JEE Main · 2023 · 24 Jan 2023 · Shift 2 · Aldehydes Ketones and Carboxylic Acids

Each compound loses the hydrogen sitting between two electron-withdrawing groups, and the ease of loss tracks the stability of the resulting carbanion. In pentane-2,4-dione that hydrogen lies between two ketone carbonyls, so the anion is delocalised over two strong acceptors and the $\mathrm{p}{K}_a$ is close to $9$. The $\beta$-keto ester places the hydrogen between one ketone and one ester, and the malonate diester between two esters; the ester carbonyl withdraws less, so both stabilise the anion less and have higher $\mathrm{p}{K}_a$. The hydrogen flanked by two ketones is given up most readily, so the diketone alone deprotonates most easily.