An Approach to the Aromaticity Based on the Energy of the Occupied π Orbitals

The studies performed during the last ten years on the possibility to determine an aromaticity criterion based on the energy of the occupied πorbitals has been described. The evolution of the research studies to obtain the D criterion defined as {[π1+ Σn2(π1-πn)]0/[π1+ Σn2(π1- πn)]} xa was described. The correlations between D and some other common aromaticity criteria have been presented showing a good relationship between D and other aromatic criteria; D values were used to determine some limits of other aromatic criteria. The role of both DFT functionals and basis sets have been discussed.