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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 · 2021 · Paper II

Q3(c)(i). meso-2,3-Dibromobutane with iodide and with ethoxide

Question

Complete the following reactions along with mechanisms: meso-2,3-dibromobutane with I⁻ gives A, and with EtO⁻ gives B.

Answer in brief

A = (E)-but-2-ene by anti elimination of Br₂; B = (E)-2-bromobut-2-ene by anti elimination of HBr (E2).

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The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

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Read the whole 2021 solution2021 question paper

Topic notes: elimination reactions (E1, E2, E1cB, Saytzeff and Hofmann, anti-periplanar, Chugaev, Cope), 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 →

Coversanti eliminationdebromination with iodideE2 stereospecificitymeso-2,3-dibromobutanetrans-but-2-ene

All parts of Question 3