Question: Explain why H_a is much less acidic than H_b . Then draw a mechanism for the following reaction.

The protons are more acidic when the adjacent group is more electron-withdrawing.The ester is an electron-withdrawing group that stabilizes the carbanion due to the presence of the carbonyl group.

Hence, the ester attracts its electron from the adjacent proton making it more acidic.

The H_a is much less acidic because the delocalization of the carbanion can't occur by the removal of H_a .

Removal of H_a with base does not generate an anion that can delocalize onto the carbonyl O atom, whereas removal of H_b generates an enolate that is delocalized on O.

Abstraction of the acidic proton

Abstraction of the acidic proton

The mechanism of the given reaction is shown as:

Reaction mechanism