# Is cycloheptatriene aromatic or not?

Is cyclohepta-1,3,5-triene aromatic?

I think it should not be, because even though the π-system possesses six π-electrons, the conjugation is not complete around the ring.

• Jul 16 '16 at 6:07

You are correct. The conjugation does not extend all the way around the ring, so the molecule is not aromatic. In addition, the single methylene group ($\ce{CH2}$) sticks out of the plane of the rest of the molecule.

(On the other hand, removing a hydride ion $\ce{H-}$ from the $\ce{CH2}$ group leaves the tropylium ion $\ce{C7H7+}$, which is planar and aromatic, with resonance structures putting the positive charge on any of the seven carbons.)

• If the world was black and white, you'd be correct. Unfortunately, aromaticity is among those concepts which have a large grey area: en.wikipedia.org/wiki/Homoaromaticity Jul 14 '17 at 5:23

To define an aromatic compound, there are four basic rules:

• P(lanarity)
• D(elocalization)
• H(ückel's rule): $$4n + 2$$ π-electrons
• C(onjugation)

In the above compound, if any one of the carbon is $$\mathrm{sp^3}$$ hybridised, then it is not planar. In the above compound, there is an $$\mathrm{sp^3}$$ carbon, so it is not aromatic.