JEE Main · 2021 · 01 Sep 2021 · Shift 2 · Hydrocarbons

The stereoisomers that are formed by electrophilic addition of bromine to trans-but-2-ene is/are

(A)2 enantiomers and 2 mesomers
(B)2 enantiomers
(C)1 racemic and 2 enantiomers
(D)2 identical mesomers✓ Correct

Answer: (D)

Solution

Bromine adds through a cyclic bromonium ion, which forces anti addition of the two bromine atoms. For trans-but-2-ene anti addition sets the two new stereocentres with opposite configurations, producing a species with an internal mirror plane. Attack on either face of the bromonium ion gives the same achiral molecule, so the two routes give two identical meso forms of 2,3-dibromobutane.

JEE Main · 2021 · 01 Sep 2021 · Shift 2 · Single correct option

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