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JEE Main levelSingle correct optionDifficulty 2 of 3o2025

(E)-But-2-ene reacts with in . The product is

  1. Aa mixture of all three stereoisomers of 2,3-dibromobutane
  2. Bmeso-2,3-dibromobutane
  3. Ca racemic mixture of (2R,3R)- and (2S,3S)-2,3-dibromobutane
  4. D2,2-dibromobutane

Answer: B

Br atoms add anti through a bromonium ion. Anti addition to a trans (E) alkene gives the meso compound (2R,3S), while anti addition to the (Z) alkene gives the racemic (2R,3R)/(2S,3S) pair.
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