A methyl group
is an alkyl
derived from methane
, containing one carbon
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
. The anion has eight valence electrons, the radical seven and the cation six. All three forms are highly reactive and rarely observed.
Methyl cation, anion, and radical
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 nucleophile
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
.G. Barney Ellison , P. C. Engelking , W. C. Lineberger (1978), "An experimental determination of the geometry and electron affinity of methyl radical " Journal of the American Chemical Society, volume 100, issue 8, pages 2556–2558.
In discussions mechanisms of organic reactions, methyl lithium
and related Grignard reagents
are often considered to be salts of "CH3−"; and though the model may be useful for description and analysis, it is only a useful fiction. Such reagents are generally prepared from the methyl halides:
2 M + CH3X → MCH3 + MX
where M is an alkali metal.
The methyl radical
has the formula CH3. It exists in dilute gases, but in more concentrated form it readily dimer
izes 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 substituent
s. Methyl groups can be quite unreactive. For example, in organic compounds, the methyl group resists attack by even the strongest acid
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 proton
s and carbon dioxide
, as seen in combustion.
Demethylation (the transfer of the methyl group to another compound) is a common process, and reagent
s that undergo this reaction are called methylating agents. Common methylating agents are dimethyl sulfate
, methyl iodide
, and methyl triflate
, the source of natural gas, arises via a demethylation reaction.Thauer, R. K., "Biochemistry of Methanogenesis: a Tribute to Marjory Stephenson", Microbiology, 1998, volume 144, pages 2377–2406.
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 carbanion
s are key intermediates in many reactions in organic synthesis
. Fatty acid
s are produced in this way.
Free radical reactions
When placed in benzylic
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 chloride
.M. Rossberg et al. “Chlorinated Hydrocarbons” in Ullmann’s Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim.
In the special case where one hydrogen is replaced by deuterium
(D) and another hydrogen by tritium
(T), the methyl substituent becomes chiral
.http://www2.lsdiv.harvard.edu/labs/evans/pdf/smnr_2000-2001_Burch_Jason.pdf Methods exist to produce optically pure methyl compounds, e.g., chiral acetic acid
(CHDTCO2H). Through the use of chiral methyl groups, the stereochemical
course of several biochemical
transformations have been analyzed.Heinz G. Floss, Sungsook Lee "Chiral methyl groups: small is beautiful" Acc. Chem. Res., 1993, volume 26, pp 116–122.
chemists Jean-Baptiste Dumas
and Eugene Peligot
, after determining methanol's chemical structure, introduced "methylene" from the Greek methy
"wine" and hȳlē
"wood, patch of trees" with the intention of highlighting its origins, "alcohol made from wood (substance)".J. Dumas and E. Péligot (1835) "Mémoire sur l'espirit de bois et sur les divers composés ethérés qui en proviennent" (Memoir on spirit of wood and on the various ethereal compounds that derive therefrom), Annales de chimie et de physique
: 5-74; from page 9
: Nous donnerons le nom de méthylène (1) à un radical … (1) μεθυ, vin, et υλη, bois; c'est-à-dire vin ou liqueur spiritueuse du bois.
(We will give the name "methylene" (1) to a radical … (1) methy, wine, and hulē, wood; that is, wine or spirit of wood.)Note that the correct Greek word for the substance "wood" is xylo-
. The term "methyl" was derived in about 1840 by back-formation
from "methylene", and was then applied to describe "methyl alcohol".
is the IUPAC nomenclature of organic chemistry
term for an alkane
(or alkyl) molecule, using the prefix "meth-" to indicate the presence of a single carbon.