# Is a pyrylium ring aromatic?

I am trying to figure out which rings in callistephin are aromatic:

I know that the benzene rings definitely are aromatic, but I'm not sure about the ring with the positively charged oxygen (highlighted in red).

How does the Hückel $4n+2$ rule apply to this ring?

• If you take both the rings together, you get a hetero-naphthalene which is aromatic. Other than that you should have asked your former question in a more general way that would have allowed answering both in the same way. – Jan Oct 8 '15 at 20:31
• @Jan can I ask how many pi-electrons are in this hetero-napthalene? – justbehappy Oct 8 '15 at 20:47
• 10, just like in normal naphthalene. (Substitute the $\ce{O+}$ with $\ce{CH}$ and you get naphthalene; that was what I was playing at.) – Jan Oct 8 '15 at 20:49

Pyrylium is aromatic. Following Hückel's rule, pyrylium is uninterrupted (no $$\mathrm{sp^3}$$ hybridization), all atoms have p-orbitals and there is 6 π electrons. the 6 π electrons indicate that Hückel's rule $$(4n+2)$$ is agreeable for pyrylium, $$n = 1$$.