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Does steric hinderance stops the benzene ring resonance?

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  • $\begingroup$ Not for phenols to my knowledge $\endgroup$ – Avnish Kabaj Nov 13 '18 at 5:37
  • $\begingroup$ I agree, the 4-nitrophenol will be the more acidic $\endgroup$ – Waylander Nov 13 '18 at 8:18
  • $\begingroup$ But I think due to steric crowding created by two methyl groups, nitro group will go out of the plane and shouldn't take part in resonance. However it decreases the acidity by $-I$ effect , but not by $-R$ effect probably. $\endgroup$ – Soumik Das Nov 13 '18 at 13:11
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The only difference between both compound is the presence of nitro group.

Acidic strength is the ease of giving away H+ and become a stable anion. So let's make the anion in both case.

The phenoxide group, which is present after deprotonation of phenol is highly stable in the first case along with it's +I tendency.

In the second case we have more resonating structure along with already discussed effects of phenoxide we also see that when the nitro group takes of the -ve charge via it's -M effects we see that all atoms have complete octet, making it more stable than first one and because of the higher stability of conjugate base it's acid strength would be more.

So second (nitro, one) is more acidic than the first compound.

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