A-Level Competing definitions of acids and bases: worked solution

Question

In step 2 of the iodoform mechanism the hydrogens are replaced one after another because OH- repeatedly removes an H+ from the alpha methyl group. State how the methyl ketone is behaving in this step and explain how it is able to release the H+.

In this step the methyl ketone is acting as a Bronsted-Lowry acid (a proton/H+ donor) towards the OH-. It can release the alpha H+ because that C-H bond is acidic: when the H+ leaves, the resulting negative charge on the alpha carbon (carbanion) is stabilised by delocalisation onto the adjacent electronegative carbonyl oxygen, forming a resonance-stabilised enolate ion. This stabilisation makes loss of the alpha H+ favourable.