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Crystal and molecular structure of methyl α-d-galactopyranoside 4-(sodium sulphate) dihydrate

✍ Scribed by Jan A. Kanters; Berend van Dijk; Jan Kroon

Publisher
Elsevier Science
Year
1991
Tongue
English
Weight
663 KB
Volume
212
Category
Article
ISSN
0008-6215

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✦ Synopsis

The crystal and molecular structure of methyl a-n-galactopyranoside C(sodium sulphate) dihydrate has been determined by X-ray analysis at -173". The sugar ring has a distorted 'C, chair conformation. The conformation of the CH,OH group is gauche-trans and the bridging S-O bond is eclipsed with the C-4-H bond, which diminishes the steric repulsion of the sulphate group with the neighbouring CH,OH and HO-3 groups. The sodium ions occupy special positions on two-fold axes and each is co-ordinated six-fold. The three independent oxygen atoms around Na-1 belong to two different sulphate oxygen atoms that are associated with two different sugar rings and O-3 of one of these rings. In the co-ordination of Na-2, the three independent oxygen atoms belong to one of the water molecules and one sulphate group. The co-ordination of Na-1 approaches ideal octahedral symmetry, whereas that of Na-2 is distorted appreciably. Both the co-ordination and hydrogen bonding result in a complex packing pattern in which the single hydrogenbonded helix around the screw is axis involves the hydroxymethyl group and a water molecule, and is almost identical to the arrangement observed for methyl or-D-galactopyranoside monohydrate.

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