Face-to-Face Arene-Arene Binding Energies: Dominated by Dispersion but Predicted by Electrostatic and Dispersion/Polarizability Substituent Constants

Parallel face-to-face arene arene complexes between benzene and substituted benzenes have been investigated at the MP2(full)/6-311G** and M05-2X/6-311G** levels of theory. A reasonably good correlation was found between the binding energies and the Sigma vertical bar sigma(m)vertical bar values of the substituted aromatics. It is proposed that a substituent vertical bar sigma(m)vertical bar value informs on both the aromatic substituent dispersion/polarizability and the effect the substituent has on the aromatic electrostatics. Supporting this hypothesis, a combination of electrostatic (Sigma sigma(m)) and dispersion/polarizability (Sigma M-r) substituent constant terms gives an excellent, and statistically significant, correlation with the benzene-substituted benzene binding energy. Symmetry adapted perturbation theory energy decomposition calculations show the dominant attractive force is dispersion; however, the sum of all nonelectrostatic forces is essentially a constant, while the electrostatic component varies significantly. This explains the importance of including an electrostatic term when predicting benzene-substituted benzene binding energies.