Aromaticity para-delocalization index

An interesting comparison between several aromaticity indices (harmonic oscillator model, nucleus-independent chemical shift, para-delocalization index, aromatic fluctuation index, multicenter indices, atoms-in-molecules theoretical indices and graph-theoretical indices) concluded that the most reliable ones are based on electron delocalization (08JCC1543). 

Moreover, the mean of all DI of poro-related carbons in a given six-membered ring, called Para-Delocalization Index (PDI), has been defined as an aromaticity criterion based on electron delocalization. This index is closely related to NICS and HOMA indices the higher the PDI indices the higher the absolute value of NICS and the higher the HOMA values, thus reflecting greater aromaticity. 

Second, the substituent effect on the stabiHty and the aromaticity of substituted aza analogs of naphthalene should be considered. Different mono- and disubstituted derivatives of aza- and diazanaphthalenes (with F, Cl, OH, OCH3, and CN substituents) have been studied theoretically (2010JPOC(23)440, 2011CTC(963)263). Electronic (para-delocalization index (PDl), ATI, and FLU), magnetic (NICS), and structural (HOMA) aromaticity indices have been used to describe the local Tt-electron delocalization. It has been pointed out that the decrease of the aromaticity of dia-zanaphthalene can be compensated by the introduction of an... 

Guell, M. Matito, E. Luis, J.M. Poater, J. Sola, M. Analysis of electron delocalization in aromatic systems Individual molecular orbital contributions to para-delocalization indexes (PDl). J. Phys. Ghent. A, 2006,110,11569. 

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