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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

Q8(c)(i). McLafferty rearrangement; fragmentation of butyl butyrate

Question

What is McLafferty rearrangement? Discuss the mass spectral fragmentation of butyl butyrate with the following given data of ions: m/z 101, m/z 73, m/z 71 and m/z 56. Write the structures of fragment ions.

Answer in brief

McLafferty rearrangement: γ-H transfer to the carbonyl oxygen via a six-membered TS with α,β cleavage and loss of a neutral alkene; butyl butyrate (M⁺• 144): m/z 101 [COOC₄H₉]⁺, 73 [OC₄H₉]⁺, 71 [C₃H₇CO]⁺, 56 [C₄H₈]⁺•.

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CoversMcLafferty rearrangementmass spectrometrybutyl butyrateα-cleavagefragment ionsacylium ion

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