If we take a look at conjugate base of benzoic acid it is as given below:

enter image description here

Now my question is:

Is delocalisation of non bonding electrons(in the carboxylate part) into the benzene ring possible?

Critical Comment:I think that it won't be possible because we would end up having negative charge on both the oxygen which should make it less stable.

Reference supporting my claim:

Although the reason I gave may or may not be the actual,i don't know, but the reference also claims the same thing i.e delocalisation of non bonding electrons doesn't occur.

Link: https://www.asu.edu/courses/chm233/notes/acids/acids2017.html

scroll down and check this: Factors controlling acidity and under that check 'substituent effects for some aromatic carboxylic acids'


Well definitely not. The simplest answer would be that if you tried to do it, you would get a really absurd Resonance structure. What would actually occur is - The non bonding electrons would delocalise only between the oxygen atoms and the benzene ring would have its own separate electron delocalisation(as in a normal benzene ring)which would have nothing to do with the former. This would be favored because-

1.The non bonding electron would be with only oxygen(which is more electronegative and hence gives better stabilizing effect to the resonance hybrid).

  1. It gives rise to equivalent resonance structures which greatly enhance stability
  • $\begingroup$ Is any form of delocalisation possible where the benzene ring participates in resonance with carboxylate ion? If no such thing is possible then ortho effect would make no sense because if no resonance occurs in the first place between the ring and the carboxylate ion then we cant use the concept of steric inhibition of resonance $\endgroup$ – Banchin Jul 12 '18 at 7:09
  • $\begingroup$ I knew this point would come up. Ortho effect is an experimental observation which we try to explain via theoretical Organic Chemistry. Hence there is more than 1 explanation to the problem, of which the conjugate base explanation is a bit weird(as said by my teacher and not justified). There's another one involving resonance in the acid itself which also involves SIR which seems more valid. Check it out if you want to. And my answer is pretty much valid according to the explanation I am referring to. $\endgroup$ – LightningNeo02 Jul 12 '18 at 8:39
  • $\begingroup$ Isn't Steric inhibition of Resonance(SIR) effect similar to that of ortho effect.It's just that if SIR occurs in benzoic acid then it is Ortho effect right?...And moreover you provided no answer to my question about the existence of any other resonance structure involving benzene ring.It would be great if you explain the question in my previous comment as it would clear a lot of doubts for me. $\endgroup$ – Banchin Jul 12 '18 at 8:50
  • $\begingroup$ This is wrong. Of course there is conjugation between the carboxyl group and the aromatic ring, they are after all in plane and belong to the same pi system. Just because you cannot draw a valid Lewis structure for this resonance contributor, it doesn't mean that the contribution does not exist. $\endgroup$ – Martin - マーチン Jul 12 '18 at 8:57
  • $\begingroup$ @Martin-γƒžγƒΌγƒγƒ³ if there is conjugation what is it? Could you please provide the resonance structures $\endgroup$ – Banchin Jul 12 '18 at 9:41

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