Annulene

Annulenes are monocyclic hydrocarbons that contain the maximum number of non-cumulated or conjugated double bonds ('mancude').

With [8]annulene, the molecule takes on a tub shape that allows it to avoid conjugation of double bonds.

[10]Annulene is of the wrong size to achieve a planar structure: in a planar conformation, ring strain due to either steric hindrance of internal hydrogens (when some double bonds are trans) or bond angle distortion (when the double bonds are all cis) is unavoidable.

[5] However, none of the larger annulenes are as stable as benzene, as their reactivity more closely resembles a conjugated polyene than an aromatic hydrocarbon.

In general, charged annulene species of the form [C4n+2+qH4n+2+q]q (n = 0, 1, 2, ...; q = 0, ±1, ±2; 4n + 2 + q ≥ 3) are aromatic, provided a planar conformation can be achieved.