Question:


Consider the above chemical reaction. The total number of stereoisomers possible for Product 'P' is ____________.

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Bromine adds anti across the double bond of cis-2-butene giving 2,3-dibromobutane; count the stereoisomers formed.
Updated On: Nov 4, 2026
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Correct Answer: 2

Solution and Explanation

The alkene in the figure has both CH3 groups on the same side, i.e. it is cis-but-2-ene. Br2 in CCl4 adds in an anti fashion through a cyclic bromonium ion to give 2,3-dibromobutane (CH3-CHBr-CHBr-CH3).
Anti addition to the cis alkene gives the (2R,3R) and (2S,3S) forms in equal amounts (a racemic mixture), not the meso form (the meso form comes from the trans alkene).
Number of stereoisomers in product P = 2.
Answer: 2
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