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Indian Forest Service (Mains)

Chemistry optional

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

Paper II covers organic chemistry and spectroscopy.

Indian Forest Service (Mains), Chemistry optional · 2021 · Paper II

Q2(a). Thermal closure of octatriene

Question

Using frontier orbitals and mirror-plane symmetry, predict the thermal disrotatory cyclization of the given (E,E)-2,4,6-octatriene and its product stereochemistry. [structure given in the paper]

Answer in brief

A six-π-electron triene closes thermally by disrotation; the reactive conformation with both terminal double bonds E gives cis-5,6-dimethylcyclohexa-1,3-diene.

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Topic notes: pericyclic reactions, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coverselectrocyclic reactiondisrotatory ring closureoctatrieneWoodward–Hoffmann rulesHOMO symmetry

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