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UPSC Combined Geo-Scientist

Chemist

  • 3 descriptive papers
  • 200 marks each
  • 3 h per paper

Mains Paper III covers analytical and organic chemistry.

UPSC Combined Geo-Scientist, Mains · 2024 · Mains Paper III

Q7(a)(ii). Robinson annulation of 2-methylcyclohexane-1,3-dione

Question

Complete the following reactions and sketch a suitable mechanism for these reactions: 2-methylcyclohexane-1,3-dione + ethyl vinyl ketone, CH₃ONa–CH₃OH → ? [structures given in the paper]

Answer in brief

Robinson annulation builds a new cyclohexenone ring: 5,8a-dimethyl-3,4,8,8a-tetrahydronaphthalene-1,6(2H,7H)-dione, C₁₂H₁₆O₂ (racemic), + H₂O, through the Michael adduct (a triketone).

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Topic notes: carbonyl additions and condensations, with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversRobinson annulationMichael additionintramolecular aldol condensationWieland–Miescher ketoneenolate

All parts of Question 7