From bowls to saddles

Abstract

Circulenes can be thought of as dynamic fragments of carbon allotropes, and research into their structures and dynamics can give an insight into the structured and bonding of molecules such as fullerenes. The polynuclear aromatic hydrocarbon- or PAH-like circulenes serve as faithful templates, exhibiting unique molecular dynamics as well as interesting electronic properties. Dynamically, circulenes exhibit their motions in various modes, from bowl inversion to saddle pseudorotation. These motions derive from a balance of aromatic stability and non-planar strain, yielding conformations distinguished by relatively low-energy barriers. All electronic configurations aim to maximize the aromatic character of the molecule. Indeed, all of these molecules are highly aromatic, and their electrons are distributed in resonance forms that maximize the number of 4n+2 Huckel subcircuits. These dynamic and electronic features continue to inspire investigations into novel ideas about molecular dynamics and aromaticity.