X-ray Investigation of Some Plastic Crystals I. Structure and Rotation: Cyclopentanol and dl-Camphene

AbstractX-ray photographs have been made of the two rotational forms of solid cyclopentanol and of the rotational form of dl-camphene. At −30°C, cyclopentanol in rotational form I has a hexagonal structure with a = 5.877 Å and c = 1.607 Å and with two molecules per cell. Agreement with the observed intensities can be obtained by assuming that the molecules are located at (1/3, 2/3, 1/4) and (2/3, 1/3, 3/4) and that they are rotating with spherical symmetry about their centers of mass. At −56°C, cyclopentanol in rotational form II also has a hexagonal structure but with a = 10.1 Å and c = 9.49 Å and with six molecules per cell. Intensity ratios are used to find the ratios of molecular scattering factors for camphene at six temperatures between −83.1° and + 24.0°. A model in which the camphene molecules rotate about their centers of mass with spherical symmetry does not produce agreement with the observed results. A model in which the camphene molecules fluctuate randomly among the twelve positions that result from applying the minimum symmetry operations for the point group in cubic lattice (class 23 or T) can be used to obtain agreement with the observed ratios.