Benzene, aromatic rings, van der Waals molecules, and crystals of aromatic molecules in molecular mechanics (MM3)

Benzene has been studied with the MM3 force field, first as a monomer, then as a van der Waals dimer, then in the crystal. The non‐bonded aromatic portion of the MM3 force field has been derived to fit reasonably well the known properties for the above. The force field includes dipoles of 0.6 and 0.9 D for C H and C C bonds, respectively. The benzene dimer is calculated to have a lower energy when perpendicular, than when eclipsed face to face. The crystal of benzene has a herringbone pattern with correct cell constants and heat of sublimation, while hexamethylbenzene as the dimer and in the crystal has a skewed‐stack of pancakes type structure, as observed.