Spectroscopy and Chromatography

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  • Spectroscopy and Chromatography
    • UV and microwave radiation
      • UV has a lot of energy so can cause homolytic fission to form free radicals
        • Cl2 is  split into 2Cl' (very reactive)
          • Destroys the ozone: Cl'+O3-> ClO'+O2       ClO'+O3-> Cl'+2O2
            • The termination step occurs when 2 free radicals combine.
          • Also occurs with methane
      • Microwave ovens heat food by passing through the food molecules and producing an electric field
        • the polar molecules try to align themselves with the field by rotating and collide with each other producing heat.
        • Solids heat up less quickly than liquids as the molecules are less mobile
      • Microwaves are used in the chemical industry to head substances directly, by surgeons to kill cancer cells and to dry wood.
    • Mass spectrometry
      • The sample is bombarded with electrons to create a +ve  ion
      • A mass spectrum is produced, showing the relative amounts of each ion.
        • The peak second from the left is the M peak (molecular mass of the sample)
        • The highest peak is the base peak, caused by a particularly stable ion
    • NMR spectroscopy
      • Protons have spin (causing a tiny magnetic field), which is normally in random directions and so cancel each other out.
        • When an external magnetic field is applied, they align either against (high energy) or with (low energy) the field.
          • They can move between energy levels by emitting or absorbing radio waves.
            • Protons in different environments absorb different frequencies
      • Chemical shift is measured relative to TMS (peak furthest right)
      • Number of peaks = number of hydrogen environments.
      • Area under peaks = ratio of hydrogen enviroments
      • Peaks are split by spin-spin coupling (n+1 rule)
        • This shows the number of protons the hydrogen is adjacent to
      • Used in an MRI machine (safer than X rays)
      • Used to test the purity of samples (each chemical has a 'fingerprint')
    • Infrared spectroscopy
      • IR is absorbed by the bonds in a molecule
        • Each bond will absorb a different wavelength of IR
      • Each peak represents a bond, compare to the data book for identification
      • Used to track  reactions in industry
        • Degree of polymerisation (presence of the double bond)
        • Oxygen in polymers (causes cracking)
    • Chromatography
      • Gas Chromatography
        • Stationary phase: oil mobile phase : nitrogen (HEATED)
        • Detected by heat absorption, and the retention time recorded.
        • Used fto check the purity of a continuous process
      • HPLC
        • Stationary phase: silica + carbon compounds Mobile phase: water+methanol
        • Not heated, so used for chemicals with a high bp, or ones that will decompose on heating
        • Detected by UV
        • Used to check purity of drugs- VERY sensitive.
  • Destroys the ozone: Cl'+O3-> ClO'+O2       ClO'+O3-> Cl'+2O2
    • The termination step occurs when 2 free radicals combine.





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