Conformations of septanosides. The crystal and molecular structure of 5-O-(chloroacetyl)-1,2:3,4-di-O-isopropylidene-α-D-glucoseptanose

摘要: Abstract The crystal structure of 5-O-(chloroacetyl)-1,2:3,4-di-O-isopropylidene-α- D -glucoseptanose, a seven-membered ring sugar, has been determined by using 1234 reflections measured on diffractometer. crystals belong to the orthorhombic space group P212121, having cell dimensions  27.750, b 10.714, and c 5.702 A. calculated densities are 1.25 g.cm−3 1.32 g.cm−3, respectively; latter value assumed four molecules in unit cell. was combination heavy-atom technique tangent method. Full-matrix least-squares refinement with anisotropic temperature factors for nonhydrogen atoms isotropic hydrogen lowered conventional R 0.066. adopts 5.6C2( ) twist-chair conformation. Both dioxolane rings have envelope shape, puckered being C-2 C-4 ring. molecular packing is dominated Van der Waals forces. conformations three known 7-membered sugars compared. It found that pseudorotation septanose correlated position attachment central