Molecular and crystal structure of cellulose acetate dipropanoate (CADP, 6-O-acetyl-2,3-di-O-propanoyl cellulose)

The molecular and crystal structure of cellulose acetate dipropanoate (CADP, 6-O-acetyl-2,3-diO-propanoyl cellulose) has been determined by using a constrained linked-atom least-squares refinement method, combined with X-ray and electron diffractograms and stereochemical refinement. The diffraction analysis indicated that CADP crystallized in a P2₁ monoclinic space group with unit cell parameters:a=1.088 nm,b(unique axis)=1.593 nm,c(fibre axis)=1.509 nm and=94.1°. The best model derived from combining the stereochemical refinement with the diffraction intensities gave R=0.217 (R=0.195) for the three-dimensional information from the X-ray fibre diagram and R=0.198 for the base plane data resulting from electron diffraction analysis. In the model, the crystal structure of CADP consisted of a system of right-handed threefold helices packed in an antiparallel fashion, with two molecules passing through the unit cell.