Knowledge Bank

The various crystal structures of inositol isomers must result from the specific orientations of inter-associating hydrogen bonds. Myo-inositol is comprised of one polar and five equatorial hydroxyls on a cyclohexane ring in a chair conformation. If the polar hydroxyls are bonded to diametrically opposite hydroxyls in adjacent molecules, the other four participate in polymers describing the b-axis of the crystal; the resulting unit cell, is monoclinic with the dimensions and symmetry properties reported by White (1a). In the dihydrate the b-axis is increased (1b), probably by the insertion of water molecules. The infrared spectra using the material in KBr pellets will be reported for the $4000-350cm-1$ region. In that of dry myo-inositol OH \ldots O stretching frequencies appear at 3380 and $3230cm-1$, the former ascribable to the polar-equatorial bond and the latter to the equatorial-equatorial bonds along the b-axis. In the dihydrate the latter is shifted to about $3400cm-1$. Deformation frequencies are also effected by hydration. The crystal structure of cis-inositol, isolated by Angyal et al. (2), has not been reported in the literature. This isomer is comprised of three polar intra-associated hydroxyls on alternate sites of the cyclochexane ring. The other three hydroxyls occupying equatorial sites. It seems likely that pairs of adjacent molecules are inter-associated by two dimers and that these are forced by steric conditions into hexagonal patterns, each molecule participating in three hexamers except on the periphery of the crystal. The spectra show OH \ldots O stretching frequencies at about 3425, 3360 and $3280cm-1$, ascribable to the intra-associated triols formed by the polar units, to the internal hexamers, and to the peripheral dimers of the inter-associated equatorial units, respectively. Such inter-associated molecules would form either hexagonal or more probably diamond-like crystals.