2024 H2 Chem P1 Q24 — Carbonyl Compound Solution

The answer is B (1 only).
\(\text{LiAlH}_4\) supplies the hydride ion, \(\text{H}^-\), which acts as a nucleophile.
• Statement 1 is correct: O is more electronegative than C, so the C=O bond is polar with a \(\delta+\) carbon. The nucleophile \(\text{H}^-\) attacks this carbon (nucleophilic addition), which is why propanone reacts.
• Statement 2 is incorrect: the C=C bond in propene is electron-rich and non-polar, with no \(\delta+\) carbon. Propene undergoes electrophilic addition, reacting with an electrophile in the first step. This is why it does not react with the nucleophile \(\text{H}^-\).
• Statement 3 is incorrect: \(\text{LiAlH}_4\) reduces the ketone propanone to the secondary alcohol propan-2-ol, \(\text{CH}_3\text{CH(OH)CH}_3\), not to propanoic acid. Forming an acid would be an oxidation.
• A is wrong: it includes statement 2, which is incorrect.
• C is wrong: statements 2 and 3 are both incorrect.
• D is wrong: statement 3 is incorrect, and statement 1, which is correct, is left out.