Chemistry at the interior atoms of polycyclic aromatic hydrocarbons

For more than 150 years, chemical reactions that make new covalent bonds to polycyclic aromatic hydrocarbons (PAHs) have been confined almost exclusively to substitution and addition reactions on the perimeters of the compounds (edge chemistry). The interior atoms of PAHs, those belonging to three rings, almost never engage in new sigma-bond-forming reactions. A compound with no edges, C-60, was the first polycyclic carbon pi-system observed to exhibit such reactivity. More recently, smaller subunits of C-60, which we call geodesic polyarenes, have also been found to exhibit fullerene-type chemistry at their interior carbon atoms. These reactions are all reviewed together here for the first time. The review ends with speculation that s-bond-forming reactions may also be observed someday even in certain planar, benzenoid PAHs, although no examples have yet been reported.