Note that this explanation for what is special about π-stacking invokes planarity but not aromaticity. The former obviously derives from the latter, yet our analysis suggests that exceptionally strong stacking interactions should be available to systems that are planar but not aromatic. In fact, this has been observed. Our mental image is that the dispersion interactions associated with the π-electron density (or some otherwise planar moiety) are served up on a two-dimensional platter, resembling a pizza peel, which can be rotated into an optimal coplanar configuration but whose shape cannot be deformed. If it can be, as in the perhydroacenes, then the stronger stacking interactions are lost. We refer to this as the "pizza-π" model of stacking interactions. 148 Strong π-π interactions turn out to be more about the pizza (molecular planarity) than they are about the π (aromaticity).