2022 H2 Chem P1 Q19 — Introduction to Organic Solution

The answer is B (isomerisation).

\(\text{CH}_2\text{=CHCH}_2\text{OH}\) and \(\text{CH}_3\text{CH}_2\text{CHO}\) are both \(\text{C}_3\text{H}_6\text{O}\): no atoms are gained or lost, and only the bonding is rearranged. Within the molecule the C=C is reduced and the \(-\text{CH}_2\text{OH}\) is oxidised to \(-\text{CHO}\), so overall there is no oxidation or reduction. Reactant and product are structural isomers, so the reaction is an isomerisation.

• A is wrong: hydrogenation adds \(\text{H}_2\), which would give a product with more hydrogen, such as propan-1-ol, \(\text{C}_3\text{H}_8\text{O}\).
• C is wrong: overall oxidation would remove hydrogen (or add oxygen), for example giving propenal, \(\text{C}_3\text{H}_4\text{O}\); the molecular formula here is unchanged.
• D is wrong: overall reduction would add hydrogen; the molecular formula here is unchanged.