Theoretical evaluation of electron delocalization in aromatic molecules by means of atoms in molecules (AIM) and electron localization function (ELF) topological approaches

In most textbook definitions, the delocalization of π-electrons is invoked as the driving force of aromaticity. This review describes several criteria of aromaticity that are based on the analysis of electron delocalization. Focus is on the description of those works that analyze electron delocalization and aromaticity employing the most common methods to measure delocalization: the atoms in molecules theory and the electron localization function. It is shown that the theoretical studies of electron delocalization have significantly improved the understanding of aromaticity, providing useful information concerning the analysis of some interesting features of this phenomenon such as the aromaticity in fullerenes, substituent effects, electrophilic substitution, and homoaromaticity.