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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)(i). trans-But-2-ene with perbenzoic acid, then hydroxide

Question

Complete the following reaction by showing stepwise reaction mechanism for the formation of products: trans-but-2-ene + PhCOOOH, then OH⁻. [structure of the alkene given in the paper]

Answer in brief

Product: meso-butane-2,3-diol, (2R,3S), with benzoate as by-product: syn epoxidation followed by anti (SN2) ring opening, a net anti-dihydroxylation.

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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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Topic notes: addition to alkenes and alkynes (Markovnikov, stereochemistry, dienes), with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversepoxidationPrilezhaev reactionperbenzoic acidanti-dihydroxylationmeso-butane-2,3-diolepoxide opening

All parts of Question 4