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Interpreting NMR Spectra

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Interpreting NMR Spectra. Calculate elements of unsaturation (1/2(2C 2-H), ignore ... Count number of signals (equals number of types of H) ... – PowerPoint PPT presentation

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Title: Interpreting NMR Spectra


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  • Interpreting NMR Spectra
  • Calculate elements of unsaturation (1/2(2C2-H),
    ignore O,
  • halogens count as Hs
  • Count number of signals (equals number of types
    of H)
  • Check integration to determine ratio of types of
    H
  • Check splitting to determine connectivity
  • Use chemical shift table to identify types of H
  • Work out fragments
  • Assemble fragments, remembering rules of bonding
  • Check result to make sure it matches formula and
    number
  • of types of H.

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C3H8 EoU0
Signal b, 12 units Triplet, 0.91 ppm
2 signals, 2 types of H
Ratio is 13 or 26
a is a septet, so 6 Hs adjacent b is a triplet,
so 2 Hs adjacent
a is at 1.3 ppm CH2? b is at 0.9 ppm CH3?
Structure is CH3CH2CH3
Signal a, 4 Units Septet, 1.34 ppm
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C4H8O2, EoU1
3 signals, 3 types of H
Ratio is 466 (or 233)
a is a quartet, adjacent to 3H b is a singlet,
adjacent to 0H c is a triplet, adjacent to 2H
a at 4.1 ppm, CH2O? b at 2.0 ppm, CH3CO? c at
1.4 ppm, CH3?
Structure is CH3C(O)OCH2CH3
a, quartet 4 units
b, singlet 6 units
c, triplet 6 units
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Mass Spectrometry
Three things happen to molecules inside a mass
spectrometer 1. The molecules are energized in
some way to create ions. 2. The ions are
separated based on their mass/charge ratio. 3.
The ions are detected.
lt 10-6 mm Hg
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Electron Impact Ionizaton
  • Generate electrons heated filament
  • Accelerate electrons through a potential
    difference (voltage). Commonly electron kinetic
    energy is 80 eV. (conversion 1 eV 96.5 kJ/mole)
  • Enough energy to ionize and cause extensive
    fragmentation.

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Magnetic Sector Mass Spectrometer
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Important Isotopes
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Isotopes in MS
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Branched Hydrocarbons
  • The MS for branched saturated hydrocarbons are
    similar, except certain fragments become more
    prominent.

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IR Spectrometer
  • Lightsource, sample, wavelength selector,
    detector
  • CW and FT

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