AQA A Level Chemistry

Revision Notes

7.10.1 Principles of NMR

Principles of NMR

  • Nuclear Magnetic Resonance (NMR) spectroscopy is used for analysing organic compounds
  • NMR analysis can provide information about the positions of 13C and 1H atoms in a molecule
  • All samples are measured against a reference compound – Tetramethylsilane (TMS)
    • TMS shows a single sharp peak on NMR spectra, at a value of zero
    • Sample peaks are then plotted as a ‘shift’ away from this reference peak
    • This gives rise to ‘chemical shift’ values for protons on the sample compound
    • Chemical shifts are measured in parts per million (ppm)

Exam Tip

You are often asked in exam questions why tetramethylsilane (TMS) is a suitable solvent for NMR analysis. Try to remember that TMS is:

  • Non toxic.
  • Does not react with the sample.
  • Easily separated from the sample molecule due to its low boiling point.
  • Produces one strong, sharp absorption peak on the spectrum.

Worked Example

Draw the structural formula of TMS

Answer:

Structural formula of TMS, downloadable AS & A Level Chemistry revision notes

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