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JEE Main levelSingle correct optionDifficulty 2 of 3o3134

Each of the two isomers trans-2-chlorocyclohexan-1-ol and cis-2-chlorocyclohexan-1-ol is treated with aqueous NaOH. Which statement is correct?

  1. ANeither gives an epoxide, because a three-membered ring is too strained to form by SN2
  2. BThe cis isomer gives the epoxide faster, because the OH and Cl groups are on the same face
  3. CBoth give the epoxide at the same rate, because both contain OH and Cl on adjacent carbons
  4. DThe trans isomer gives cyclohexene oxide readily, because its alkoxide can attack the C-Cl carbon from the back in the diaxial chair; the cis isomer cannot do so

Answer: D

Epoxide formation is an intramolecular SN2: the alkoxide oxygen must approach the carbon opposite to the C-Cl bond, which requires the O and Cl to be anti (diaxial). In the trans isomer the ring can flip to the diaxial chair and this is possible. In the cis isomer one group is always axial and the other equatorial, so no anti arrangement is available.
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