2018 H2 Chem P1 Q22 — Carbonyl Compound Solution

The answer is A.
Tollens' reagent is a mild oxidising agent that oxidises an aldehyde group, -CHO, to a carboxylic acid (as the carboxylate ion), and is itself reduced to a silver mirror. It does not oxidise ketones, ethers, alkenes or the OH group in these compounds.
A is \(\text{CH}_3\text{CH}_2\text{CH=CHCH}_2\text{CHO}\) (hex-3-enal). Its terminal -CHO group is an aldehyde, so A is oxidised to \(\text{CH}_3\text{CH}_2\text{CH=CHCH}_2\text{CO}_2^-\) and a silver mirror forms.
• B is wrong: \(\text{CH}_3\text{COCOCH}_3\) contains two ketone groups and no aldehyde group, so it is not oxidised by Tollens' reagent.
• C is wrong: it contains a ketone, an ether in the ring, a methoxy ether group and a C=C bond, but no aldehyde group.
• D is wrong: it contains a ketone, an ether in the ring, a C=C bond and an OH group on the C=C, but no aldehyde group.