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Methyl [beta]-D-galactopyranosyl-(1[rightwards arrow]4)-[beta]-D-xylopyran­oside, C12H22O10, (II), crystallizes as colorless needles from water with positional disorder in the xylopyranosyl (Xyl) ring and no water mol­ecules in the unit cell. The inter­nal glycosidic linkage conformation in (II) is characterized by a [varphi]' torsion angle (C2'Gal-C1'Gal-O1'Gal-C4Xyl) of 156.4 (5)° and a [psi]' torsion angle (C1'Gal-O1'Gal-C4Xyl-C3Xyl) of 94.0 (11)°, where the ring atom numbering conforms to the convention in which C1 denotes the anomeric C atom, and C5 and C6 denote the hy­droxy­methyl (-CH2OH) C atoms in the [beta]-Xyl and [beta]-Gal residues, respectively. By comparison, the inter­nal linkage conformation in the crystal structure of the structurally related disaccharide, methyl [beta]-lactoside [methyl [beta]-D-galactopyrano­syl-(1[rightwards arrow]4)-[beta]-D-glucopyran­oside], (III) [Stenutz, Shang & Serianni (1999). Acta Cryst. C55, 1719-1721], is characterized by [varphi]' = 153.8 (2)° and [psi]' = 78.4 (2)°. A comparison of [beta]-(1[rightwards arrow]4)-linked disaccharides shows considerable variability in both [varphi]' and [psi]', with the range in the latter (~38°) greater than that in the former (~28°). Inter-residue hydrogen bonding is observed between atoms O3Xyl and O5'Gal in the crystal structure of (II), analogous to the inter-residue hydrogen bond detected between atoms O3Glc and O5'Gal in (III). The exocyclic hy­droxy­methyl conformations in the Gal residues of (II) and (III) are identical (gauche-trans conformer).
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