# Determination of the most acidic hydrogen in an organic compound

Identify the most acidic hydrogen in the compound below:

Can someone please explain why is $$\ce{H^\mathrm{a}}$$ in the compound below more acidic than $$\ce{H^\mathrm{b}}$$?

This is what is written in the answer key although the conjugate base obtained from losing $$\ce{H^\mathrm{b}}$$ is stabilized by both resonance, and the inductive electron withdrawing nitro group.

• Anion without Hb is not stabilized by resonance. NO2 is in the wrong position with respect to that OH. – Ivan Neretin Apr 1 at 10:39
• It is stabilized by resonance due to the phenol ring. The stabilizing role of the nitro group is inductive. – user208973 Apr 1 at 10:48
• Well, actually the stabilizing role of NO2 is not just inductive. – Ivan Neretin Apr 1 at 10:58
• Well, another way of looking at it is that the Nitro group is ortho to the ring at the right, and thus decreases electron density in that ring. – William R. Ebenezer Apr 1 at 11:54