A methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms — CH3. In formulas, the group is often abbreviated Me. Such hydrocarbon groups occur in many organic compounds. It is a very stable group in most molecules. While the methyl group is usually part of a larger molecule, it can be found on its own in any of three forms: anion, cation or radical. The anion has eight valence electrons, the radical seven and the cation six. All three forms are highly reactive and rarely observed.
1 Methyl cation, anion, and radical
1.1 Methyl cation 1.2 Methyl anion 1.3 Methyl radical
2.1 Oxidation 2.2 Methylation 2.3 Deprotonation 2.4 Free radical reactions
Methyl cation, anion, and radical Methyl cation The methylium cation (CH3+) exists in the gas phase, but is otherwise not encountered. Some compounds are considered to be sources of the CH3+ cation, and this simplification is used pervasively in organic chemistry. For example, protonation of methanol gives a strongly electrophilic methylating reagent:
CH3OH + H+ → CH3+ + H2O
Similarly, methyl iodide and methyl triflate are viewed as the
equivalent of the methyl cation because they readily undergo SN2
reactions by weak nucleophiles.
The methanide anion (CH3−) exists only in rarefied gas phase or
under exotic conditions. It can be produced by electrical discharge in
ketene at low pressure (less than one torr) and its enthalpy of
reaction is determined to be about 252.2±3.3 kJ/mol.
In discussions mechanisms of organic reactions, methyl lithium and
2 M + CH3X → MCH3 + MX
where M is an alkali metal.
Main article: Methyl radical
The methyl radical has the formula CH3. It exists in dilute gases, but
in more concentrated form it readily dimerizes to ethane. It can be
produced by thermal decomposition of only certain compounds,
especially those with an -N=N- linkage.
The reactivity of a methyl group depends on the adjacent substituents.
Methyl groups can be quite unreactive. For example, in organic
compounds, the methyl group resists attack by even the strongest
The oxidation of a methyl group occurs widely in nature and industry.
The oxidation products derived from methyl are CH2OH, CHO, and CO2H.
For example, permanganate often converts a methyl group to a carboxyl
(-COOH) group, e.g. the conversion of toluene to benzoic acid.
Ultimately oxidation of methyl groups gives protons and carbon
dioxide, as seen in combustion.
Main article: Methylation
Demethylation (the transfer of the methyl group to another compound)
is a common process, and reagents that undergo this reaction are
called methylating agents. Common methylating agents are dimethyl
sulfate, methyl iodide, and methyl triflate. Methanogenesis, the
source of natural gas, arises via a demethylation reaction.
Certain methyl groups can be deprotonated. For example, the acidity of
the methyl groups in acetone ((CH3)2CO) is about 1020 more acidic than
methane. The resulting carbanions are key intermediates in many
reactions in organic synthesis and biosynthesis. Fatty acids are
produced in this way.
Free radical reactions
When placed in benzylic or allylic positions, the strength of the C-H
bond is decreased, and the reactivity of the methyl group increases.
One manifestation of this enhanced reactivity is the photochemical
chlorination of the methyl group in toluene to give benzyl
^ March, Jerry (1992). Advanced organic chemistry: reactions,
mechanisms, and structure. John Wiley & Sons.
^ G. Barney Ellison , P. C. Engelking , W. C. Lineberger (1978), "An
experimental determination of the geometry and electron affinity of
methyl radical CH3" Journal of the American Chemical Society, volume
100, issue 8, pages 2556–2558. doi:10.1021/ja00476a054
^ Thauer, R. K., "
v t e
Only carbon, hydrogen and oxygen
Only one element apart from C, H, O
Disulfide Sulfone Sulfonic acid Sulfoxide Thial Thioester Thioether Thioketone Thiol
Selenol Selenonic acid Seleninic acid Selenenic acid
Isothiocyanate Phosphoramide Sulfenyl chloride Sulfonamide Thiocyanate
See also chemical classification, chemical nomenclature (inorgan