6-Electron exchange function as a simple estimator of aromaticity in large polyaromatic hydrocarbons

The 6-electron exchange function (6-EEF) is defined and calculated for a series of large polyaromatic hydrocarbons (PAHs). It is shown that the 6-EEF, computed at selected points in space, is able to reproduce in PAHs the same relative values as the multicenter electron delocalization indices with an affordable computational cost and without using any definition of the atom in the molecule. Calculations for a series of D6h PAHs ranging from C6H6 to C216H36 are performed. The results can be extrapolated to even larger PAHs and allow predicting the behaviour of a benzene ring in an infinite sheet of graphite.