The strucrure of trans- O-β- D-glucopyranosyl methyl acetoacetate, and the interpretation of its optical rotations

Abstract

Crystal-structure determination of trans- O-β- D-glucopyranosyl methyl acetoacetate, C 11H 18O 8, m.p. 186°, confirmed the trans orientation deduced previously from physical properties. The conformation of the D-glucopyranosyl group is 4 C 1, although the most symmetrical chair-conformer is actually 3C o. The glycosidic link is  sc, with a CO anomeric bond of 1.428 Å (142.8 pm), i.e. longer than is normal in methyl β-glycopyranosides. All of the hydrogen bonding is intermolecular. The unusual optical rotations in solution can be interpreted in terms of rotameric populations that are derived from the solid-state conformers and are stabilized by intramolecular or solvent hydrogen-bonding.