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MHT CET202526 Apr 2025Morning ShiftChemistryHydrocarbonsActual

Which of the following reagents is used to convert C C triple bond to C = C double bond to give Cis isomer of alkene?

Options

  1. AZnCl ₂ / HCl
  2. BPd-C/quinoline
  3. CNa / liquid NH ₃
  4. DNa / Hg in H ₂ O

Correct answer

B. Pd-C/quinoline

Step-by-step solution

The selective conversion of a carbon-carbon triple bond ( C C ) to a cis alkene requires partial hydrogenation via syn addition. Lindlar's catalyst (Pd-C/quinoline) is specifically designed for this transformation, as the poisoned palladium surface prevents over-reduction while promoting syn addition to yield the cis isomer. Alternative reagents are unsuitable: ZnC l₂ /HCl distinguishes alcohols; Na/liquid NH₃ produces trans alkenes through anti addition; Na/Hg in H₂ O reduces carbonyls rather than alkynes selectiv

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