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Monterino Overson

Why is cycloheptatrienyl cation aromatic?

Clark Bull-Misner  Follow

Cycloheptatrienyl cation, which is also known as tropylium cation, is aromatic. Because, it maintains the Huckel's rule of aromaticity. After removal of one hydride ion from only saturated carbon of cycloheptatriene, a vacant orbital appears on that C atom. Then 6 π electrons are delocalized throughout the seven membered ring. Thus the tropylium cation becomes planar and it has (4n + 2) π electrons (n = 1) and these π electrons are delocalized throughout the entire ring. Resonance structures of tropylium cation:

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Bertrand Wengher  Follow

It has to be noticed that, by its name ending in -yl (like methyl, ethyl etc), cycloheptatrienyl is no substance, but something derived from cycloheptatriene, which is not aromatic, as, for once, it is not planar.

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