Double Aromaticity in Monocyclic Carbon Clusters

Abstract

Monocyclic carbon clusters have two kinds of pi molecular orbitals, out-of-plane and in-plane pi molecular orbitals. By using B3LYP density functional method with 6-31G(d) basis set we optimized monocyclic carbon clusters and studied the numbers of out-of-plane and in-plane pi electrons. It was found from electron-count and geometry index that the carbon rings of size 4m+2 are out-of-plane aromatic and in-plane aromatic (doubly aromatic), those of of size 4m are out-of-plane anti-aromatic and in-plane anti-aromatic (doubly anti-aromatic), and those of size 4m+1 and 4m+3 are out-of-plane aromatic and in-plane anti-aromatic. This result was confirmed also from their NICS values.