The crystal structure of 5-O-Acetyl-1,2 : 3,4-di-O-isopropylidene-α-D-glucoseptanose, C₁₄H₂₂O₇, by use of X-ray and neutrondiffraction data

Abstract

The crystal structure of 5-O-acetyl-1,2:3,4-di-O-isopropylidene-α-D-glucoseptanose [P2₁2₁2₁, Z 8, a 14.329(5), b 22.075(5), c 10.012(5) Å] has been determined by X-ray and neutron diffraction analyses. For the neutron diffraction analysis, the acetate group and the trans-O-isopropylidene group were deuterated. Constrained refinement was used in the neutron diffraction analysis to counter over parameterization in the block-diagonal least-squares refinement. Final unweighted R-values were 0.038 [X-ray for 3070 reflections with [F_o > 2.58σ (F_o)] and 0.061 [neutron for 1118 reflections with F_o > 4σ ([F_o)]The neutron refinement revealed a disordering of the acetate methyl group in each of the two independent molecules in the asymmetric unit. The septanose ring in each molecule adopted the same twist-chair conformation but the dioxolan rings assumed different twist and envelope conformations.