chapter 17 - spectroscopy

• the m+ peak is the positive ion formed when a molecule loses an electron
• a mass spectrometer detects the mass to charge ratio (m/z)
• other peaks on a mass spectrum are caused by fragment ions
• two types of vibrations in a bond:

  • stretch (side to side)
  • bend (up and down)
• the amount a bond stretches or bends depends on:

  • the mass of the atoms in the bond, heavier atoms bend slower
  • the strength of the bond, the weaker the bond, the faster the vibrations
• using infrared spectroscopy

  1. the sample is placed inside the IR spectrometer
  2. a beam of IR is passed through
  3. the molecule absorbs some of the IR, and the beam is analysed
  4. computer plots the graphs
• any particular bond can only absorb radiation that has the same frequency as the natural frequency of the bond
• the fingerprint region contains unique peaks at the end of the spectrum
• applications of infrared spectroscopy

  • pollutants can be identified to detect emissions
  • breathalysers to see alcohol
• elemental analysis - use of percentage composition data to determine the empirical formula