Tetramethylsilane (abbreviated as TMS) is the
organosilicon compound with the
formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...
Si(CH
3)
4. It is the simplest tetraorganosilane. Like all
silanes, the TMS framework is tetrahedral. TMS is a building block in
organometallic chemistry
Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...
but also finds use in diverse niche applications.
Synthesis and reactions
TMS is a by-product of the production of methyl chlorosilanes, SiCl
''x''(CH
3)
4−''x'', via the
direct process of reacting
methyl chloride
Chloromethane, also called methyl chloride, Refrigerant-40, R-40 or HCC 40, is an organic compound with the chemical formula . One of the haloalkanes, it is a colorless, sweet-smelling, flammable gas. Methyl chloride is a crucial reagent in indus ...
with silicon. The more useful products of this reaction are those for ''x'' = 1 (
trimethylsilyl chloride), 2 (
dimethyldichlorosilane), and 3 (
methyltrichlorosilane).
TMS undergoes deprotonation upon treatment with
butyllithium to give
(H3C)3SiCH2Li. The latter, trimethylsilylmethyl lithium, is a relatively common
alkylating agent.
In
chemical vapor deposition
Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high-quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films.
In typical CVD, the wafer (electro ...
, TMS is the precursor to
silicon dioxide
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...
or
silicon carbide
Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A wide bandgap semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder a ...
, depending on the deposition conditions. In the formation of silicon carbide,
carbosilanes, such as
1,3,5,7-tetramethyl-1,3,5,7-tetrasilaadamantane, are observed as intermediates.
Uses in NMR spectroscopy
Tetramethylsilane is the accepted internal standard for calibrating
chemical shift
In nuclear magnetic resonance (NMR) spectroscopy, the chemical shift is the resonant frequency of an atomic nucleus relative to a standard in a magnetic field. Often the position and number of chemical shifts are diagnostic of the structure of ...
for
1 H,
13 C and
29 Si NMR spectroscopy in organic solvents (where TMS is soluble). In water, where it is not soluble, sodium salts of DSS,
2,2-dimethyl-2-silapentane-5-sulfonate, are used instead. Because of its high volatility, TMS can easily be evaporated, which is convenient for recovery of samples analyzed by NMR spectroscopy.
Because all twelve hydrogen atoms in a tetramethylsilane molecule are equivalent, its
1H NMR spectrum consists of a singlet.
The chemical shift of this singlet is assigned as ''δ'' 0, and all other chemical shifts are determined relative to it. The majority of compounds studied by
1H NMR spectroscopy absorb downfield of the TMS signal, thus there is usually no interference between the standard and the sample. Similarly, all four carbon atoms in a tetramethylsilane molecule are equivalent.
In a fully decoupled
13C NMR spectrum, the carbon in the tetramethylsilane appears as a singlet, allowing for easy identification. The chemical shift of this singlet is also set to be ''δ'' 0 in the
13C spectrum, and all other chemical shifts are determined relative to it.
References
{{Authority control
Carbosilanes
Trimethylsilyl compounds