I came across this question:

Which is the most stable resonating structure of p-nitrosobenzene among the following?

possible resonance structures of p-nitrosobenzene

I have been taught about the priorities for resonance structure stability as follows:

  1. Complete octet $\rightarrow$ more stable

  2. Uncharged $\rightarrow$ more stable

  3. Lower formal charge $\rightarrow$ more stable

  4. Less separation between opposite charges $\rightarrow$ more stable

  5. Negative charge near more electronegative atoms and positive charge near less electronegative atoms $\rightarrow$ more stable

So according to the above rules, (b) and (c) are the among the most stable. Bu then applying rule #4 above, (b) should be more stable, because here each positive charge is in vicinity of negative charge.

However the answer given is (c). Why is this?

  • 7
    $\begingroup$ A -ve charge on oxygen is better than a -ve charge on carbon, so (c). $\endgroup$ – Sawarnik Apr 7 '17 at 6:41
  • 2
    $\begingroup$ @user43496 For future reference, please consider the dimension and orientation of the figures included. To render the figure more legible, I rotated and down-scaled your photo. $\endgroup$ – Buttonwood Apr 7 '17 at 13:46
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    $\begingroup$ There is no such thing as a most stable resonance structure. $\endgroup$ – Martin - マーチン Jul 1 '17 at 9:53
  • $\begingroup$ Fyi: None of these is a structure for $p$-nitrosobenzene. Properly the name is $p$-nitroso_nitro_benzene. $\endgroup$ – Oscar Lanzi Jul 1 '17 at 23:18

Because on C; the negative charge should be on oxygen (the more electronegative element) instead of on carbon


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