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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 · 2025 · Paper II

Q8(a)(ii). Chemical shifts of Hᵃ and Hᵇ

Question

Compare the chemical shifts of the labelled protons Ha and Hb in the ¹H NMR spectrum of the following compounds D and E and justify your answer. [structures of methyl vinyl ether (D) and methyl vinyl ketone (E) given in the paper]

Answer in brief

Hb (enone E) absorbs about 2 ppm downfield of Ha (enol ether D).

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Topic notes: ¹H and ¹³C NMR: chemical shift, spin–spin coupling and coupling constants, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coverschemical shiftshieldingmesomeric effectenol ethermethyl vinyl ketone

All parts of Question 8