The triphenylmethyl radical (often shorted to trityl radical) is an
organic compound with the formula (C
6H
5)
3C. It is a
persistent radical
In chemistry, a radical, also known as a free radical, is an atom, molecule, or ion that has at least one unpaired valence electron.
With some exceptions, these unpaired electrons make radicals highly chemically reactive. Many radicals spont ...
. It was the first
radical
Radical may refer to:
Politics and ideology Politics
*Radical politics, the political intent of fundamental societal change
*Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe and ...
ever to be described in
organic chemistry. Because of its accessibility, the trityl radical has been heavily exploited.
Preparation and properties
It can be prepared by
homolysis of
triphenylmethyl chloride 1 by a metal like
silver or
zinc in
benzene or
diethyl ether. The radical 2 forms a
chemical equilibrium with the
quinoid-type
dimer
Dimer may refer to:
* Dimer (chemistry), a chemical structure formed from two similar sub-units
** Protein dimer, a protein quaternary structure
** d-dimer
* Dimer model, an item in statistical mechanics, based on ''domino tiling''
* Julius Dimer ( ...
3 (
Gomberg's dimer
Gomberg's dimer is the organic compound with the formula Ph2C=C6H5-CPh3, where Ph = C6H5. It is a yellow solid that is air-stable for hours at room temperature and soluble in organic solvents. The compound achieved fame as the dimer of triphenylm ...
). In benzene the concentration of the radical is 2%.
Solutions containing the radical are
yellow; when the temperature of the solution is raised, the yellow color becomes more intense as the equilibrium is shifted in favor of the radical (in accordance with
Le Chatelier's principle
Le Chatelier's principle (pronounced or ), also called Chatelier's principle (or the Equilibrium Law), is a principle of chemistry used to predict the effect of a change in conditions on chemical equilibria. The principle is named after French c ...
).
When exposed to air, the radical rapidly oxidizes to the
peroxide, and the color of the solution changes from yellow to colorless. Likewise, the radical reacts with
iodine
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...
to triphenylmethyl iodide.
While the trityl radical forms a quinoid dimer, derivatives thereof with the appropriate substitution pattern do form dimers with a hexaphenylethane structure. X-ray studies give a bond length of 1.67 Å for hexakis(3,5-di-''t''-butylphenyl)ethane. Theoretical calculations on a very high level of theory indicate that
van der Waals attraction
In molecular physics, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and the ...
between the
''tert''-butyl groups create a potential minimum that is absent in the unsubstituted molecule. Other derivatives have been reported as the quinoid dimer
History
The radical was discovered by
Moses Gomberg in 1900 at the
University of Michigan. He tried to prepare
hexaphenylethane
Hexaphenylethane is a hypothetical organic compound consisting of an ethane core with six phenyl substituents. All attempts at its synthesis have been unsuccessful. The trityl free radical, Ph3C, was originally thought to dimerize to form hexap ...
from triphenylmethyl chloride and
zinc in
benzene in a
Wurtz reaction and found that the product, based on its behaviour towards iodine and oxygen, was far more reactive than anticipated. The discovered structure was used in the development of
ESR spectroscopy and confirmed by it.
The correct
quinoid structure for the dimer was suggested as early as 1904 but this structure was soon after abandoned by the scientific community in favor of
hexaphenylethane
Hexaphenylethane is a hypothetical organic compound consisting of an ethane core with six phenyl substituents. All attempts at its synthesis have been unsuccessful. The trityl free radical, Ph3C, was originally thought to dimerize to form hexap ...
(4). It subsequently took until 1968 for its rediscovery when researchers at the
Vrije Universiteit Amsterdam
The Vrije Universiteit Amsterdam (abbreviated as ''VU Amsterdam'' or simply ''VU'' when in context) is a public research university in Amsterdam, Netherlands, being founded in 1880. The VU Amsterdam is one of two large, publicly funded research ...
published
proton NMR data.
See also
*
Triphenylmethyl hexafluorophosphate
Triphenylmethyl (also triphenylcarbenium, trityl, or tritylium) hexafluorophosphate is an organic salt with the formula or , consisting of the triphenylmethyl cation and the hexafluorophosphate anion .
Triphenylmethyl hexafluorophosphate is a ...
*
Triphenylmethane
*
Triarylmethane dye
*
Trivalent group 14 radicals
A trivalent group 14 radical (also known as a ''trivalent tetrel radical'') is a molecule that contains a group 14 element (E = C, Si, Ge, Sn, Pb) with three bonds and a free radical, having the general formula of R3E•. Such compounds can be c ...
References
{{reflist, 2
External links
Molecule of the Month June 1997
Free radicals
Phenyl compounds