A Levels Chemistry (9701)•9701/11/M/J/20

Explanation
E2 elimination from tertiary halide forms alkenes
Steps:
- Identify 2-bromo-2-methylpentane as a tertiary halide: CH₃-C(Br)(CH₃)-CH₂-CH₂-CH₃.
- Hot concentrated ethanolic NaOH promotes E2 elimination, removing Br and a β-hydrogen.
- β-Hydrogens available on the two methyl groups (leading to 2-methylpent-1-ene) and on C3 methylene (leading to 2-methylpent-2-ene).
- Both alkenes form; 2-methylpent-2-ene is major due to Zaitsev's rule favoring more substituted alkene.
Why B is correct:
- Matches products from β-elimination: terminal alkene from methyl β-H and internal alkene from chain β-H, per Zaitsev's rule.
Why the others are wrong:
- A: Ignores internal alkene from C3 β-hydrogen.
- C: Misses terminal alkene from methyl β-hydrogen.
- D: 4-methylpent-2-ene requires incorrect branching not present in reactant.
Final answer: B
Topic: Halogen compounds
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