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Mechanism of Phenylurethane. 1-butanol and phenyl isocyanate. Mass Spectrometry Interpretation of Mass Spectra. Check Mass Spectrometry Chapters in Lab and Lecture Texts. Molecules of a sample are bombarded by a stream of high energy electrons Molecular ion peak M +.

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slide1

Mechanism of Phenylurethane

1-butanol and phenyl isocyanate

mass spectrometry interpretation of mass spectra
Mass SpectrometryInterpretation of Mass Spectra

Check Mass Spectrometry Chapters in

Lab and Lecture Texts

  • Molecules of a sample are bombarded by a stream of high energy electrons
  • Molecular ion peak M+.
  • Molecular ion bonds break to give fragment IONS and NEUTRAL radicals or molecules. Mass Spectra only show ions, not neutrals.
  • m/z of M+ - m/z of F+ (fragment ion) = mass of neutral
  • Each peak can be interpreted in terms of both a fragment ion and/or a neutral loss
mass spectrometry
Mass Spectrometry
  • Molecular ion peak (M+.) at m/z 32
  • Base peak at m/z 31
  • Fragment ions at 29 and 15

A Mass Spectrum tells you the molecular mass

favored fragmentations
Favored Fragmentations
  • The greater the stability of the fragment ion, the more intense the peak
  • Alkyl ion stability follows carbocation chemistry rules:

3° and allyl more stable than 2°

2° more stable than 1°

  • Acyl ions are stable (m/z 43, 57..)
    • PhC=O+ (m/z 105…)
  • Alpha (a) cleavage in alcohols, amines, ethers
  • Aromatic rings do NOT fragment easily
characteristic fragment ions
Characteristic Fragment Ions
  • Look for alkyl ions at m/z 43, 57, 71, 85 (14 amu or CH2 series)
characteristic fragment ions11
Characteristic Fragment Ions
  • Look for aryl ions at 77 (phenyl), 91 (benzyl), and 105 (benzoyl)
characteristic fragment ions13
Characteristic Fragment Ions
  • Acyl ions are stable (m/z 43, 57..)
acyl fragment
Acyl Fragment

acetophenone

characteristic neutral losses
Characteristic Neutral Losses
  • 15 can only be methyl
  • 17 usually OH
  • 18 always H2O
  • 28 CO or CH2=CH2
  • 29 CH3CH2 or CHO
  • 31 CH3O
  • 35/37 Cl (special isotope pattern too!)
  • 42 CH2=C=O
  • 43 CH3CO or C3H7
  • 45 CH3CH2O or COOH
  • 79/81 Br (special isotope pattern too!)
mass spectrometry summary
Mass SpectrometrySummary
  • Molecular weight:
  • odd-numbered (N ...) ?
  • isotope peaks (Cl, Br)?
  • Alcohols …
  • Recognize typical fragments:
  • H2O, alkyl, acyl, tropylium ion …
slide18

Next time:

  • Bring Spectra of your Unknown #3!
  • Brief Review of Mass Spectroscopy
  • Discussion/Review of H-NMR, CMR