Tetramethylsilane

Tetramethylsilane (TMS¹) is the simplest tetraalkylsilane and the organosilicon analogue of neopentane. It is a volatile liquid with a characteristic “organometallic” odor.

TMS has been known since at least 1911, when Artur Bygden at the University of Uppsala (Sweden) prepared it from silicon tetrachloride and the Grignard reagent² methylmagnesium chloride. Nowadays, TMS is made less expensively, as one of the products of the direct alkylation of elemental silicon with chloromethane.

TMS is sometimes used as a starting material for synthesizing more complex organosilanes, but its main use by far is as a versatile internal standard in NMR spectroscopy. Its ¹H, ¹³C, and ²⁹Si signals are sharp and have resonances that are distinctly different from the nuclei normally encountered in test samples.

For example, the ¹H atoms in TMS are highly shielded by the silicon atom and therefore resonate at a higher magnetic field than ¹H atoms surrounded by more common nuclei such as carbon, oxygen, and nitrogen. TMS is such a common standard that its ¹H chemical shift (δ) is defined as zero. In most ¹H spectra, all of the signals are to the left (lower field) of the TMS signal, although highly shielded protons in some aromatic compounds can appear to the right of TMS.

Highly soluble TMS is an ideal standard for generating NMR spectra of samples in organic solvents, but its low water solubility makes it unusable for aqueous samples. TMS’ low cost, chemical inertness, and ease of removal because of its volatility are additional factors that make it the universal standard for organic-solution NMR.

1. TMS is also used as the abbreviation for the trimethylsilyl radical.

2. Victor Grignard, the French Nobel Prize–winning chemist, had recently discovered the eponymous reaction; and chemists around the world were experimenting with alkylmagnesium halides in all sorts of ways.