Solid-state behaviour of the dichlorobenzenes: Actual, semi-virtual and virtual crystallography

The crystal structures of the low-melting 1,2- and 1,3-dichlorobenzene isom ers have been determined by Xray analysis and in situ crystallisation techn iques. Attempts to predict these structures in advance by force-field calcu lations were not successful, although the known crystal structures of two o f the three polymorphs of the 1,4-isomer were successfully 'a posteriori' p redicted. Calculated lattice energies were supplemented with estimated latt ice-vibrational entropies obtained in the rigid-body approximation, Energy calculations for actual and virtual crystal structures indicate that the hi gher melting point of the 1,4-isomer can be largely attributed to more effi cient crystal packing.