Patterns of pi-electron delocalization in aromatic and antiaromatic organic compounds in the light of Huckel's 4n+2 rule

The total pi-electron delocalization of a series of classical aromatic and antiaromatic organic compounds is separated into ortho ( 1,2), meta ( 1,3), para (1,4), and successive contributions (the so-called delocalization crossed terms) and the changes that take place in these crossed terms when two electrons are added or removed are analyzed. Our results show that these changes follow a similar alternation pattern in all cases. The patterns found represent a kind of electronic footprints that makes it possible to discern between aromatic and antiaromatic systems.