AROMATIC AROMATIC INTERACTIONS - FREE-ENERGY PROFILES FOR THE BENZENE DIMER IN WATER, CHLOROFORM, AND LIQUID BENZENE

An all-atom model for benzene is reported and tested largely in Monte Carlo simulations of pure liquid benzene, benzene in dilute aqueous solution, and the benzene dimer in water and chloroform. Free energy profiles were obtained for the association of the benzene dimer in liquid benzene, water, and chloroform that characterize the energetics for this prototypical interaction between arenes in solution. In all cases a contact dimer with a ring center-ring center separation of ca. 5.5 Å is found to be energetically preferred. Face-to-face stacked structures are net repulsive. However, gas-phase optimizations indicate that shifted, stacked structures become increasingly favorable with increasing arene size. Comparisons are made with key experimental data, including the free energy of hydration of benzene and the association constant, Ka, for the benzene dimer in water. The agreement with the results from the new potential function provides a basis for confidence in the accompanying insights of relevance to molecular design. © 1990, American Chemical Society. All rights reserved.