Mass spectrometry

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Mass spectrometry

• L.O.
• Use molecular ion peaks and fragmentation peaks
  to identify structures

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• http//www.youtube.com/watch?vJ-wao0O0_qM

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• The mass spectrum of magnesium

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EtOH
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• Molecular ion the main peak furthest to the
  right of the mass spectrum.

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butanone CH3CH2COCH3
Mr 72
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methyl butanoate CH3CH2CH2COOCH3
Mr 102
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bromomethane CH3Br
79Br81Br 11
CH381Br.
CH379Br.
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chloroethane CH3CH2Cl
35Cl37Cl 31
CH3CH235Cl.
CH3CH237Cl.
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THE MASS SPECTRUM - THE MOLECULAR ION
The small peak (M1) at 115 due to the natural
abundance (about 1) of carbon-13. The height of
this peak relative to that for the molecular ion
depends on the number of carbon atoms in the
molecule. The more carbons present, the larger
the M1 peak.
20 40 60 80 100
Abundance
114
.
m/z
0
10 20 30 40 50 60 70
80 90 100 110 120 130 140
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Mass spectrum of pentane
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Exercise 1 Identify the peaks in the mass
spectra of EtOH and CH3CH2Cl.
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This is the mass spectrum of EtOH. Identify a)
the molecular ion peak. b) the fragment
responsible for causing the peak at m/z 31.

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• Here is the mass spectrum of CH3CH2Cl.
• Identify the molecular ion peaks for this
  molecule
• Give the ratio of relative abundance you would
  expect these peaks to be found in.
• Identify the fragments responsible for causing
  the pair of peaks at 49 and 51.

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butane or methylpropane.
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