We present ab initio quantum-chemical calculations including correlation effects via second-order Møller-Plesset perturbation theory, of the structures of the complexes that benzene forms with water, ammonia, methane, and formic acid, and of the pyrene-water complex. We describe our results for a number of complex structures, including symmetric and nonsymmetric configurations, in which the aromatic molecule acts as proton acceptor. In some instances, configurations where benzene is the proton donor are also investigated. Series of calculations are performed in order to assess the energy required for the Lewis acid molecule to move on top of benzene or pyrene. Our results are compared to available experimental data on the geometries and relative binding energies of these complexes. © 1989 American Institute of Physics.