Trimethylsilyl
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A trimethylsilyl group (abbreviated TMS) is a functional group in organic chemistry. This group consists of three methyl groups bonded to a silicon atom [−Si(CH3)3], which is in turn bonded to the rest of a molecule.
A trimethylsilyl group bonded to a methyl group forms tetramethylsilane.
Compounds with trimethylsilyl groups are not normally found in nature. Chemists sometimes use a trimethylsilylating reagent to derivatize rather non-volatile compounds such as certain alcohols, phenols, or carboxylic acids by substituting a trimethylsilyl group for a hydrogen in the hydroxyl groups on the compounds. This way trimethylsiloxy groups are formed on the molecule. Trimethylsilyl groups on a molecule have a tendency to make it more volatile, often making the compounds more amenable to analysis by gas chromatography or mass spectrometry. Such derivatizations are often done on a small scale in special vials.
When attached to certain functional groups in a reactant molecule, trimethylsilyl groups may also be used as temporary blocking groups during chemical synthesis or some other chemical reactions.
In an NMR spectrum, signals from atoms in trimethylsilyl groups in compounds will commonly have chemical shifts close to the tetramethylsilane standard singlet peak. Also compounds, such as high temperature silicone "stopcock" grease, which have polysiloxanes (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.
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