MolSynapsequestion bank
MolSynapse / Question bank / Organic Reaction Mechanisms IV: Elimination / Dehydration of alcohols and dehydrohalogenation
JEE Advanced levelSingle correct optionDifficulty 3 of 3o4104

cis- and trans-1-Bromo-2-methylcyclohexane are treated with /ethanol (E2, requiring an axial bromine and an anti axial beta hydrogen). Which is correct?

  1. Aboth isomers give only 3-methylcyclohexene
  2. Bthe trans isomer gives only 3-methylcyclohexene, while the cis isomer gives mainly 1-methylcyclohexene
  3. Cboth isomers give only 1-methylcyclohexene
  4. Dthe trans isomer gives mainly 1-methylcyclohexene, while the cis isomer gives only 3-methylcyclohexene

Answer: B

In the reactive trans-diaxial chair of the trans isomer, Br and the C-2 methyl are both axial, so C-2 has no axial hydrogen; the only anti hydrogen is at C-6, giving 3-methylcyclohexene. In the cis isomer the chair with axial Br has the methyl equatorial, so the C-2 hydrogen is axial and anti, and Saytzeff elimination to 1-methylcyclohexene is possible.
Practice Organic Reaction Mechanisms IV: Elimination More on Dehydration of alcohols and dehydrohalogenation
Previous questionNext question

More questions on Dehydration of alcohols and dehydrohalogenation