Unexpected Substituent Effects in Face-to-Face π-Stacking Interactions

State-of-the-art electronic structure methods have been applied to obtain the first high-quality theoretical results for substituent effects in π-stacking interactions. The sandwich configurations of benzene dimer, benzene−phenol, benzene−toluene, benzene−fluorobenzene, and benzene−benzonitrile have been studied using correlation consistent basis sets augmented by multiple diffuse functions, namely aug-cc-pVDZ and aug-cc-pVTZ, at the second-order perturbation theory (MP2) level. Coupled-cluster computations with perturbative triples [CCSD(T)] were performed and combined with the above MP2 calculations to estimate the CCSD(T)/aug-cc-pVTZ binding energies, which should be accurate within several tenths of a kcal mol-1. All substituted dimers bind more strongly than benzene dimer, with benzene−benzonitrile binding the most strongly. Both electrostatic and dispersion interactions contribute to the increased binding of the monosubstituted dimers.