Abstract
Motion and disorder in the crystal structures of benzene, (D~6~)benzene, and the clathrate C~60~⋅(HQ)~3~ (HQ=hydroquinone=benzene‐1,4‐diol) are studied. The observed temperature evolution of their atomic displacement parameters (ADPs) is analyzed in terms of a physical model that explicitly accounts for effects of temperature. The major part of the ADPs of (D~6~)benzene is explained by rigid‐body normal modes. The small but significant fraction that remains is shown to be due to zero‐point intramolecular motion. Comparison of the ADPs of D‐ and H‐isotopomers of benzene confirms the expected isotopic relationship. These findings, which leave no room for disorder between two Kekulé structures, corroborate the validity of the physical model. An analogous treatment of the ADPs of the hydroquinone part of the clathrate compound reveals a distinctive disposition of displacements related neither to rigid‐body nor to zero‐point motion. The pattern is interpreted nearly quantitatively in terms of orientational and positional disorder of the hydroquinone molecule amounting to a few degrees and hundredths of an Ångström, respectively. The model of disorder accounts for unusual bond angles in the average structure and suggests a chemically sensible pattern of locally ordered H‐bonds.