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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3st218

Which statements about the E2 elimination (anti-periplanar H and Br) of cis- and trans-1-bromo-2-methylcyclohexane are correct?

  1. AThe trans isomer reacts faster than the cis isomer because its reactive conformer is the more stable chair
  2. BThe cis isomer can give 1-methylcyclohexene through a chair in which Br is axial and CH is equatorial
  3. CThe trans isomer cannot give 1-methylcyclohexene by anti elimination
  4. DIn the reactive conformer of the trans isomer both Br and CH are equatorial

Answer: B, C

Anti-periplanar elimination needs axial Br and an axial H on the neighbouring carbon. In the cis isomer, axial Br goes with equatorial CH, leaving an axial H on C2, so 1-methylcyclohexene can form. In the trans isomer, axial Br requires axial CH (diaxial), so the C2-H is equatorial and only C6-H is anti, giving 3-methylcyclohexene. That reactive conformer is the less stable diaxial chair, so trans reacts more slowly, not faster.
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