2018 H2 Chem P1 Q27 — Carboxylic Acid Solution

The answer is B (1 and 4).
• \(\text{H}_2\)/Ni reduces the C=C to C-C but does not reduce the \(\text{CO}_2\text{H}\) group.
• \(\text{LiAlH}_4\) reduces \(\text{CO}_2\text{H}\) to the primary alcohol group \(\text{CH}_2\text{OH}\), but does not reduce the C=C, because \(\text{H}^-\) is a nucleophile and is not attracted to the electron-rich C=C.
• Reaction 1 is correct: \(\text{H}_2\)/Ni saturates the ring and the \(\text{CO}_2\text{H}\) group is kept.
• Reaction 4 is correct: \(\text{LiAlH}_4\) gives \(\text{CH}_2\text{OH}\) and the ring C=C is kept.
• Reaction 2 is wrong: \(\text{LiAlH}_4\) cannot reduce the ring C=C, so the product cannot have a saturated ring.
• Reaction 3 is wrong: \(\text{H}_2\)/Ni does not reduce \(\text{CO}_2\text{H}\), so no CHO group is formed.
So options A (1 and 2), C (2 and 3) and D (3 and 4) are wrong because each includes reaction 2 or 3.