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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)(i). Coupling constants of the lettered protons

Question

Estimate the expected splitting (coupling constant J in Hz) for the lettered protons in the ¹H NMR spectrum of the following compounds A, B and C. [structures given in the paper]

Answer in brief

A: ²J ≈ 0–3 Hz, two doublets; B: one singlet, no splitting seen; C: ⁴J ≈ 2.5 Hz, triplet + doublet.

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Coverscoupling constantgeminal couplinglong-range couplingmagnetic equivalence¹H NMR

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