Structure-property relationships of molecular shape and orientation with compression and expansion of xylitol.

Easy crystallization distinguishes xylitol from other sugars, which usually condense into a syrup from aqueous solution. Although two polymorphs, i.e. metastable monoclinic and high-density orthorhombic, have been reported for xylitol, only the latter is in practical use. Under high pressure, the same orthorhombic phase has been obtained by both isothermal and isochoric recrystallization. The stability of the orthorhombic xylitol phase to 5.0 GPa has been correlated with a uniform compression of all hydrogen bonds and some flexibility of the molecular conformation, which cushion the pressure-induced local strains. The anisotropic compressibility of xylitol and its thermal expansion are consistent with the rule of inverse effects of pressure and temperature. This inverse strain relationship has been correlated with the dimensions and orientation of xylitol molecules in the crystal structure.