Ortho Meta Para ACIDS

[dane4695]

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Question:

If you have a phenol with a nitro (NO2) group on ortho to the hydroxyl or one that is para to the hydroxyl, which will be more acidic, and why? I don't completely understand this concept (correct answer is NO2 ortho to OH)

 

[ScottW3]

A nitro group is electron withdrawing and thus will stabilize the negative charge on the deprotonated OH group. This will be most effective in the ortho and para positions to the OH through resonance. BUT, keep in mind that since a nitro group also has a positive charge on it (and a positive charge is one of the most electron withdrawing groups) the phenol with a nitro ortho will be most acidic because the positive charge is closer to the negative charge from the deprotonated OH and thus will stabilize it through an inductive effect. Hope this helps.