A Pedestrian Approach to the Aromaticity of Graphene and Nanographene: Significance of Huckel’s (4n+2)π Electron Rule

Abstract

In an attempt to describe and rationalize the elusive aromatic properties of graphene by first-principles calculations in a simple and transparent way, we have constructed numerous judicially chosen real-space models of various sizes and symmetries, which lead to the aromaticity pattern of infinite graphene by a process of “spatial” evolution through successive peripheral additions, characterized by fundamental periodicities related to the traditional Huckel (4n+2)π electron rule. In accord with the early expectations of Pauling, we have found that the electronic and aromatic properties of infinite graphene result from the superposition of two complementary primary aromatic configurations, in which full and empty rings are interchanged. The primary pattern consists of a hexagonal superlattice in which each fully aromatic ring is surrounded by six nonaromatic rings, in full agreement with the empirical Clar aromatic sextet theory. We have found that, for finite nanographene(s), aromaticity patterns change ...