Return to site

A2/ A-level Chemistry: Combined techniques

Mass spectrometry, Infrared spectroscopy, NMR

April 28, 2022

Mass spectrometry

  • In A2/A-Level Chemistry, M+ ion m/z is equal to molecular mass (combine with give empirical formula to deduce molecular formula)
  • Identify key fragment peaks to deduce part of the structure of the molecule

Fragment ion

M/z value

CH3+

17

CH2CH3+

29

CH2CH2CH3+ or CH3CO+

43

CH2CH2CH2CH3+

57

OH+

17

C6H4CH3+ or C6H3(CH2)2+ (aromatic)

91

Infrared spectroscopy

In A2/A-Level Chemistry,

  • Use characteristic adsorptions to identify functional groups in the molecule

13C-NMR

  • In A2/A-Level Chemistry, Number of peaks --> number of different carbon environments
  • Chemical shift --> type of carbon environment

1H-NMR

  • In A2/A-Level Chemistry, Number of peaks --> number of different hydrogen environments
  • Chemical shift --> type of hydrogen environment
  • Splitting pattern --> n+1 hydrogens on the adjacent carbon
  • Relative peak area --> number of hydrogens in each environment
  • D2O--> Peaks that disappear are either –OH or –NH (because the deuterium exchanges with the present hydrogen atom

That's the end~