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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

Q8(b)(ii). Expected J(Ha–Hb) in three alkenes

Question

Estimate the expected splitting (J in Hz) for the lettered protons in the above compounds. [structures (A), (B), (C) with Ha and Hb marked given in the paper]

Answer in brief

(A) geminal, ²J ≈ 0–3 Hz (about 1–2 Hz); (B) geminal, ²J ≈ 0–3 Hz (about 1–2 Hz); (C) cis-vicinal in a six-membered ring, ³J ≈ 10 Hz (8–11 Hz).

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Coverscoupling constantgeminal couplingvicinal couplingKarplus relationalkene protons

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