![Trimethylsilyl group](https://upload.wikimedia.org/wikipedia/commons/d/da/Trimethylsilyl_group.PNG)
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 rest ...
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 many ...
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 tab ...
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
Tetramethylsilane (abbreviated as TMS) is the organosilicon 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 ...
, 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
In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (— O H) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds are c ...
, 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. Carboxylic ...
s by substituting a trimethylsilyl group for a hydrogen in the
hydroxyl groups 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
Trimethylsilyl chloride, also known as chlorotrimethylsilane is an organosilicon compound (silyl halide), with the formula (CH3)3SiCl, often abbreviated Me3SiCl or TMSCl. It is a colourless volatile liquid that is stable in the absence of water. I ...
and
bis(trimethylsilyl)acetamide
Bis(trimethylsilyl)acetamide (BSA) is an organosilicon compound with the formula Me3SiNC(OSiMe3)Me (Me = CH3). It is a colorless liquid that is soluble in diverse organic solvents, but reacts rapidly with compounds, including solvents and moistu ...
. 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 use ...
. An example of such trimethylsilylation is mentioned in the
Brassicasterol 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
In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...
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 moder ...
or some other
chemical reaction
A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...
s.
In
chromatography
In chemical analysis, chromatography is a laboratory technique for the separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it through a system (a ...
, derivitization of accessible
silanol
A silanol is a functional group in silicon chemistry with the connectivity Si–O–H. It is related to the hydroxy functional group (C–O–H) found in all alcohols. Silanols are often invoked as intermediates in organosilicon ch ...
groups in a bonded
stationary phase with trimethylsilyl groups is referred to as
endcapping In chromatography, endcapping refers to the replacement of accessible silanol groups in a bonded stationary phase by trimethylsilyl groups. End-capped columns have much lower residual silanol group activity compared to non-endcapped columns. Endca ...
.
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 fie ...
, signals from atoms in trimethylsilyl groups in compounds will commonly have chemical shifts close to the
tetramethylsilane
Tetramethylsilane (abbreviated as TMS) is the organosilicon 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 ...
reference peak at 0 ppm. Also compounds, such as high temperature silicone "
stopcock"
grease, which have
polysiloxane
A silicone or polysiloxane is a polymer made up of siloxane (−R2Si−O−SiR2−, where R = organic group). They are typically colorless oils or rubber-like substances. Silicones are used in sealants, adhesives, lubricants, medicine, cooking ...
s (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 be ...
s.
Super silyl groups
![Tri(trimethylsilyl)silyl](https://upload.wikimedia.org/wikipedia/commons/6/61/Tri%28trimethylsilyl%29silyl.png)
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
In organic chemistry, butyl is a four-carbon alkyl radical or substituent group with general chemical formula , derived from either of the two isomers (''n''-butane and isobutane) of butane.
The isomer ''n''-butane can connect in two ways, givi ...
groups. The TTMSS group was proposed in 1993 by
Hans Bock. With a
van der Waals volume
The van der Waals radius, ''r'', of an atom is the radius of an imaginary hard sphere representing the distance of closest approach for another atom.
It is named after Johannes Diderik van der Waals, winner of the 1910 Nobel Prize in Physics, ...
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 for example in this
diastereoselective
In stereochemistry, diastereomers (sometimes called diastereoisomers) are a type of stereoisomer. Diastereomers are defined as non-mirror image, non-identical stereoisomers. Hence, they occur when two or more stereoisomers of a compound have dif ...
one-pot reaction
In chemistry a one-pot synthesis is a strategy to improve the efficiency of a chemical reaction whereby a reactant is subjected to successive chemical reactions in just one reactor. This is much desired by chemists because avoiding a lengthy sepa ...
involving two sequential
Mukaiyama aldol reaction
The Mukaiyama aldol addition is an organic reaction and a type of aldol reaction between a silyl enol ether and an aldehyde or formate. The reaction was discovered by Teruaki Mukaiyama (1927–2018) in 1973. His choice of reactants allows fo ...
s:
:
![Supersilylapplication](https://upload.wikimedia.org/wikipedia/commons/c/ce/Supersilylapplication.png)
TTMSS can also stand for tris(trimethylsilyl)silane, which is comparable as a chemical reagent to
tributyltin hydride
Tributyltin hydride is an organotin compound with the formula (C4H9)3SnH. It is a colorless liquid that is soluble in organic solvents. The compound is used as a source of hydrogen atoms in organic synthesis.
Synthesis and characterization
The c ...
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 bo ...
compounds. The reagent is employed in
radical reductions,
hydrosilylation Hydrosilylation, also called catalytic hydrosilation, describes the addition of Si-H bonds across unsaturated bonds."Hydrosilylation A Comprehensive Review on Recent Advances" B. Marciniec (ed.), Advances in Silicon Science, Springer Science, 2009 ...
and