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JEE Main levelSingle correct optionDifficulty 2 of 3g3089

cis-But-2-ene is treated with and a zinc-copper couple in ether (Simmons-Smith reaction). The product is

  1. A1,1-Dimethylcyclopropane
  2. Bcis-1,2-Dimethylcyclopropane (meso)
  3. CA racemic mixture of trans-1,2-dimethylcyclopropane
  4. DA 1:1 mixture of the cis and trans isomers

Answer: B

The zinc carbenoid transfers to both ends of the double bond in one concerted step, so the geometry of the alkene is retained (stereospecific syn addition). The two methyl groups that were cis stay cis, giving the achiral (meso) cis-1,2-dimethylcyclopropane.
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