title: Valence-bond determination of diradical character of polycyclic aromatic hydrocarbons: from acenes to rectangular benzenoids.
abstract: The number of Kekulé resonance structures in a conjugated hydrocarbon is a measure of its singlet ground state, and its number of Dewar resonance structures is a measure of the triplet contribution to its ground state. We present a 2-dimensional organized study of rectangular benzenoids having both armchair and zigzag edges that play an important role in the electronic properties of nanographene patches and strips. Analytical expressions for the number of Dewar resonance structures (DS) for select series of rectangular benzenoid hydrocarbons are presented for the first time. An index of biradical character present (BRC) in polycyclic aromatic hydrocarbons is defined and illustrated. Biradical character is strongly influenced by zigzag edges and the presence of a diradical excised internal structure in polycyclic aromatic hydrocarbons.
authors.affiliation: Department of Chemistry, University of Missouri-Kansas City, Kansas City, Missouri 64110-2499, USA. diasj@umkc.edu
authors.forename: Jerry Ray
authors.initials: JR
authors.lastname: Dias