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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 · 2016 · Paper II

Q5(h). McLafferty rearrangement: butyrophenone, m/z 120 and 105

Question

What is McLafferty rearrangement in Mass Spectrometry ? Mass spectrum of 1-phenyl butanone exhibits m/z (mass by charge) 105 as a base peak and m/z 120 as one of the major peaks. Explain.

Answer in brief

m/z 120 = M − C₂H₄ McLafferty (enol radical cation); m/z 105 = M − C₃H₇ α-cleavage (C₆H₅CO⁺, base peak).

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Topic notes: mass spectrometry: molecular ion, metastable peak and McLafferty rearrangement, with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversMcLafferty rearrangementγ-hydrogensix-membered cyclic transition stateα–β bond breaksenol radical cation

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