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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 · 2022 · Paper II

Q4(a)(ii). Loss of optical activity of an imine with sodium ethoxide

Question

The compound A is optically active and upon treating A with alcoholic sodium ethoxide, it loses its optical activity. Justify. [structure of imine A given in the paper]

Answer in brief

Ethoxide removes the α-hydrogen to give a planar, delocalised 2-azaallyl anion; reprotonation gives racemic A and the achiral isomer Ph(CH₃)C=N–CHPh₂, so optical activity is lost.

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Topic notes: reactive intermediates (carbocations, carbanions, radicals, carbenes, nitrenes, benzyne), with every Civil Services, IFoS and Geo-Scientist PYQ →

Topic notes: stereochemistry and conformational analysis (R/S, E/Z, Fischer and Newman projections, cyclohexane chair), with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversracemisation2-azaallyl anionimine1,3-proton shiftcarbanionsodium ethoxide

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