A Hückel Theory Perspective on Möbius Aromaticity

Heilbronner’s Hückel molecular orbital treatment of Möbius 4n−π annulenes is revisited. When uneven twisting in π-systems of small Möbius rings is accounted for, their resonance energies become comparable to iso-π-electronic linear alkenes with the same number of carbon atoms. Larger Möbius rings distribute π-twisting more evenly but exhibit only modest aromatic stabilization. Dissected nucleus independent chemical shifts (NICS), based on the LMO (localized molecular orbital)–NICS(0)_π index confirm the magnetic aromaticity of the Möbius annulenes considered.