Methyl radical
From Wikipedia, the free encyclopedia
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| Names | |
|---|---|
| IUPAC name
Methyl[1] | |
| Identifiers | |
3D model (JSmol) |
|
| 1696831 | |
| ChEBI | |
| ChemSpider | |
| 57 | |
| MeSH | Methyl+radical |
PubChem CID |
|
| UNII | |
CompTox Dashboard (EPA) |
|
| |
| |
| Properties | |
| CH3 | |
| Molar mass | 15.035 g·mol−1 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
Methyl radical is an organic compound with the chemical formula CH•
3 (also written as [CH
3]•). It is a metastable colourless gas, which is mainly produced in situ as a precursor to other hydrocarbons in the petroleum cracking industry. It can act as either a strong oxidant or a strong reductant, and is quite corrosive to metals.
Redox behaviour
Its first ionization potential (yielding the methenium ion, CH+
3) is 9.837±0.005 eV.[2]
The carbon centre in methyl can bond with electron-donating molecules by reacting:
- CH•
3 + R• → RCH
3
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 produce methanol and elemental hydrogen:
- 2 CH•
3 + 2 H
2O → 2 CH
3OH + H
2
Structure
The molecular geometry of the methyl radical is trigonal planar (bond angles are 120°), although the energy cost of distortion to a pyramidal geometry is small. All other electron-neutral, non-conjugated alkyl radicals are pyramidalized to some extent, though with very small inversion barriers. For instance, the t-butyl radical has a bond angle of 118° with a 0.7 kcal/mol (2.9 kJ/mol) barrier to pyramidal inversion. On the other hand, substitution of hydrogen atoms by more electronegative substituents leads to radicals with a strongly pyramidal geometry (112°), such as the trifluoromethyl radical, CF•
3, with a much more substantial inversion barrier of around 25 kcal/mol (100 kJ/mol).[3]
Chemical reactions
Methyl undergoes the typical chemical reactions of a radical. Below approximately 1,100 °C (1,400 K), it rapidly dimerises to form ethane. Upon treatment with an alcohol, it converts to methane 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 produce methylidyne and elemental hydrogen, or to produce methylene and atomic hydrogen:
- CH•
3 → CH• + H
2 - CH•
3 → CH•
2 + H•
Methyl is very corrosive to metals, forming methylated metal compounds:
- M + n CH•
3 → M(CH3)n
