From this analysis we conclude that π-stacking is unique among other dispersion-driven interactions, specifically due to the planarity of the arene moiety that facilitates exceptionally strong interactions when two arenes are arranged in a cofacial geometry but considerably weaker interactions (at least for PAHs) in the T-shaped geometry. The difference is that the cofacial arrangement allows for closer approach of the two arenes, which can then access short-range electrostatic interactions which are attractive in the cofacial geometry. Thus, the fact that exact electrostatics differs in sign from quadrupolar electrostatics for cofacial arenes is, in fact, a crucial aspect of what makes π-stacking special, different from ordinary dispersion interactions. Two arenes in a T-shaped geometry still interact via dispersion forces but are kept farther apart due to Pauli repulsion of the C-H• • • π arrangement and do not access the attractive short-range electrostatic interaction, leading to systematically weaker interaction energies as compared to those in cofacial geometries. Interactions in [n]graphane models are weaker for the same reason.