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JEE Main202331 Jan 2023Morning ShiftChemistryHydrocarbonsActual

Choose the correct set of reagents for the following conversion trans Ph - CH = CH - CH 3 → cis Ph - CH = CH - CH 3

Options

  1. ABr 2 ,  alc  KOH , NaNH 2 , Na LiqNH 3
  2. BBr 2 , alc  KOH , NaNH 2 , H 2 Lindlar Catalyst
  3. CBr 2 , aqKOH , NaNH 2 , H 2 Lindlar Catalyst
  4. DBr 2 , aq KOH , NaNH 2 , Na LiqNH 3

Correct answer

B. Br 2 , alc  KOH , NaNH 2 , H 2 Lindlar Catalyst

Step-by-step solution

A trans alkene can be converted to a vicinal dihalide through a halogenation reaction. The vicinal dihalide can undergo double elimination to afford an alkyne. The alkyne can undergo partial reduction to give a cis alkene. The reagents needed to convert trans ( Ph   -   CH   =   CH   -   CH 3 ) to cis- ( Ph   -   CH   =   CH   -   CH 3 ) are shown in the reaction scheme below.

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