Monosaccharides, hydrogen bonding

The structures of two (p-bromophenyl)hydrazones have been determined from projection data. The first was that of D-ribose,112 in which the D-ribose is acyclic, in a sickle18 conformation, and C-l, C-2, C-3, and C-4 are coplanar. Rotation of C-5 out of this plane relieves the 0-2, 0-4 interaction that would be present in the extended conformation and brings 0-5 close to 0-2, so that an intramolecular hydrogen-bond can be formed this is the first (and, thus far, the only) case of an intramolecular hydrogen bond in a crystal of a monosaccharide derivative. The hydroxyl groups on C-2, C-3, and C-4 form three intermolecular hydrogen-bonds. 

Intramolecular hydrogen-bonding between two oxygen atoms in the same monosaccharide is of minor importance in a crystal lattice. Only one example is at present known, namely, in D-ribose (p-bromo-phenyl)hydrazone.l,z... 

A notable feature of carbohydrate crystals is the absence (or small proportion) of water of hydration. As monosaccharides are hydrophilic and water-soluble, considerable deposition of water (association) in a sugar crystal may be expected. The absence of water from the crystal lattice of a sugar must, therefore, be explained by supposing that the sugar is able to form sufficiently strong and numerous hydrogen bonds without the involvement of molecules of water this has been observed, although there are some exceptions. 

---