Aromaticity Evaluations of Planar [6]Radialenes

The aromatic character of fused polycyclic systems varies with the nature of their annulated rings. Computed extra cyclic resonance energies (ECREs) reveal that the central six membered rings (6MRs) of the heterocyclic fused congeners 1-5 are "[6]radialene-like", but that the central 6MRs of triphenylene 9, coronene 10, and isocoronene 11 are "benzene-like." Comparisons with geometric (harmonic oscillator model of aromaticity, HOMA) and magnetic (nucleus independent chemical shifts, NICS) criteria illustrate the multifaceted nature of aromaticity in 1-11.