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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 I covers physical and inorganic chemistry.

UPSC Civil Services (Mains), Chemistry optional · 2025 · Paper I

Q8(e). Two oxidative additions of methyl iodide

Question

Complete the following chemical reactions and indicate the category of these reactions. Justify your answer. (i) 2[Co(CN)₅]³⁻ + MeI → (ii) [Ru(CO)₃(PPh₃)₂] + MeI →

Answer in brief

(i) 2[Co(CN)₅]³⁻ + CH₃I → [Co(CN)₅(CH₃)]³⁻ + [Co(CN)₅I]³⁻; (ii) [Ru(CO)₃(PPh₃)₂] + CH₃I → [Ru(CH₃)(I)(CO)₂(PPh₃)₂] + CO; both are oxidative additions.

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Topic notes: organometallics: 18-electron rule, oxidative addition, fluxional molecules and Wilkinson's catalyst, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversoxidative additionmethyl iodide18-electron rulepentacyanocobaltateradical mechanismSN2 oxidative addition

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