Strictly speaking, once we have anything more than a single cycle without conjugated side chains, the Hückel's rule does not really apply, and the very definition of aromaticity becomes somewhat muddy. But that's not an answer they expect from you, anyway. So just point to the first and third rings and call them aromatic, and that would be it.
Why not the second? Well, because the quinone fragment is not aromatic. Its bond length are different from each other. These $\ce{C=O}$ bonds are always double, and the $\ce{C-C}$ bonds next to them are always single; you can't draw a resonance structure where that would be otherwise.
Strictly speaking, once we have anything more than a single cycle without conjugated side chains, the Hückel's rule does not really apply, and the very definition of aromaticity becomes somewhat muddy. But that's not an answer they expect from you, anyway. So just point to the first and third rings and call them aromatic, and that would be it.
Why not the second? Well, because the quinone fragment is not aromatic. Its bond length are different from each other. These $\ce{C=O}$ bonds are always double, and the $\ce{C-C}$ bonds next to them are always single; you can't draw a resonance structure where that would be otherwise.
This is too much of a simplification imho. Either the entire system is aromatic through all of its conjugation, or the conjugation is broken somewhere (cyclooctatetraene). It’s not like the bond lengths of the two phenolic rings be equal whether single or double.More
@Jan, of course my answer contains a good deal of simplification, but I dont agree with your concept either. Surely this whole system is conjugated to some extent, but still we may point out some rings that are "more aromatic" and others that are less so.More
Strictly speaking, once we have anything more than a single cycle without conjugated side chains, the Hückel's rule does not really apply, and the very definition of aromaticity becomes somewhat muddy. But that's not an answer they expect from you, anyway. So just point to the first and third rings and call them aromatic, and that would be it.
Why not the second? Well, because the quinone fragment is not aromatic. Its bond length are different from each other. These $\ce{C=O}$ bonds are always double, and the $\ce{C-C}$ bonds next to them are always single; you can't draw a resonance structure where that would be otherwise.
Strictly speaking, once we have anything more than a single cycle without conjugated side chains, the Hückel's rule does not really apply, and the very definition of aromaticity becomes somewhat muddy. But that's not an answer they expect from you, anyway. So just point to the first and third rings and call them aromatic, and that would be it.
Why not the second? Well, because the quinone fragment is not aromatic. Its bond length are different from each other. These $\ce{C=O}$ bonds are always double, and the $\ce{C-C}$ bonds next to them are always single; you can't draw a resonance structure where that would be otherwise.
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