This paper reports the application of the recently proposed formalism known as generalized population analysis (GPA) as a new means for the quantitative characterization of the aromaticity of various benzenoid rings in polycyclic aromatic hydrocarbons (PAHs). The quantity which we propose as a new measure of aromaticity is the so-called six-center bond index. The values of this index characterize the extent of delocalized cyclic bonding in individual benzenoid rings of PAHs and it is shown that the scale of the aromaticity represented by this index closely reflects the intuitive idea according to which the aromaticity of individual rings in PAHs can be gauged by the degree of similarity to benzene itself. In addition, the relation of the newly introduced index of aromaticity to other existing aromaticity measures is discussed. Consistent with the presumed orthogonality of classical and magnetic criteria of aromaticity, the classifications based on these two classes of aromaticity measures were found usually to be opposite.

Molecular aromaticity in the linear polyacenes is investigated using an atoms in molecules based six center index (SCI-AIM) which measures the electron delocalization. SCI-AIM values for the linear polyacenes indicate decreasing aromaticity going from outer to inner rings in the polyacene series. The SCI-AIM approach is compared to a Mulliken-like approach, and a critical comparison to the PDI index is made.