JEE Main · 2024 · Shift-IeasyHC-074

In the given reactions identify A and B.

Hydrocarbons · Class 11 · JEE Main Previous Year Question

Question

In the given reactions identify A and B. image

Options
  1. a

    A:A: 2-Pentyne; B:B: trans-2-butene

    ✓
  2. b

    A:A: n-Pentane; B:B: trans-2-butene

  3. c

    A:A: 2-Pentyne; B:B: cis-2-butene

  4. d

    A:A: n-Pentane; B:B: cis-2-butene

Correct Answera

A:A: 2-Pentyne; B:B: trans-2-butene

Detailed Solution

Step 1: Identify A Pd/C catalyst with \ceH2\ce{H2} (Lindlar-type conditions) gives cis alkene from an alkyne.

Step 2: Identify B Na in Liquid \ceNH3\ce{NH3} = dissolving metal reduction (Birch-type for alkynes). Mechanism: anti addition of H gives trans alkene. image Key Points:

  • Lindlar (\cePd/C\ce{Pd/C} or \cePd/BaSO4/quinoline\ce{Pd/BaSO4/quinoline}): syn addition →\rightarrow cis alkene
  • Na/Liquid \ceNH3\ce{NH3} (dissolving metal): anti addition →\rightarrow trans alkene
  • Always determine internal vs terminal alkyne first

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In the given reactions identify A and B. (JEE Main 2024) | Canvas Classes