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Organic Spectroscopy

Organic Spectroscopy. A range of techniques infra-red, mass spectrometry and proton NMR are used to determine the structure of chemical compounds and to identify the components in mixtures. These techniques are commonly used in.

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Organic Spectroscopy

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  1. Organic Spectroscopy A range of techniques infra-red, mass spectrometry and proton NMR are used to determine the structure of chemical compounds and to identify the components in mixtures.

  2. These techniques are commonly used in • The pharmaceutical industry and medicinal chemistry (research and development, quality control etc). • The oil industry to identify organic compounds. • Government labs to check contaminates in foodstuff, pollutants in water and drugs. • Research laboratories to study larger fragments of DNA and proteins in biological samples.

  3. Mass spectrometry Mass spectrometry is used by chemists to determine the accurate molecular mass and structural features of an organic compound. Photographer Dr R Campbell

  4. Mass spectrometry

  5. Principles of Mass Spectrometry Author Kermit Murray

  6. Sample In mass spectrometry the sample is first vaporised and held in a vacuum to reduce collisions.

  7. Ion source The sample is then ionised • The vaporised sample is bombarded with electrons. • The high energy electrons knock out electrons from the sample to form ions. • Positive ions are produced called molecular ions. M → [M]+ (molecule) (molecular ion)

  8. Fragmentation The resulting molecular (parent) ions is generally unstable and therefore may break up to produce daughter ions.

  9. Mass Analyser • The ions are focussed into a fast ion beam by passing through focussing slits. • The stream of ions is passed through a magnetic field. • The ions are deflected by the field and sorted by their mass to charge ratio.

  10. Detector • Ions with same mass to charge ratio (m/z) will have the same trajectory. • They are counted by the detector. • As the magnetic field strength is changed, ions with different m/z ratios will be detected so that a graph of abundance can be produced.

  11. Mass spectrum benzoic acid

  12. Interpreting mass spectrum The molecular ion is the most important peak in a mass spectrum. It is formed by the loss of a single electron and therefore gives the molecular weight (formula mass) of the compound.

  13. Mass spectrum benzoic acid Molecular ion [M]+ Benzoic acid Formula mass 122

  14. Interpreting mass spectrum • The ion with the greatest abundance is called the base peak and is assigned an abundance of 100% • The other peaks represent the daughter ions.

  15. Mass spectrum benzoic acid Base peak Daughter ions

  16. Analysis of fragmentation The fragmentation pattern can also be used to gain structural information (functional groups present).

  17. Example 1 Benzoic acid

  18. Mass spectrum benzoic acid Molecular ion [M]+

  19. Mass spectrum benzoic acid Daughter ion [C7H5O]+ m/z = 105

  20. Mass spectrum benzoic acid Daughter ion [C6H5]+ m/z = 77

  21. Mass spectrum benzoic acid Daughter ion [C4H3]+ m/z = 51

  22. Example 2 Methyl benzoate

  23. Mass spectrum methyl benzoate Molecular ion [M]+

  24. Mass spectrum methyl benzoate Daughter ion [C7H5O]+ m/z = 105

  25. Mass spectrum methyl benzoate Daughter ion [C6H5]+ m/z = 77

  26. Mass spectrum methyl benzoate Daughter ion [C4H3]+ m/z = 51

  27. Analysis • The mass spectrum of a organic compound is like a fingerprint for a particular compound. • Many types of mass spectrometer will automatically compare the mass spectrum of a compound against a known data base to allow identification.

  28. Analysis Mass spectrometers are used in airports to detect traces of explosives, narcotics. Operators collect trace residue by swabbing surfaces to be analysed.

  29. Mars Curiosity Rover A miniaturised gas chromatography mass spectrometer was used to separate and analyse compounds. Author NASA

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