Substituent Effects in π−π Interactions:  Sandwich and T-Shaped Configurations

Sandwich and T-shaped configurations of benzene dimer, benzene−phenol, benzene−toluene, benzene−fluorobenzene, and benzene−benzonitrile are studied by coupled-cluster theory to elucidate how substituents tune π−π interactions. All substituted sandwich dimers bind more strongly than benzene dimer, whereas the T-shaped configurations bind more or less favorably depending on the substituent. Symmetry-adapted perturbation theory (SAPT) indicates that electrostatic, dispersion, induction, and exchange-repulsion contributions are all significant to the overall binding energies, and all but induction are important in determining relative energies. Models of π-π interactions based solely on electrostatics, such as the Hunter-Sanders rules, do not seem capable of explaining the energetic ordering of the dimers considered.