Entropy and Molecular Motion in the Condensed Phases of Tetrahedral Molecules

By a comparison of the entropies of sublimation at the triple points of carbon tetrafluoride, carbon tetrachloride and neopentane with those of inert gas solids, it has been shown that these molecules are in the state of hindered rotation rather than of reorientation in the solid at the respective triple points, with heights of the potential barrier of 1.0, 2.4 and 1.3 kcal./mol. respectively. The hindering potential has been shown to be proportional to the transition temperatures of these solids. A simple model for the structure of liquid carbon tetrachloride has been presented to account for its entropy of vaporization; the model consists in assuming nearest neighbor crystallite embryos in the liquid.