MolSynapsequestion bank
MolSynapse / Question bank / Organic Reaction Mechanisms IV: Elimination / E2 mechanism and anti-periplanar requirement
JEE Advanced levelSingle correct optionDifficulty 3 of 3o4200

cis-1-Bromo-2-methylcyclohexane is heated with in ethanol. The major alkene and the reason are:

  1. A3-methylcyclohexene, because the only conformer available has Br and both axial
  2. B3-methylcyclohexene, because the conformer with axial Br has no axial H on C2
  3. C1-methylcyclohexene, because the conformer with axial Br and equatorial has an axial C2-H anti to Br
  4. Dmethylenecyclohexane, because methyl hydrogens are anti to Br

Answer: C

In the cis isomer one substituent is axial and the other equatorial. The conformer with axial Br and equatorial puts the H on C2 axial and trans to Br (anti-periplanar), so removal of it gives the trisubstituted Saytzeff alkene 1-methylcyclohexene. No diaxial Br/ arrangement exists for the cis isomer.
Practice Organic Reaction Mechanisms IV: Elimination More on E2 mechanism and anti-periplanar requirement
Previous questionNext question

More questions on E2 mechanism and anti-periplanar requirement