Aromaticity Polansky index

A few electron density based aromaticity indices have also been proposed. Generalized Polansky index has been defined as... 

Benzene is the prototypical aromatic molecule with 6 n electrons, perfect Z)6h symmetry, aromatic stabilization energy of about 36 kcal/mol, a NICS value of roughly -9 ppm and an appreciable amount of diamagnetic ring current. Aromaticity of an arbitrary molecule is some times judged through its resemblance with benzene via parameters like Polansky index, molecular similarity, Clar s sextet etc. 

In addition to the above, there are other parameters which were put forward to gauge the extent of aromaticity. These include atoms in molecules theory, generalized Polansky index, orbital effect, and polarizability. While each of these parameters measure one of the properties of the molecules in a quantitative fashion, they can be correlated to aromaticity only in conjunction with some other properties. 

Generalized Polansky index [97] gauges the aromaticity of individual benzenoid rings in polyaromatic hydrocarbons [98] by its similarity to benzene. It uses the electron density itself as a tool to explain aromaticity rather than the structural features or quantities derived from electron density. It is derived from the concept proposed by Derflinger and Polansky [99] published in 1967 for explaining aromaticity in polyaromatic compounds and is expressed as follows ... 

Bultinck, R, Ponec, R., Gallegos, A., Fias, S., Damme, S. v., and Carbd-Dorca, R. 2006. Generalized polansky index as an aromaticity measure in polycyclic aromatic hydrocarbons. Croat. Chem. Acta 79 363-371. 

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