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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 · 2019 · Mains Paper III

Q10(d). Frost circles and aromaticity

Question

Use Frost-circle diagrams to explain why cyclooctatetraene is not aromatic but the cyclopropenyl cation is aromatic.

Answer in brief

The three-membered cation has a filled bonding MO with two electrons; planar COT would have a destabilising eight-electron open-shell arrangement and distorts out of plane.

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The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

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Read the whole 2019 solution2019 question paper

CoversFrost circlesaromaticityCyclic molecular orbitals

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