Hydrogen bonds orientational order

The crystal stmcture of PPT is pseudo-orthorhombic (essentially monoclinic) with a = 0.785/nm b = 0.515/nm c (fiber axis) = 1.28/nm and d = 90°. The molecules are arranged in parallel hydrogen-bonded sheets. There are two chains in a unit cell and the theoretical crystal density is 1.48 g/cm. The observed fiber density is 1.45 g/cm. An interesting property of the dry jet-wet spun fibers is the lateral crystalline order. Based on electron microscopy studies of peeled sections of Kevlar-49, the supramolecular stmcture consists of radially oriented crystaUites. The fiber contains a pleated stmcture along the fiber axis, with a periodicity of 500—600 nm. 

Trouton s rule is obeyed most closely by liquids that do not have a high degree of order within the liquid. In both HF and CH3OH, hydrogen bonds create considerable order within the liquid. In C6H5CH3, the only attractive forces are non-directional London forces, which cause the molecules to attract each other, but have no preferred orientation as... 

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