BENZENE, NAPHTHALENE AND ANTHRACENE DIMERS AND THEIR RELATION TO THE OBSERVED CRYSTAL-STRUCTURES

Molecular packing in benzene, naphthalene and anthracene crystals is analyzed in terms of molecular dimer interaction. Intermolecular energies of the gas dimer molecules are calculated for various intermolecular distances and orientations using empirical (exp-6-1) potential-energy functions. The gas dimers are compared to pairs of molecules extracted from the observed crystal structures. Particular attention is given to intermolecular Coulombic interaction. Net atomic charges are obtained by the potential-derived method from 6-31G and 6-31G** level ab initio wavefunctions. In the benzene crystal there are strong edge-plane intermolecular Coulombic interactions. The edge-plane interaction becomes somewhat less important in naphthalene and anthracene and the van der Waals interaction increases in importance.