Methyl group
Encyclopedia
Methyl group
Methyl group is a functional group derived from methane, containing one carbon atom bonded to three hydrogen atoms —CH3. The group is often abbreviated Me. Such hydrocarbon groups occur in many organic compounds. The methyl group can be found in three forms: anion, cation and radical. The anion...
is a functional group
Functional group
In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...
derived from methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
, containing one carbon atom bonded to three hydrogen atoms —CH3. The group is often abbreviated Me. Such hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
groups occur in many organic compounds. The methyl group can be found in three forms: anion, cation and radical
Radical (chemistry)
Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...
. The anion has eight valence electrons, the radical seven and the cation six. All three are highly reactive and rarely observed.
Methyl cation
The methylium cation (CH3+) exists in the gas phase, but is otherwise not encountered. Some compounds, are considered to be sources of "CH3+," 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
Triflate
Trifluoromethanesulfonate, also known by the trivial name triflate, is a functional group with the formula CF3SO3-. The triflate group is often represented by -OTf, as opposed to -Tf...
are viewed as the equivalent of the methyl cation because they readily undergo a SN2 reactions by weak nucleophile
Nucleophile
A nucleophile is a species that donates an electron-pair to an electrophile to form a chemical bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.Nucleophilic describes the...
s.
Methyl anion
The methanide anion (CH3-) similarly exists only under exotic conditions. In discussing mechanisms of organic reactions, it is often a useful simplification to consider methyl lithiumMethyl lithium
Methyllithium is an organolithium reagent with the empirical formula CH3Li. This s-block organometallic compound adopts an oligomeric structure both in solution and in the solid state. This highly reactive compound, invariably used as a solution in ethers, is a reagent in organic synthesis as well...
and related Grignard reagents as sal sources of "CH3-," although this view is fiction. Such reagents are generally prepared from the methyl halides:
- M + CH3X → MCH3
where M is alkali metal.
Methyl radical
The methyl radicalRadical (chemistry)
Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...
has the formula CH3. It exists in dilute gases, but in more concentrated form it readily dimerizes to ethane
Ethane
Ethane is a chemical compound with chemical formula C2H6. It is the only two-carbon alkane that is an aliphatic hydrocarbon. At standard temperature and pressure, ethane is a colorless, odorless gas....
. It can be produced by thermal decomposition of only certain compounds, especially those with an -N=N- linkage.
Reactivity
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 acidAcid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
s.
Oxidation
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, permanganatePermanganate
A permanganate is the general name for a chemical compound containing the manganate ion, . Because manganese is in the +7 oxidation state, the permanganate ion is a strong oxidizing agent. The ion has tetrahedral geometry...
often converts a methyl group to a carboxyl (-COOH) group, e.g. the conversion of toluene
Toluene
Toluene, formerly known as toluol, is a clear, water-insoluble liquid with the typical smell of paint thinners. It is a mono-substituted benzene derivative, i.e., one in which a single hydrogen atom from the benzene molecule has been replaced by a univalent group, in this case CH3.It is an aromatic...
to benzoic acid
Benzoic acid
Benzoic acid , C7H6O2 , is a colorless crystalline solid and the simplest aromatic carboxylic acid. The name derived from gum benzoin, which was for a long time the only source for benzoic acid. Its salts are used as a food preservative and benzoic acid is an important precursor for the synthesis...
. Ultimately oxidation of methyl groups gives protons and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, as seen in combustion.
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 dimethylsulfate, methyl iodide, and methyl triflateMethyl triflate
Methyl trifluoromethanesulfonate, is commonly called methyl triflate, and has the chemical formula CF3SO2-OCH3, and is used as a very powerful methylating reagent in chemistry....
. Methanogenesis, the source of natural gas, arises via a demethylation reaction.
Deprotonation
Certain methyl groups can be deprotonated. For example, the acidity of the methyl groups in acetoneAcetone
Acetone is the organic compound with the formula 2CO, a colorless, mobile, flammable liquid, the simplest example of the ketones.Acetone is miscible with water and serves as an important solvent in its own right, typically as the solvent of choice for cleaning purposes in the laboratory...
((CH3)2CO) is about 1020 more acidic than methane. The resulting carbanions are key intermediates in many reactions in organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
and biosynthesis
Biosynthesis
Biosynthesis is an enzyme-catalyzed process in cells of living organisms by which substrates are converted to more complex products. The biosynthesis process often consists of several enzymatic steps in which the product of one step is used as substrate in the following step...
. Fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
s arise in this way.
Free radical reactions
When placed in benzylic or allylic positions, the C-H bond strength 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 chlorideBenzyl chloride
Benzyl chloride, or α-chlorotoluene, is an organic compound with the formula C6H5CH2Cl. This colourless liquid is a reactive organochlorine compound that is a widely used chemical building block.-Preparation:...
.
Etymology
FrenchFrance
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
chemists Jean-Baptiste Dumas
Jean-Baptiste Dumas
Jean Baptiste André Dumas was a French chemist, best known for his works on organic analysis and synthesis, as well as the determination of atomic weights and molecular weights by measuring vapor densities...
and Eugene Peligot, after determining methanol's chemical structure, introduced "methylene" from the Greek methy = "wine" + hȳlē = "wood" (patch of trees) with the intention of highlighting its origins, "alcohol made from wood (substance)", but with Greek language errors: the Greek for "wood (substance)" is xylo-. The term "methyl" was derived in about 1840 by back-formation
Back-formation
In etymology, back-formation is the process of creating a new lexeme, usually by removing actual or supposed affixes. The resulting neologism is called a back-formation, a term coined by James Murray in 1889...
from "methylene", and was then applied to describe "methyl alcohol".
Methyl is the IUPAC nomenclature of organic chemistry
IUPAC nomenclature of organic chemistry
The IUPAC nomenclature of organic chemistry is a systematic method of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry . Ideally, every possible organic compound should have a name from which an unambiguous structural formula can be drawn. ...
term for an alkane
Alkane
Alkanes are chemical compounds that consist only of hydrogen and carbon atoms and are bonded exclusively by single bonds without any cycles...
(or alkyl) molecule, using the prefix "meth-" to indicate the presence of a single carbon.