[FIDELIO]

Is this solution missing an additional resonance structure?  I'm thinking about an additional one whereby pi bonds are simply moved around the ring.

Wouldn't we also want to show this additional resonance structure?

Thanks for the help.



 

[spirochete]

You are 100% correct. That is an additional resonance structure. It is equivalent to the other "most important" resonance contributor. So there are really two equally important resonance contributors.

I think this other resonance structure is "less interesting" in some ways because it doesn't show a separate atom carrying the negative charge. But that doesn't negate from the fact that it's a resonance contributor. In a  very rough sense, that resonance structure helps show the aromaticity of the benzene ring.

[hollytara]

I think people sometimes leave off the other aromatic resonance structure because "everybody knows" it exists. 

But of course it is equally important to the one shown.