Spectroscopy

Spectroscopy

1. Mass Spectroscopy

   • Molecular ion peak
     • Furthest right hand side clear peak
     • Represents m/z value and molecular mass of the molecule
     • M+1 peak- small peak after M+ peak, accounts for (1.1%)13C isotope
       • Other peaks after M+ indicate isotopes too e.g Cl
     • M+ peak
   • Fragmentation
     • Molecular ion breaks into
       • Positive fragment ion
         • Detected by mass spec
       • Radical
         • Not detected by mass spec
     • Helps tell isomers apart as ions will fragment in different ways depending on structure
     • Base peak- tallest peak, bonds that break the most often
   • Oragnic compound loses electron, forms positive molecular ion. Mass to charge ratio detected. Charge = +1 so this ratio = Mr.

2. Infra-Red Spectroscopy

   • Cov. bonds vibrate at same frequency as IR meaning they absorb it and....
     • Bend- change in bond angle
     • Stretch- rhythmatic movement, increasing or decreasing distance between atomic centres
   • Global warming
     • Most of suns radiation absorbed by earth's surface, some re-emitted as longer wavelength IR
       • H2O, CO2, CH4 absorb this ( bonds same Hz as radiation), eventually the vibrating bonds in these molecules re-emit this radiation
         • Leads to a rise in temperature
   • Identifies functional group
   • How it works
     • Beam of IR radiation passed through sample
       • Molecule absorbs some IR frequencies, emerging beam analysed to determine absorbed Hz
         • IR spec connected to a computer, plots graph of transmittance against wave number
   • Applications
     • Testing vehicle emissions to monitor localised pollution
     • Breathalysers

3. Order of analysis

   • Elemental - % data composition to determine empirical formula
     • Mass Spectroscopy- M+ peak determines Mr, fragment ions to indicate structure
       • IR spec- Identify bonds and functional groups

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