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Order-disorder transitions in 1-and 2-methyladamantane, 1,3-dimethyladamantane, 1,3,5trimethyladamantane, 1,3,5,7-tetramethyladamantane and in the I-halogenoadamantanes have been investigated by differential scanning calorimetry. The effects of substituent groups on the disordered phase behaviour of these molecules are discussed.

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The results of differential scanning calorimetry studies on caged hydrocarbons have been used, with existing data, to propose a new interpretation of orientational disorder in plastic crystals. New empirical relationships are reported between the entropy of transition, plastic crystal range and molecular shaDe.

Electron diffraction measurements on germanium tetrafluoride gas are described, and a value of 1-67 f 0.03 for the germanium-fluorine distance is reported. This value is smaller than that predicted by the covalent radii additivity rule, and the contraction is compared with those shown by bonds between fluorine and certain other elements in the first three rows of the periodic table. Deviations from the Schomaker-Stevenson rule are considered.All of the fluorides of Group IV, V and VI elements in the first three rows of the periodic table, except germanium tetrafluoride, have been studied previously by electron diffracti0n.l The bond lengths between the fluorine and central atoms in these compounds show interesting trends, so a determination of the Ge-F distance in germanium tetrafluoride was carried out to fill the gap.