IR Spectroscopy

  • Beam of IR radiation passed through sample
  • It is absorbed by covalent bonds, increasing energy
  • Bonds between other atoms absorb different frequencies of IR
  • Frequencies where IR is absorbed are plotted to give IR spectrum
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Practical Use of IR

Person suspected of drink driving


Amount of ethanol found by measuring intensity of peak of C-H bond on IR spectrum

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Mass Spectroscopy

Common Fragment Ions

Fragment                  m/z

CH3+                             15

CH2CH3+                      29

CH2CH2CH3+              43

OH+                              17

C=O+                            28

COCH3+                       43

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Mass Spectroscopy

M peak is the peak with highest mass/charge ratio

m/z value is the molecular mass of compound

Applications of Mass Spectroscopy

  • Measure levels of pollutants present in environment
  • Probes on Mars studying elements/compounds that may lead to suggesting life existed
  • Measure amount of pesticides entering food chain

Differentiating between similar molecules

They don't produce the exact same fragments

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