 | |
| Names | |
|---|---|
| IUPAC name Methyl[1] | |
| Identifiers | |
3D model (JSmol) | |
| 1696831 | |
| ChEBI | |
| ChemSpider |
|
| 57 | |
| MeSH | Methyl+radical |
| UNII | |
| |
| |
| Properties | |
| CH3 | |
| Molar mass | 15.035 g·mol−1 |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Methyl radical is anorganic compound with thechemical formulaCH•
3 (also written as[CH
3]•). It is a metastable colourless gas, which is mainly producedin situ as a precursor to other hydrocarbons in the petroleum cracking industry. It can act as either a strongoxidant or a strongreductant, and is quite corrosive to metals.
Its first ionization potential (yielding themethenium ion,CH+
3) is9.837±0.005 eV.[2]
The carbon centre in methyl can bond with electron-donating molecules by reacting:
Because of the capture of the nucleophile (R•), methyl has oxidising character. Methyl is a strong oxidant with organic chemicals. However, it is equally a strong reductant with chemicals such as water. It does not form aqueous solutions, as it reduces water to producemethanol and elemental hydrogen:
Themolecular geometry of the methyl radical istrigonal planar (bond angles are 120°), although the energy cost of distortion to apyramidal geometry is small. All other electron-neutral, non-conjugated alkyl radicals are pyramidalized to some extent, though with very small inversion barriers. For instance, thet-butyl radical has a bond angle of 118° with a 0.7 kcal/mol (2.9 kJ/mol) barrier topyramidal inversion. On the other hand, substitution of hydrogen atoms by more electronegative substituents leads to radicals with a strongly pyramidal geometry (112°), such as thetrifluoromethyl radical,CF•
3, with a much more substantial inversion barrier of around 25 kcal/mol (100 kJ/mol).[3]
Methyl undergoes the typical chemical reactions of a radical. Below approximately 1,100 °C (1,400 K), it rapidly dimerises to formethane. Upon treatment with an alcohol, it converts tomethane and either an alkoxy or hydroxyalkyl. Reduction of methyl gives methane. When heated above, at most, 1,400 °C (1,700 K), methyl decomposes to producemethylidyne and elemental hydrogen, or to producemethylene and atomic hydrogen:
Methyl is very corrosive to metals, forming methylated metal compounds:
Someradical SAM enzymes generate methyl radicals by reduction of S-adenosylmethionine.[4]
It can be produced by the ultraviolet photodissociation ofacetone vapour at 193 nm:[5]
It is also produced by the ultraviolet dissociation ofhalomethanes:
It can also be produced by the reaction ofmethane with thehydroxyl radical:
This process begins the major removal mechanism of methane from the atmosphere. The reaction occurs in thetroposphere orstratosphere. In addition to being the largest known sink for atmospheric methane, this reaction is one of the most important sources of water vapor in the upper atmosphere.
This reaction in thetroposphere gives a methane lifetime of 9.6 years. Two more minor sinks are soil sinks (160 year lifetime) and stratospheric loss by reaction with•OH,•Cl and•O1D in the stratosphere (120 year lifetime), giving a net lifetime of 8.4 years.[6]
Methyl radicals can also be obtained bypyrolysis ofazomethane, CH3N=NCH3, in a low-pressure system.
Methyl was discovered ininterstellar medium in 2000 by a team led by Helmut Feuchtgruber who detected it using theInfrared Space Observatory. It was first detected in molecular clouds toward the centre of the Milky Way.[7]
