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JEE Main levelSingle correct optionDifficulty 2 of 3hc065

trans-But-2-ene is treated with bromine in . The product is

  1. A1,2-dibromobutane
  2. Bmeso-2,3-dibromobutane
  3. C2,2-dibromobutane
  4. Da racemic mixture of (2R,3R)- and (2S,3S)-2,3-dibromobutane

Answer: B

Bromine adds anti through a bromonium ion. Anti addition to the trans-alkene places the two Br atoms so that the product has a mirror plane, i.e. meso-(2R,3S)-2,3-dibromobutane. Anti addition to the cis-alkene would give the racemic pair.
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