Schiff bases or glycosylamines: crystal and molecular structures of four derivatives of d-mannose Original Research Article

Crystal and molecular structures of four derivatives of d-mannose are described. Each could exist as either an open-chain Schiff base or as a glycosylamine in the solid state. The derivative formed upon reaction of d-mannose with hydroxylamine is an open-chain oxime, but those formed upon reaction with semicarbazide, aniline, and p-chloroaniline are glycosylamines. The oxime, which crystallizes as the syn-(E) isomer, has a fully extended carbon chain. The glycosylamines are all β-pyranoses. The packing arrangement of the oxime involves ‘head-to-tail’ hydrogen bonding. The semicarbazide derivative, which crystallizes as a dihydrate, features a hydrogen-bonded intramolecular bridge formed by the two water molecules and linking O-6 to the carbonyl oxygen atom. The packing arrangements of the aniline and p-chloroaniline derivatives differ from each other but are nevertheless closely related by similar hydrogen-bonding interactions.