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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

Q5(b). C=C stretch of methylenecyclopropane and methylenecyclobutane

Question

Compare the C=C stretching vibrations in the above compounds (methylenecyclopropane and methylenecyclobutane) and give a suitable explanation for your answer. [structures given in the paper]

Answer in brief

Methylenecyclopropane absorbs at the higher wavenumber: ν(C=C) ≈ 1780 cm⁻¹ against ≈ 1678 cm⁻¹ for methylenecyclobutane.

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Topic notes: IR spectroscopy: group frequencies, carbonyl stretching and hydrogen bonding, with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversIR spectroscopyC=C stretching frequencyring strainexocyclic double bondmethylenecyclopropane

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