Summary A Level Edexcel Chemistry Unit 7 - Modern Analytical Techniques I notes written by a 3A* Imperial College London Medicine Student

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7-Modern Analytical Techniques
Mass Spectrometry
Measuring Mr of an Organic Molecule
Fragmentation
Infrared Spectroscopy




Mass Spectrometry
Measuring Mr of an Organic
Molecule
Molecule - put through a mass spectrometer - will
break up and give a series of peaks caused by the
fragments.

The peak with the largest m/z (mass/charge ratio) -
due to the complete (not fragmented) molecule and
will be equal to the Mr of the molecule - parent ion
or molecular ion.

Sometimes M+1 peak - m/z value 1 more than the
molecular ion peak - caused by carbon-13 isotope.




7-Modern Analytical Techniques 1

, Fragmentation
When organic molecules are passed through a mass spectrometer - detects
both the whole molecule and fragments of the molecule.

Molecular ion formed: M → [M]+ + e−

The molecule loses an electron and becomes both an ion and a free radical.

Several peaks in the mass spectrum occur due to fragmentation (covalent bonds
breaking) - [M]+ → X+ + + Y−




Infrared Spectroscopy
Certain bonds in a molecule absorb infra-red radiation at characteristic
frequencies causing the covalent bonds to vibrate.

Spectra - provide information about the types of bonds present in a molecule.




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