Principles of NMR (AQA A Level Chemistry)
Revision Note
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)
Examiner Tips and Tricks
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:
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