Descriptors of Aromaticity: Electronic Criteria

Cyclic delocalization of mobile electrons in two or three dimensions is probably one of the key aspects that characterize aromatic compounds. Although electron delocalization measures dates back to the 1970s, only until recently these measures have been used to quantify aromaticity. In this chapter, we discuss the different existent descriptors of aromaticity that are based on electron delocalization properties. Before, we briefly introduce the most commonly employed methods to quantify electron delocalization.