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 isomers have been determined by X‐ray analysis and in situ crystallisation techniques. Attempts to predict these structures in advance by force‐field calculations were not successful, although the known crystal structures of two of the three polymorphs of the 1,4‐isomer were successfully `a posteriori' predicted. Calculated lattice energies were supplemented with estimated lattice‐vibrational entropies obtained in the rigid‐body approximation. Energy calculations for actual and virtual crystal structures indicate that the higher melting point of the 1,4‐isomer can be largely attributed to more efficient crystal packing.