This organic compound is a conjugated 10 pi electron cyclic system and according to Huckel's rule it should display aromaticity.

[citation needed] Yet even isomer (3) is unstable, suffering from steric repulsion between the two internal hydrogen atoms,[6] and tends to distort into the perimeter of two fused circles, one larger and the other smaller, as in azulene.

One method is to formally replace two hydrogen atoms by a methylene bridge (−CH2−); this gives the planar bicyclic 1,6-methano­[10]annulene (5).

Indeed, 1,6-methano­[10]annulene has no bond length alternation in its X-ray structure and signs of a telltale diamagnetic ring current in its NMR spectrum.

[3] Likewise, a tricyclic methine bridge gives an aromatic structure (6) similar to the stable oxonium ion oxatriquinacene.