The most stable class of benzenoid hydrocarbons - New topological correlations of strain-free total resonant sextet benzenoids

While briefly reviewing how the concepts of strictly pericondensed, strain-free, Clar's aromatic sextet, and symmetry are interconnected in the topological correspondence between strictly pericondensed and total resonant sextet (TRS) benzenoid hydrocarbons, new structural correlations in isomer numbers, symmetry distributions, and empty rings between various strain-free TRS benzenoids made up of only fused hexagonal rings are presented. These correlations are made evident by the Formula Periodic Table for Total Resonant Sextet Benzenoid Hydrocarbons [Table PAH6(sextet)] and application of the leapfrog operation. A new perimeter topology relationship for fused strain-free TRS benzenoids is derived. This work represents a contribution toward understanding formula/structure relationships of benzenoid hydrocarbons.