The Hückel Analysis Plugin is able to calculate different structural descriptors for aromatic atoms. Localization energies L(+) and L(-) for electrophilic and nucleophilic attack at an aromatic center are calculated by the Hückel method. A smaller L(+) or L(-) value means more reactive atomic location. Order of atoms in E(+) or in Nu(-) attack are adjusted according to their localization energies. The total π energy, the π electron density and the total electron density are also calculated by Hückel method. Depending on the chemical environment, the following atoms have optimal Coulomb and resonance integral parameters: B, C, N, O, S, F, Cl, Br, I. All other atoms have a default, non-optimized parameter. Theoretical background is taken from Isaacs' book. Additional literature for the Hückel's parameters is Streitwieser's book.