Worksheet: Fragment Ions

In this worksheet, we will practice analyzing mass spectra to identify the likely composition of the fragment ions produced from an analyte.

Q1:

What do the presence of M-15, M-29, and M-43 mass spectral peaks correspond to?

  • ALoss of nitrogen atoms
  • BCarbocation rearrangements
  • CAlcohol degradation
  • DSequential loss of alkyl groups

Q2:

Although the molecular ion is usually absent, aliphatic nitro compounds are indicated by which fragment ion peaks?

  • A 𝑚 / 𝑧 = 4 6 and 𝑚 / 𝑧 = 5 8 , corresponding to N O 2 + and C N O 2 +
  • B 𝑚 / 𝑧 = 3 2 and 𝑚 / 𝑧 = 2 8 , corresponding to O 2 and N 2
  • C 𝑚 / 𝑧 = 3 0 and 𝑚 / 𝑧 = 4 6 , corresponding to N O + and N O 2 +

Q3:

What does the fragmentation pattern in a mass spectrum tell us about the sample material?

  • AHow many atoms of each element were present in the original molecule.
  • BWhat kinds of impurities were present and how much of each was there.
  • CWhich functional groups were present in the original molecule.
  • DThe atomic compositions of segments of the molecule that can be reassembled virtually to determine the original structure.

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