X-ray analysis of complex crystal structures: α- rhamnose monohydrate
McGeachin, Hugh McDougall
The crystal structure Of α-rhamnose monohydrate has been determined by the interpretation of the three dimensional Patterson function, and refined on two projections using diffraction data derived from Geiger counter measurements. There are possibly significant deviations from the expected values of three bond lengths, which include both the axial C-OH bonds of the molecule, one of which is short, as in α-glucose, and the other long. There are several significant deviations from the tetrahedral angle in the bond angles; that at the oxygen atom of the ring is 120° and those made by the extracyclic substituents appear to indicate a repulsion between them. The crystal packing is determined by hydrogen bonds, in which all the oxygen atoms and the water molecule take part, and in which all the available hydrogen atoms are utilised. The hydrogen atoms appear with moderate definition on (F0 - Fc) syntheses but their positions are not completely unambiguous largely owing to the non-centrosymmetrical nature of the crystal, the poor resolution of the atoms in projection and the occurrence of anisotropic thermal vibrations of the atoms, for which no corrections were made.