A Levels Chemistry (9701)•9701/12/M/J/22
Explanation
Haloalkane structure determines hydrolysis mechanism
Steps:
- Examine structures: P is tertiary haloalkane (three alkyl groups on carbon with halogen); Q is primary (one alkyl group).
- Recall SN1 mechanism favored for tertiary halides due to stable carbocation formation; SN2 for primary due to backside attack without carbocation.
- Hydrolysis of P proceeds via SN1 as rate depends only on alkyl halide concentration.
- Hydrolysis of Q proceeds via SN2 as rate depends on both alkyl halide and nucleophile concentrations.
Why A is correct:
- P is tertiary, so undergoes SN1 hydrolysis per the rule that 3° halides form stable 3° carbocations, accelerating unimolecular rate-determining step.
Why the others are wrong:
- B: P (tertiary) cannot undergo SN2; steric hindrance blocks backside attack.
- C: Q (primary) favors SN2, not SN1; primary carbocation is unstable.
- D: Q undergoes SN2, but A correctly identifies P's mechanism; question seeks the specified correct row.
Final answer: A
Topic: Halogen compounds
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