6
$\begingroup$

I was studying about the resonance and here's my doubt:

enter image description here

How many resonating structures are there in nitrobenzene? Is it 5 (as drawn) or is it 4 because first and the last structures are same or is it 3 because second and fourth structures are also same?

In short, do we count fifth structure when we take the number of resonating structures?

$\endgroup$
4
$\begingroup$

We never really need to know the number of resonance structures. The whole concept is qualitative, so we can't draw any quantitative conclusions from it. But if you want to do it anyway, then of course 1 and 5 are the same, while 2 and 4 are not (they have positive charges on different atoms).

Also, both oxygens are in fact equivalent, so you might want to add the structures with their roles reversed.

$\endgroup$
  • 4
    $\begingroup$ The first and fifth are equal contributors but not the same. $\endgroup$ – jerepierre Sep 28 '16 at 1:18
0
$\begingroup$

If you consider strict symmetry rules, you can only draw 3 really different resonance structures (the first three, from left to right), because all other structures you can draw are symmetrically equivalent to one of those 3 if you rotate it properly, those structures are only useful to show you that there is delocalization of electronic density within those atoms.

$\endgroup$

protected by Community Jul 18 '17 at 17:30

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.