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The trimethylsilyl group (–Si(CH3)3, abbreviated TMS) is a functional group in organic chemistry. This group consists of three methyl groups bonded to a silicon atom, which is in turn bonded to the rest of a molecule. This structural group is characterized by Chemically inert and a large molecular volume. Compounds with trimethylsilyl groups are not normally found in nature, but have applications in chemical synthesis and analysis.
Like other silyl protecting groups, the trimethylsilyl group acts as an ersatz Hydron. It is however much more bulky than a proton. The resulting steric effects can enable isolation of otherwise-reactive molecules, as observed in .
Trimethylsilyl forms strong bonds to in alcohols, phenols, or . The resulting Silyl ether groups −O-Si(CH3)3 shield such functional groups from pH variation, and participate in neither hydrogen bonding nor prototropic equilibria.
The reduced intermolecular forces between trimethylsilyloxy moeities make their parent compound more volatile. Trimethylsilated compounds are thus more amenable to gas-chromatographic or mass-spectrometric analysis. An example of trimethylsilylation for volatilization is mentioned in the Brassicasterol article. Such derivatizations are often done on a small scale in special .
In chromatography, endcapping is the process of covering a bonded stationary phase's accessible silanol groups with trimethylsilyl groups. The resulting columns are much less Acid and nonpolar.
In an NMR spectroscopy, signals from atoms in trimethylsilyl groups in compounds will commonly have chemical shifts close to the tetramethylsilane reference peak at 0 ppm. Also compounds, such as high temperature silicone "stopcock" Silicone grease, which have (often called silicones) in them will commonly show peaks from their methyl groups (attached to the silicon atoms) having NMR chemical shifts close to the tetramethylsilane standard peak, such as at 0.07 ppm in CDCl3.Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities. J. Org. Chem. 1997, 62( 21), pp 7512-7515.
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