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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 · 2025 · Mains Paper III

Q6(a). Singlet and triplet carbenes; fluorenylidene with cis-but-2-ene

Question

Carbenes exist in singlet and triplet states. Which of the two states of carbenes is non-stereospecific in its reaction with alkenes? Explain why. Predict the product/s formed in the following reaction: [9-diazofluorene, hν, cis-2-butene → ?; scheme given in the paper]

Answer in brief

The triplet carbene is non-stereospecific. Product: a mixture of cis- and trans-2,3-dimethylspiro[cyclopropane-1,9′-fluorene].

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

Coverssinglet carbenetriplet carbenefluorenylidenecyclopropanationstereospecific addition9-diazofluorene

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