2023 H2 Chem P1 Q22 — Halogenoalkane Solution

The answer is B (the C-Cl bond is strongest in chlorobenzene).
In chlorobenzene, a p orbital on Cl containing a lone pair overlaps with the delocalised \(\pi\) electron cloud of the benzene ring. The lone pair is delocalised into the ring, so the C-Cl bond gains partial double bond character and is stronger than the C-Cl bond in 1-chloropropane or propanoyl chloride. This is why chlorobenzene does not hydrolyse under normal conditions.
A: Incorrect. Propanoyl chloride, an acyl chloride, reacts more readily with water than 1-chloropropane, a chloroalkane.
C: Incorrect. The leaving group in all three hydrolyses is the same, \(\text{Cl}^-\), so its stability is the same.
D: Incorrect. The carbon bonded to chlorine in propanoyl chloride is electron-deficient, so it is most susceptible to nucleophilic attack, not electrophilic attack.