# Why is triptycene aromatic?

I came across this wonderful compound, triptycene.

Why is triptycene an aromatic compound, even though it is non-planar? I thought planarity was a requirement for aromaticity.

• – Tyberius Oct 18 '17 at 16:43
• Each benzene ring is aromatic so the whole molecule is described as aromatic. I doubt the aromaticity extends over the bridging carbons though. – bon Oct 18 '17 at 16:45
• @bon it gets at misconceptions that the OP is having, like that aromaticity is a binary variable and that planarity is an absolute requirement for aromaticity. – Tyberius Oct 18 '17 at 16:54
• For future reference: Aromaticity is not at all an easy concept and there was/is/will be a lot of discussion especially in ambiguous cases. Hückel's rules (plural!) only strictly apply to monocyclic-hydrocarbons, better not overuse it. – Martin - マーチン Oct 19 '17 at 9:57
• Think also of triphenylamine. Is a different example of complexity and variety of chemistry. You will classified as aromatic at first glance (correctly). But there are no inner ring, "just a common substituent" for each ring. However, triphenylamine is also not pyramidal as the N lone pair delocalises indeed! It has a almost planar geometry but whit a tilt of the rings (propeller shape). However you will say it is aromatic independent of this.... – Alchimista Oct 21 '17 at 11:13

Here, if you (incorrectly) try to analyze the whole molecule for aromaticity, you'd get 12 $\pi$ electrons, which is clearly a non-Huckel number, and hence you might infer it as non-aromatic. But however that approach is incorrect. However if I ask you Is biphenyl aromatic? what would you say? The answer is that it's meaningless to ask if biphenyl is aromatic or not. You may however ask Does biphenyl have aromatic ring systems in it?, which is a perfectly valid question.