σ-σ, σ-π, and π-π Stacking Interactions between Six-Membered Cyclic Systems. Dispersion Dominates and Electrostatics Commands

The characteristics of the interaction in aliphatic-aliphatic (sigma-sigma), aliphatic-aromatic (sigma-pi), and aromatic-aromatic (pi-pi) dimers have been studied employing benzene, cyclohexane and some of their fluorinated derivatives. Though fluorination dramatically changes the electrostatic properties of the molecules, the interaction only changes notably when the fluorinated species interacts with a significantly polar molecule. Fluorination hardly affects the interaction with cyclohexane or trifluorobenzene, both with small dipole and quadrupole moments. The results indicate that whereas dispersion constitutes the leading stabilising contribution in most of the dimers considered, it is the electrostatic term the one reflecting the changes on the interaction introduced by fluorination. As a consequence, the order of stability of the complexes studied follows the trends observed for the electrostatic term, despite not being the largest stabilising contribution.