Vacancy Formation Process Research Articles

X-ray Investigation of Some Plastic Crystals II. Density of Vacancies in Cyclohexane, Cyclohexanol and dl-Camphene

X-ray powder photographs are used to calculate cell parameters for cyclohexane, cyclohexanol, and dl-camphene for a wide range of temperature. Comparison with the ordianary bulk density of cyclohexane and cyclohexanol leads to upper limits for the vacancy concentrations in these substances of 0.5% and 0.3%, respectively. Above about 10 °C the bulk density of camphene falls off markedly form what would be expected on the basis of the cell parameters. Comparison of the densities at higher temperatures with those to be expected either on the basis of the X-ray data or on the basis of linear extrapolation of the densities at lower temperatures leads to ΔH = 12.5 ± 0.5 kcal/mol and ΔS = 35 ± 2 e.u./mol for the process of vacancy formation. This value for the entropy implies that about 15 molecules gain additional freedom of motion every time one vacancy is formed. These results lead to predictions for the temperature variation in the ratio of molecular scattering factors for the 110 and 200 lines of camphene that are consistent with the observed ratios.