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My question is how to find the number of aromatic rings in triphenylene:

triphenylene

My professor said that there are 3 aromatic rings, after which he added that the carbons of the middle rings are only supporting ortho-fusion of rings and hence the center ring is not to be considered.

But I am not satisfied. Why not consider the center ring since the electron after all delocalizes in the entire system giving me 4 as the answer? Someone, please clear my confusion out here.

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    $\begingroup$ Clar's rule $\endgroup$ – Mithoron Jul 30 at 14:56
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    $\begingroup$ Basically, you're right and your prof is wrong. The middle ring is not that aromatic (alternating long and short bonds), but it's flat, and certainly the center of one big pi-system, not just holding together three individuals. $\endgroup$ – Karl Jul 30 at 19:04

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