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.
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$\begingroup$ Related: chemistry.stackexchange.com/questions/28342/are-these-aromatic/… $\endgroup$– Klaus-Dieter WarzechaJul 16, 2016 at 6:07
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2 Answers
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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.)
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4$\begingroup$ 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 $\endgroup$– Martin - マーチン ♦Jul 14, 2017 at 5:23
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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.
