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UPSC Civil Services (Mains)

Chemistry optional

  • 2 papers
  • 250 marks each
  • 3 h per paper
  • 5 of 8 questions, Q1 and Q5 compulsory

Paper II covers organic chemistry and spectroscopy.

UPSC Civil Services (Mains), Chemistry optional · 2023 · Paper II

Q3(c). Regioselectivity of Hofmann elimination by Newman projections

Question

Explain the regioselectivity of a Hofmann elimination reaction with the help of Newman projection formula.

Answer in brief

A quaternary ammonium hydroxide gives mainly the less substituted alkene (Hofmann rule): the antiperiplanar conformation needed for the more substituted alkene is crowded by the bulky N⁺Me₃ group.

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Topic notes: elimination reactions (E1, E2, E1cB, Saytzeff and Hofmann, anti-periplanar, Chugaev, Cope), with every Civil Services, IFoS and Geo-Scientist PYQ →

Topic notes: stereochemistry and conformational analysis (R/S, E/Z, Fischer and Newman projections, cyclohexane chair), with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversHofmann eliminationHofmann ruleNewman projectionE2 anti-periplanarquaternary ammonium hydroxide

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