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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 · 2024 · Paper II

Q8(b)(ii). Order of J(Ha–Hb)

Question

Arrange the following compounds in order of increasing coupling constant J(Ha–Hb). [structures I, II and III with Ha and Hb marked given in the paper]

Answer in brief

II < III < I, that is geminal (≈ 1.5 Hz) < cis (≈ 11.5 Hz) < trans (≈ 15.5 Hz).

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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 →

Coverscoupling constantKarplus relationgeminal couplingcis and trans coupling¹H NMR

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