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.


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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    $\begingroup$ 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 '17 at 5:23
  • $\begingroup$ But where is the gray area for single hydrocarbon cycles? $\endgroup$ – Oscar Lanzi Jan 9 '18 at 23:26

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