The infrared spectra of crystalline polysaccharides. VIII. Xylans

Abstract Oriented films of 4‐ O ‐methylglucuronoxylan from several sources were prepared by hot stretching acetyl derivatives. The resulting oriented samples could be converted to crystalline xylans without destroying the orientation. Infrared spectra of the oriented samples were recorded using polarized radiation. Band assignments were made on the basis of empirically known group frequencies, the spectra of the deuterated analogs (OH → OD), and comparison with the spectra of small molecule model compounds. The dichroic ratios observed for the carbon hydrogen modes in the polarized spectrum along with the observed 15 A. fiber repeat of crystalline xylan “hydrate” are interpreted in terms of a threefold screw polymer conformation. Finally, by comparison of the polarized spectrum of an oriented hardwood xylan with that derived from a radial section of hardwood it was deduced that the xylan is oriented in the fiber direction in the tree.