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JEE Main levelSingle correct optionDifficulty 2 of 3g3090

trans-But-2-ene reacts with singlet dichlorocarbene (from and ). Which statement describes the product correctly?

  1. AAn equimolar mixture of the cis (meso) and trans (racemic) cyclopropanes
  2. B2,3-Dichlorobut-2-ene
  3. Ccis-1,1-Dichloro-2,3-dimethylcyclopropane, a meso compound
  4. Dtrans-1,1-Dichloro-2,3-dimethylcyclopropane, formed as a racemic mixture of two enantiomers

Answer: D

Singlet carbene adds in a single concerted, stereospecific step, so the trans relationship of the methyls is retained. In the trans product, C-2 and C-3 are stereocentres with no internal mirror plane, and attack on either face of the alkene gives the (2R,3R) and (2S,3S) enantiomers in equal amounts. The cis product would be meso, but it does not form from trans-but-2-ene.
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