 for 1984 observed ref lections. Crystalline 1 has a dimeric cyclic acetal-hemiacetal structu re, formed by self aldol condensation of two monomers. The absolute co nfiguration at the condensation centers, C-5 and C-5', were assigned a s 5R and 5S, respectively. In the dimer 1, the xylofuranose rings adop t different conformations, one is a twist T-3(4), whereas the second i s an envelope E(4) slightly distorted towards the T-3(4) conformation; their fused 1,2-O-isopropylidene rings adopt (O-2)E and T-O-2(C-6) co nformations, respectively. The 1,3-dioxane ring has a distorted chair conformation with puckering parameters Q = 0.516 Angstrom, phi = 90.9, and theta = 11.0 degrees. The molecules are linked in the crystal thr ough intermolecular hydrogen-bonding interactions that involve the two hydroxyl groups, OH-3 and OH-5', and the isopropylidene ring oxygen a toms, O-2 and O-1', as donor and acceptor, respectively.