A trimethylsilyl group (abbreviated TMS) is a
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the r ...
in
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J ...
. This group consists of three
methyl
In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in ...
groups bonded to a
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...
atom
3)3">minus;Si(CH3)3 which is in turn bonded to the rest of a molecule. This structural group is characterized by
chemical inertness and a large
molecular volume, which makes it useful in a number of applications.
A trimethylsilyl group bonded to a methyl group forms
tetramethylsilane, which is abbreviated as TMS as well.
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 acid
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxyli ...
s by substituting a trimethylsilyl group for a hydrogen in the
hydroxyl group
In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...
s on the compounds. This way
trimethylsiloxy groups
3)3">minus;O-Si(CH3)3are formed on the molecule. A couple of examples of trimethylsilylating agents include
trimethylsilyl chloride and
bis(trimethylsilyl)acetamide. 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
Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a '' mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is u ...
. An example of such trimethylsilylation is mentioned in the
Brassicasterol
Brassicasterol (24-methyl cholest-5,22-dien-3β-ol) is a 28- carbon sterol synthesised by several unicellular algae ( phytoplankton) and some terrestrial plants, like rape. This compound has frequently been used as a biomarker for the presence of ...
article. Such derivatizations are often done on a small scale in special
vial
A vial (also known as a phial or flacon) is a small glass or plastic vessel or bottle, often used to store medication as liquids, powders or capsules. They can also be used as scientific sample vessels; for instance, in autosampler devices i ...
s.
When attached to certain functional groups in a
reactant molecule, trimethylsilyl groups may also be used as temporary
protecting groups during
chemical synthesis
As a topic of chemistry, chemical synthesis (or combination) is the artificial execution of chemical reactions to obtain one or several products. This occurs by physical and chemical manipulations usually involving one or more reactions. In mod ...
or some other
chemical reaction
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking ...
s.
In
chromatography, derivitization of accessible
silanol groups in a bonded
stationary phase with trimethylsilyl groups is referred to as
endcapping.
In an
NMR spectrum
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique to observe local magnetic fields around atomic nuclei. The sample is placed in a magnetic fiel ...
, 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"
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, such as at 0.07 ppm in CDCl
3.
Otherwise very reactive molecules can be isolated when enveloped by bulky trimethylsilyl groups. This effect can be observed in
tetrahedrane
Tetrahedrane is a hypothetical platonic hydrocarbon with chemical formula and a tetrahedral structure. The molecule would be subject to considerable angle strain and has not been synthesized as of 2021. However, a number of derivatives have b ...
s.
Super silyl groups
Related to trimethylsilyl groups are "super" silyl groups of which there exist two varieties: A silicon group connected to three trimethylsilyl groups makes a tri(trimethylsilyl)silyl group (TTMSS or TMS
3Si) and a silicon group connected to three
tert-butyl groups. The TTMSS group was proposed in 1993 by
Hans Bock. With a
van der Waals volume of up to 7 cubic
angstrom
The angstromEntry "angstrom" in the Oxford online dictionary. Retrieved on 2019-03-02 from https://en.oxforddictionaries.com/definition/angstrom.Entry "angstrom" in the Merriam-Webster online dictionary. Retrieved on 2019-03-02 from https://www.m ...
it surpasses the related
TIPS group (around 2) and one potential application is its use as a temporary substituent promoting
asymmetric induction
In stereochemistry, asymmetric induction (also enantioinduction) describes the preferential formation in a chemical reaction of one enantiomer or diastereoisomer over the other as a result of the influence of a chiral feature present in the su ...
for example in this
diastereoselective one-pot reaction involving two sequential
Mukaiyama aldol reactions:
:
TTMSS can also stand for tris(trimethylsilyl)silane, which is comparable as a chemical reagent to
tributyltin hydride without the associated toxicity concern of
organotin and
tributyltin
Tributyltin (TBT) is an umbrella term for a class of organotin compounds which contain the (C4H9)3 Sn group, with a prominent example being tributyltin oxide. For 40 years TBT was used as a biocide in anti-fouling paint, commonly known as bott ...
compounds. The reagent is employed in
radical reductions,
hydrosilylation and