Annulenes Mobius topology

The antiaromatic geometry found along the concerted path of ground-state-forbidden pericyclic reactions, which is topologically equivalent to an antiaromatic Hiickel [4n]annulene or MObius [An + 2]annulene, is a particularly interesting type of biradicaloid geometry. (Cf. Section 4.4.) Other biradicaloid geometries and combinations of those mentioned are equally possible. 

For further discussion of homoaromatic systems, see (a) McEwen, A. B., Schleyer, P. v. R. (1986). In-plane aromaticity and trishomoaromaticity a computational evaluation. Journal of Organic Chemistry, 51,4357-4368. (b) Allan, C. S. M., Rzepa, H. S. (2008). Chiral Aromaticities. A Topological Exploration of Mobius Homoaromaticity. Journal of Chemical Theory and Computation, 4, 1841-1848. (c) Allan, C. S. M., Rzepa, H. S. (2008). Chiral Aromaticities. AIM and ELF Critical Point and NICS Magnetic Analyses of Mobius-Type Aromaticity and Homoaromaticity in Lemniscular Annulenes and Hexaphyrins. Journal of Organic Chemistry, 73, 6615-6622. 

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