Tetramethylsilane (TMS) & Deuterated Solvents (CIE A Level Chemistry)

Revision Note

Author

Expertise

Physics Lead

In NMR spectroscopy, tetramethylsilane (TMS) is used as a reference compound
The organic compound is dissolved in TMS before being introduced to the magnetic field of the spectrometer
It is an ideal chemical to use as a reference
- TMS is inert and volatile
- This reduces undesirable chemical reactions with the compound to be analysed
- It also mixes well with most organic compounds
TMS gives a single sharp peak on the NMR spectrum and is given a value of zero
The molecular formula of TMS is Si(CH₃)₄
- There are 12 hydrogens in this molecule
- All of the protons are in the same molecular environment. Therefore gives rise to just one peak
- This peak has a very high intensity as it accounts for the absorption of energy from 12 ¹H nuclei

Tetramethylsilane (TMS) – Si(CH₃)₄

When peaks are recorded from the sample compound, they are measured and recorded by their shift away from the sharp TMS peak
This gives rise to the chemical shift values for different ¹H environments in a molecule

Analytical Techniques - TMS 1H NMR, downloadable AS & A Level Chemistry revision notes

¹H NMR spectrum for TMS showing its signal at 0 ppm

When samples are analysed through NMR spectroscopy, they must be dissolved in a solvent
Tetramethylsilane (TMS) is a commonly used solvent in NMR
Despite TMS showing one sharp reference peak on NMR spectra, the proton atoms can still interfere with peaks of a sample compound
To avoid this interference, solvents containing deuterium can be used instead
- For example CDCl₃
- Deuterium (²H) is an isotope of hydrogen (¹H)
Deuterium nuclei absorb radio waves in a different region to the protons analysed in organic compounds
Therefore, the reference solvent peak will not interfere with those of the sample

to absolutely everything:

the (exam) results speak for themselves:

Did this page help you?