JEE Main · 2021 · 25 Jul 2021 · Shift 2 · Hydrocarbons

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For the reaction of (E)-but-2-ene type alkene [H₃C-CH=CH-CH₃, structure shown] with Br₂ in CCl₄ giving product 'P', the total number of stereoisomers possible for product 'P' is ______.

Answer: 2

Solution

The source structure is cis-/(Z)-but-2-ene (both

C H_{3}

groups on the same side). Anti addition of

B r_{2}

CC l_{4}

to the cis alkene gives

(\pm)

-2,3-dibromobutane — a pair of enantiomers — so the total number of stereoisomers of P is 2. (Note: the stem's '(E)' label is incorrect; the source depicts the Z isomer, which is what gives 2 stereoisomers.)

JEE Main · 2021 · 25 Jul 2021 · Shift 2 · Integer answer

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