Aromaticity of Carbon Nanotubes

Carbon nanotubes (CNTs) are aromatic, peri-condensed benzenoids, composed of sp2 carbon atoms; the carbons are arranged in a graphite-like, hexagonal pattern. The aromatic character of armchair and zigzag nanotubes was compared with the corresponding rectangular graphite sheets, from which CNTs may be derived. The number of Kekulé structures in (2,2)m and (4,0)m CNTs and in planar rectangular graphite sheets of equivalent size, where m denotes the number of strips making up the CNTs (1 ≤ m ≤ 5), was determined. The aromatic character of the structures was estimated by using the Swinborne-Sheldrake equation. It was found that (2,2) CNTs are more aromatic than their planar counterparts and (4,0) CNTs. (4,0) CNTs are less aromatic compared to the corresponding planar structures. Hence it is more difficult to saturate (and functionalize) armchair CNTs than the corresponding planar graphite structures and zigzag CNTs.