8.1.6 Use of Tetramethylsilane (TMS)

• In NMR spectroscopy, Tetrametylsilane (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 is accounting 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

 ¹H NMR spectrum for TMS showing it’s signal at 0 ppm