A Levels Chemistry (9701)•9701/12/M/J/24
Explanation
Elimination Reaction in Alcoholic Base
Steps:
- 1-Bromopropane (CH₃CH₂CH₂Br) undergoes reaction with ethanolic NaOH, favoring elimination over substitution.
- In E2 mechanism, OH⁻ abstracts β-hydrogen, Br leaves, forming a double bond.
- Product is propene (CH₃CH=CH₂) by removing HBr.
- Molecular formula of propene is C₃H₆.
Why A is correct:
- Elimination of HBr from 1-bromopropane yields propene, C₃H₆, per Zaitsev's rule for alkenes.
Why the others are wrong:
- B: C₃H₈ is propane, requiring reduction, not base elimination.
- C: C₃H₆O suggests an unsaturated alcohol, but no oxygen incorporates in elimination.
- D: C₃H₈O is propan-1-ol, from SN2 substitution in aqueous NaOH, not ethanolic.
Final answer: A
Topic: Halogen compounds
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