Mass spectra & IR -2

  • Created by: Shannon
  • Created on: 09-05-14 16:02
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  • Mass spectra & IR
    • Mass spectrometry can differentiate between similar molecules
      • Mass spectrometry can tell 2 similar molecules apart, because they won't produce exactly the same set of fragments
      • E.g Propanal and Propanone
        • Have the same Mr but possess different structures, so different fragments are produced
          • Propanal will produce a C2H5 fragment, when propanone won't
    • Mass spectrometry is used to find...
      • Relative isotopic masses
      • The abundance of different isotopes
      • Relatively molecular mass
        • Look at the molecular ion peak
          • The molecular ion can be broken into fragments
            • Fragmentation pattern seen
    • Infrared radiation
      • Some molecules can absorb the energy from IR
        • Makes their covalent bonds vibrate
        • Only molecules made of different atoms can absorb IR
          • Polarities of the bond changes as they vibrate
        • E.g CO2, H2O, NO & CH4
        • Gases that absorb IR are called greenhouses gases
          • Stops some of the radiation emitted by the Earth from escaping
            • Trapped in atmosphere
      • IR spectroscopy helps to identify organic molecules
        • Shows what frequencies of radiation the molecule is absorbing
          • Can identify functional groups
            • C-H stretch in alkanes, alkenes and aldehydes
            • O-H stretch in alcohols and carboxylic acids
            • N-H stretch in amines
            • C=O stretch in aldehydes and ketones
            • C-X stretch in halogenoalkanes


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