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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 · 2017 · Mains Paper III

Q9(a). Hexatriene frontier orbitals

Question

State the characteristics of pericyclic reactions. Give the π-MO diagram of 1,3,5-hexatriene and identify ground- and excited-state frontier orbitals.

Answer in brief

Pericyclic reactions are concerted cyclic reorganisations governed by orbital symmetry. Ground-state HOMO/LUMO are ψ₃/ψ₄; photoexcitation promotes an electron from ψ₃ to ψ₄.

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CoversHexatriene frontier orbitalsPericyclic reactions

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