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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 · 2022 · Paper II

Q5(d). N–H stretching of amines in IR; alcohols in PMR

Question

(i) How will you distinguish between NH stretching absorption of a primary amine and a secondary amine by using IR spectroscopy? (ii) How will you distinguish among primary, secondary and tertiary alcohols on the basis of PMR spectroscopy?

Answer in brief

(i) Primary amines show two N–H stretches (≈ 3500, 3400 cm⁻¹), secondary amines one weak band (3350–3310 cm⁻¹); (ii) H–C–O protons: 2H, 1H, none; OH in dry DMSO-d₆: triplet, doublet, singlet.

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

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

CoversIR spectroscopy aminesN–H stretchingPMR alcoholsDMSO-d₆D₂O exchangeNMR spin coupling

All parts of Question 5