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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 · 2016 · Mains Paper III

Q11(b). Ylides and Wittig selectivity

Question

Define ylides. Explain how stabilised and unstabilised phosphorus ylides differ in Wittig reactions with cyclic ketones.

Answer in brief

A phosphorus ylide has adjacent formally opposite charges, Ph₃P⁺-C⁻R₂; stabilisation changes reactivity and often alkene stereoselectivity.

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CoversYlidesWittig selectivityAlkene synthesis

All parts of Question 11