Question

Assertion: trans-butene on reaction with bromine forms racemic mixture.
Reason: trans-compound in trans addition forms two types of stereoisomers.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (D)

With trans-but-2-ene, the product of $Br_2$ addition is optically inactive due to the formation of symmetric meso compounds.



In general, for symmetrical alkenes and symmetrical reagents, the addition takes place as :

cis-alkene + syn-addition $\rightarrow$ meso

trans-alkene + syn-addition $\rightarrow$ racemic

cis-alkene + anti-addition $\rightarrow$ racemic

trans-alkene + anti-addition $\rightarrow$ meso