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Tetramethylsilane is the chemical compound with the formula Si(CH3)4 or SiMe4 (Me = CH3). Commonly abbreviated TMS, it is the simplest tetraorganosilane. Like all silanes, the SiC4 framework is tetrahedral and consequently it is a non-polar. TMS is a building block in organometallic chemistry but also finds use in diverse applications.
Synthesis and reactions
TMS is a by-product of the production of methyl chlorosilanes, SiClx(CH3)4-x, via the "direct reaction" of methyl chloride with silicon. The more useful products of this reaction are those for x = 1, 2,and 3.
Uses in NMR spectroscopy
Tetramethylsilane is an internal standard for calibrating chemical shift in 1H, 13C and 29Si NMR spectroscopy. Because all twelve hydrogen atoms in a tetramethylsilane molecule are equivalent, the 1H NMR spectrum of TMS consists of a singlet. The chemical shift of this singlet is assigned as δ0.0 in the spectrum, and all other chemical shifts are determined relative to it. The silicon in tetramethylsilane shifts its 1H NMR signal upfield. The majority of compounds studied by 1H NMR have hydrogen peaks downfield of the tetramethylsilane peak, so there is usually no interference between the standard and the sample, and the tetramethylsilane singlet can usually easily be identified for the chemical shift calibration.
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 δ0.0 in the 13C spectrum, and all other chemical shifts are determined relative to it.
Because of its high volatility, TMS can easily be evaporated, which is convenient for recovery of samples analyzed by NMR spectroscopy.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Tetramethylsilane". A list of authors is available in Wikipedia.|