# Aromaticity of heterocyclic compound [closed]

This is a question of JAM 2017. According to the answer key the answer is 4. But I found only the last 3 as aromatic . So which one is the 4th aromatic compound? Please explain

• Are you sure about the boron compound? – Waylander Sep 3 '18 at 9:39
• No Sir..I was wrong... It's non aromatic.. I got the correct answer . 1,2,4 and 5. @waylander – user67074 Sep 3 '18 at 9:40

So JAM 2017 is apparently rendering both of the first two compounds as aromatic. This, however, is dubious. The first compound in the list is a pyrone, which not everyone would call aromatic. To make an aromatic contributing structure in pyrone we would have to render the carbonyl group as its zwitterionic structure ($\ce{C^+-O^-}$) and then distribute the positive charge around the ring which has an electronegative oxygen atom. We'd have to weigh the favorable effect of aromaticity against the unfavorable effect of putting a positive charge into an electronegative ring.
As for the second compound, we would need to "polarize" two carbonyl groups and concentrate two positive charges into the small ring, and that is not happening even with aromaticity. There is a saving grace, however: if the $\ce{N-H}$ protons are tautomerized onto the oxygen atoms, converting the "keto" structure to its "enol" form, then the tautomerized molecule is 2,4-dihydroxy-1,3-diazine, which would be unambiguously aromatic.