2004 Volume 77 Issue 4 Pages 651-659
Molecular dianions/dications of many polycyclic aromatic hydrocarbons (PAHs) have long been regarded as antiaromatics because of their global paratropic π-electron current. However, many of them are supposed to be aromatic due to their positive topological resonance energies (TREs). In order to reconcile such energetic and magnetic criteria of aromaticity, we derived a new TRE-like energetic quantity from the magnetic response of the π-system and called it a magnetic resonance energy (MRE). MRE was found to be highly correlative with TRE for a variety of PAHs and their molecular dianions/dications. We can now discuss energetic and magnetic criteria of aromaticity unambiguously on this theoretical basis. Many PAH dianions/dications indeed turned out to be aromatic with positive MREs even if they exhibit paratropic currents along the periphery of the π-system.
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