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UPSC Civil Services (Mains)

Chemistry optional

  • 2 papers
  • 250 marks each
  • 3 h per paper
  • 5 of 8 questions, Q1 and Q5 compulsory

Paper II covers organic chemistry and spectroscopy.

UPSC Civil Services (Mains), Chemistry optional · 2023 · Paper II

Q5(d). LiAlH₄ reduction of camphor: OH cis to the bridge

Question

Reduction of camphor with LiAlH₄ leads to 90% of the isomer in which the OH group is cis to the bridge. Give a suitable explanation of this observation.

Answer in brief

Hydride attacks C=O from the less hindered endo face; the syn-7-methyl group of the bridge blocks the exo face. OH ends exo, cis to the bridge (isoborneol, 90 %): steric approach control.

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Topic notes: reagents for oxidation, reduction and hydroboration, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coverscamphor reductionLiAlH₄isoborneolsteric approach controlexo/endo attack

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