Leaving group ability determines hydrolysis rate

Steps:

• Hydrolysis of primary 1-bromopropane with water proceeds via SN2 mechanism.
• In SN2, rate depends on leaving group departure, influenced by C-X bond strength.
• Bond dissociation energies decrease down Group 17: C-Cl (351 kJ/mol) > C-Br (285 kJ/mol) > C-I (238 kJ/mol).
• Stronger bonds slow reaction; thus, 1-chloropropane reacts slower than 1-bromopropane.

Why D is correct:

• C-Cl bond strength exceeds C-Br by ~66 kJ/mol, per bond dissociation energy data, making Cl- a poorer leaving group and slowing SN2 hydrolysis.

Why the others are wrong:

• A: 1-Iodopropane hydrolysis is faster due to weaker C-I bond, not lower polarity; polarity decreases down group but bond weakness drives rate.
• B: Water acts as nucleophile, not electrophile; C-I hydrolysis is fast due to good I- leaving group.
• C: Primary alkyl halides favor SN2 (concerted), not SN1 carbocation mechanism.

Final answer: D