VKC ScienceChemistry for written exams Telegram

Indian Forest Service (Mains)

Chemistry optional

  • 2 papers
  • 200 marks each
  • 3 h per paper

Paper II covers organic chemistry and spectroscopy.

Indian Forest Service (Mains), Chemistry optional · 2021 · Paper II

Q1(h). Hyperfine lines of an isotopic radical

Question

How many ESR lines are possible for the radical ¹³CF₂H?

Answer in brief

Twelve lines are expected if the two fluorines are equivalent and all distinct splittings are resolved without accidental overlap.

Key points

  • ¹³C has I = ½ and gives a doublet; two equivalent ¹⁹F nuclei, each I = ½, give a 1:2:1 triplet.
  • The proton has I = ½ and splits each component into a doublet.
  • Thus N = (2IC + 1)(2nF IF + 1)(2IH + 1) = 2 × 3 × 2 = 12.
  • Nuclear equivalence, linewidth and accidental coincidence determine how many lines are actually resolved.

The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

Model answer to Q1(h), 2021 Paper II: solution pages 9 and 10
Solution pages 9 and 10 of 40
Read the whole 2021 solution2021 question paper

Topic notes: ESR spectroscopy, the g-value, hyperfine splitting and spin labels, with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversESR spectroscopyhyperfine splittingnumber of ESR lines2nI + 1 rule¹³C and ¹⁹F coupling

All parts of Question 1