JEE MainChemistryHydrocarbons
Hex- 3 -yne is subjected to reduction using sodium in liquid ammonia to yield product X . In a separate reaction, hex- 3 -yne is reduced using hydrogen gas in the presence of Lindlar's catalyst to yield product Y . Both X and Y are then independently treated with Br ₂ in CCl ₄ . Identify the stereochemical nature of the final dibrominated products obtained from X and Y respectively.
Options
- AX yields a racemic mixture, Y yields a meso compound
- BX yields a meso compound, Y yields a racemic mixture
- CBoth X and Y yield meso compounds
- DBoth X and Y yield racemic mixtures
Correct answer
B. X yields a meso compound, Y yields a racemic mixture
Step-by-step solution
Reduction of hex- 3 -yne with Na in liquid NH ₃ (Birch reduction) yields trans-hex- 3 -ene ( X ). Reduction of hex- 3 -yne with H ₂ in the presence of Lindlar's catalyst yields cis-hex- 3 -ene ( Y ). The addition of Br ₂ in CCl ₄ to an alkene proceeds via an anti-addition mechanism. Anti-addition of bromine to a trans-alkene (like trans-hex- 3 -ene) results in a meso compound. Anti-addition of bromine to a cis-alkene (like cis-hex- 3 -ene) results in a racemic mixture of enantiomers. Therefore, X yields a meso comp