Module 4.2.4- Analytical techniques

• molecular ion


  The positive ion formed in mass spectrometry when a molecule loses an electron.
• Mass spectrometry


  detects the mass-to-charge ratio (m/z) of the molecular ion which gives the molecular mass of the compound
• What does M+ peak indicate

  The molecular mass (Mr) of the compound

  
• How do you find the M+ peak


  it is the clear peak at the highest m/z value on the right hand side of the mass spectrum
• Reasoning for the existence of the M+1 peak (small peak after the M+ peak)


  exists because 1.1% of carbon is present as the carbon-13 isotope
• Fragmentation


  in mass spectrometry, some molecular ions break down into smaller fragments by this process
• Fragment ions


  ions formed from the breakdown of the molecular ion in a mass spectrometer
• How to use fragment ions to identify an organic molecule


  You are able to link different fragment ions together to form a moleculefragment ion peaks provide information (Mr) on the structure of the fragment(practise exam questions on these)
• Common fragment ions for m/z values of:15294357


  m/z of 15= CH3+m/z of 29= C2H5+m/z of 43= C3H7+m/z of 57= C4H9+
• Infrared radiation causes covalent bonds to...


  ...vibrate more and absorb energy
• Examples of greenhouse gases


  Carbon dioxide

  water vapour

  methane
• How is global warming caused as a result of greenhouse gases


  Greenhouse gases absorb IR that was re-emitted by the earth's surfaceeventually the vibrating bonds in these molecules re-emit this energy as radiation that increases the temperature of the atmosphere close to the surface of the earth
• Infrared Spectroscopy


  Used to determine chemical structure because different bonds will absorb different wavelengths of light.

  
• Fingerprint region


  An area of an infrared spectrum below 1500 cm-1 that gives a characteristic pattern for different compounds.

  
• What word describes the peak of an O-H bond in infrared specreoscopy


  Broad
• Infrared spectrum of a carboxylic acid


  Broad OH peak at 2500-3330Key C=O peak at 1630-1820

  
• Infrared spectrum of an aldehyde/ketone


  Key C=O peak at 1630 - 1820

  
• Applications of infrared spectroscopy


  Identify pollutants

  Breathalysers
• Identifying an unknown compound using what 3 methods?


  Elemental analysis

  Mass spectroscopy

  Infrared spectroscopy