Tetramethylsilane

Tetramethylsilane
IUPAC name	tetramethylsilane
Other names	TMS
Identifiers
CAS number	75-76-3 Y
RTECS number	VV5705400
SMILES	C[Si](C)(C)C
Properties
Molecular formula	C4H12Si
Molar mass	88.22 g/mol
Appearance	Colourless liquid.
Density	0.648 g/cm-3, liquid.
Melting point	-99.06 °C (174.09 K)
Boiling point	26.6 °C (299.75 K)
Solubility in water	low
Structure
Molecular shape	Tetrahedral
Dipole moment	0 D
Hazards
R-phrases	R20, R36, R37, R38.
S-phrases	S16, S24/25, S7/9.
NFPA 704	4 3 0
Flash point	-28 °C
Related compounds
Related compounds	silane neopentane isobutane hexamethyldisiloxane
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Tetramethylsilane (abbreviated as TMS) is the chemical compound with the formula Si(CH₃)₄. It is the simplest tetraorganosilane. Like all silanes, the TMS framework is tetrahedral. TMS is a building block in organometallic chemistry but also finds use in diverse niche applications.

Synthesis and reactions

TMS is a by-product of the production of methyl chlorosilanes, SiCl_x(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.^[1]

TMS undergoes deprotonation upon treatment with butyl lithium to give (H₃C)₃SiCH₂Li. The latter, trimethylsilylmethyl lithium, is a relatively common alkylating agent.

In chemical vapor deposition, TMS is the precursor to silicon dioxide or silicon carbide, depending on the deposition conditions.

Uses in NMR spectroscopy

Tetramethylsilane is an internal standard for calibrating chemical shift for ¹H, ¹³C and ²⁹Si 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 δ0.0, 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.

Routine NMR spectra are not always now referenced to TMS, in which case residual solvent peaks may be used to calibrate against. Residual solvent may either remain from synthetic procedures, or as traces of non-deuterated material in the NMR solvent itself. As values for common reference peaks have now been well determined, the addition of TMS is no longer a necessity for commercial NMR solvents.

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.

References

1. ^ Elschenbroich, C. ”Organometallics” (2006) Wiley-VCH: Weinheim. ISBN 978-3-29390-6