Crystalline modifications of cellulose. Part V. A crystallographic study of ordered molecular arrangements

With the arrangements of molecular chains postulated in Part III as a basis, crystal structures for the ordered regions of ramie and regenerated celluloses have been set up. Comparison of the ( hkl ) x‐ray intensities calculated for cellulose I structures with the measurements reported in Part IV reveals serious discrepancies on the first layer‐line. From extensive calculations over a range of structures, it appears that no conventionally ordered structure built from a P 2 1 unit cell of approximate dimensions 8.2 × 10.3 × 7.9 A., β = 84°, can be expected to yield as weak ( h 1 l ) planes as are observed. An element of randomness in the polarity of the chains would diminish the discrete intensities on the higher layers relative to the ( h 0 l ) reflections and so be more in accord with experiment. For cellulose II, attention was concentrated on antiparallel chain structures with the r shift near 0.29. Although the overall agreement was better than for cellulose I, such structures did not account for the very weak low‐order ( h 1 l ) reflections observed. The disparity was not reduced by types of disordering acceptable on stereochemical and spectroscopic grounds. The major part of the disagreement is tentatively attributed to regarding the observed coherent scattering as emanating from fully ordered unit cells of the accepted dimensions and symmetry, and to neglecting contributions from oriented amorphous regions.