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I guess I'm just trying to understand what "cyclic resonance" really means, from all the examples I've come across its always a cyclic system where the pi-electrons go all around the molecule and come back to its same position. It fails to do that here because the cycle stops at the C+ and 'comes back to the oxygen'. If this is a valid example for cyclic resonance, whats the difference between this and just a regular conjugated system that's planar but not in a loop.

[edit] does the cyclic resonance talk about all the pi electrons being a part of a 'loopy' system? I mean, can I think of aromaticity as something that contains a fuel-part and a ignite-part; the fuel would be 4n+2 pi electrons in a loopy system and the pi-electron sets are adjacent to each other and the ignite-part which would be the carbocation here?

any help is appreciated.

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    $\begingroup$ Note that what you've drawn is a (very) minor resonance contributor to the pyrylium ion. $\endgroup$ Commented May 16 at 3:03

1 Answer 1


As noted by Nicolau in the comments, this is really the pyrylium ion. It is usually drawn with a double bond to the oxygen atom, which then formally takes the positive charge. This allows an extra pi bond to be drawn elsewhere in the ring:

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As reported by the referenced Wikipedia article, this ion meets the simple rules for aromaticity and experimentally shows evidence of extra stability due to this aromatic character. The ion is stable enough to be made and sold commercially.

Often in natural organic materials the pyrylium ring is further stabilized by conjugating or cumulating it with additional aromatic carbocycles. The intense colors in berries, for example, come from anthocyanins, in which the pyrylium cation ring shares an edge with another aromatic ring and is conjugated with a third aromatic ring.


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