2017 H2 Chem P1 Q24 — Halogenoalkane Solution

The answer is C (1 only).
\(\text{OH}^-\) can act as a nucleophile (substitution, the main reaction) or as a base (elimination, a side reaction).
• Statement 1 is a possible by-product: \(\text{OH}^-\) removes an H from C-2 as HBr is eliminated, giving propene: \(\text{CH}_3\text{CH}_2\text{CH}_2\text{Br} + \text{NaOH} \rightarrow \text{CH}_3\text{CH}{=}\text{CH}_2 + \text{NaBr} + \text{H}_2\text{O}\).
• Statement 2 is not a by-product: 1-bromopropane has only one Br, so substitution can introduce only one OH. The diol would need a second reaction, such as mild oxidation of propene, and no oxidising agent is present.
• Statement 3 is not a by-product: the Br is on C-1, so substitution gives propan-1-ol, not propan-2-ol. Propan-2-ol could only come from hydration of propene, which needs an acid catalyst and does not occur in aqueous NaOH.
• A is wrong: it includes statements 2 and 3, which cannot be formed.
• B is wrong: it includes statement 2, the diol, which cannot be formed.
• D is wrong: it includes statements 2 and 3, which cannot be formed, and leaves out propene (statement 1).