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JEE Advanced levelSingle correct optionDifficulty 3 of 3o2037

(Z)-But-2-ene and (E)-but-2-ene are each treated separately with in water. Which statement about the 3-bromobutan-2-ol formed is correct?

  1. AThe (Z)-alkene gives a racemic mixture and the (E)-alkene gives a meso compound
  2. BEach alkene gives a single pure enantiomer
  3. CBoth alkenes give the same racemic mixture
  4. DEach alkene gives a racemic mixture, and the two racemic mixtures are diastereomeric to each other

Answer: D

Anti addition of Br and OH through the bromonium ion is stereospecific. Attack at either carbon of the bromonium ion is equally likely, so each alkene gives a pair of enantiomers (racemate). 3-Bromobutan-2-ol has two stereocentres and no meso form (the groups differ), and the (Z) and (E) alkenes give different diastereomeric pairs.
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