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A methyl group is an
alkyl In organic chemistry, an alkyl substituent is an alkane missing one hydrogen. The term alkyl is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of C''n''H2''n''+1. A cycloalkyl is derived ...
derived from
methane Methane ( or ) is a chemical compound with the chemical formula (one atom of carbon and four atoms of hydrogen). It is a group-14 hydride and the simplest alkane, and is the main constituent of natural gas. The relative abundance of methane on ...
, containing one
carbon Carbon (from la, carbo "coal") is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Car ...
atom bonded to three
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. With a standard atomic weight of , hydrogen is the lightest element in the periodic table. Hydrogen is the most abundant chemical substance in the universe, constitut ...

hydrogen
atoms — CH3. In
formulas In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a chemical formula. The informal use of the term ''formula'' in science refers to the general construct of a relationship between given ...
, the group is often
abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full version of the word or phrase; for example, the word ''abbrevia ...
Me. Such
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons from which one hydrogen atom has been removed are functional groups called hydrocarb ...
groups occur in many
organic compounds , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organi ...
. It is a very stable group in most molecules. While the methyl group is usually part of a larger
molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. Molecules are distinguished ...
, it can be found on its own in any of three forms:
anion An ion () is a particle, atom or molecule with a net electrical charge. The charge of the electron is considered negative by convention. The negative charge of an ion is equal and opposite to charged proton(s) considered positive by convent ...
,
cation An ion () is a particle, atom or molecule with a net electrical charge. The charge of the electron is considered negative by convention. The negative charge of an ion is equal and opposite to charged proton(s) considered positive by convent ...
or
radical Radical may refer to: Arts and entertainment Music *''Radical'' (mixtape), by Odd Future, 2010 *''Radical'' (Smack album), 1988 *"Radicals", a song by Tyler, The Creator from the 2011 album ''Goblin'' Architecture and design * Radical period (d ...
. 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


Methyl cation

The methylium cation () exists in the
gas phase In the physical sciences, a phase is a region of space (a thermodynamic system), throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, magnetization and ...
, but is otherwise not encountered. Some compounds are considered to be sources of the cation, and this simplification is used pervasively in organic chemistry. For example,
protonation In chemistry, protonation (or hydronation) is the addition of a proton (or hydron, or hydrogen cation), (H+) to an atom, molecule, or ion, forming the conjugate acid. (The complementary process, when a proton is removed from a Brønsted–Lowry acid ...
of methanol gives an electrophilic methylating reagent that reacts by the SN2 pathway: :CH3OH + H+ → Similarly,
methyl iodide Iodomethane, also called methyl iodide, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one hyd ...
and methyl
triflate Triflate, also known by the systematic name trifluoromethanesulfonate, is a functional group with the formula CF3SO3−. The triflate group is often represented by −OTf, as opposed to −Tf (triflyl). For example, ''n''-butyl triflate can be writ ...

triflate
are viewed as the equivalent of the methyl cation because they readily undergo SN2 reactions by weak
nucleophile In chemistry, a nucleophile is a chemical species that forms bonds with electrophiles by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate ele ...
s.


Methyl anion

The methanide anion () exists only in rarefied gas phase or under exotic conditions. It can be produced by electrical discharge in
ketene A ketene is an organic compound of the form R′R″C=C=O, where R and R' are two arbitrary monovalent chemical groups (or two separate substitution sites in the same molecule). The name may also refer to the specific compound ethenone , the simple ...
at low pressure (less than one
torr The torr (symbol: Torr) is a unit of pressure based on an absolute scale, defined as exactly of a standard atmosphere (). Thus one torr is exactly (≈ ). Historically, one torr was intended to be the same as one "millimeter of mercury", ...
) and its
enthalpy of reaction The standard enthalpy of reaction (denoted \Delta H_^\ominus or \Delta H_^\ominus) is the difference between total reactant and total product enthalpies due to a chemical reaction, from reactants in their standard states to products in their standar ...
is determined to be about .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. It is a powerful
superbase A superbase is a compound that has a high affinity for protons. Superbases are valuable in organic chemistry, which abounds in very weak acids. Reactions involving superbases often require special techniques since they're easily destroyed by wat ...
; only the
lithium monoxide anion Lithium monoxide anion (LiO−) is a superbase existing in the gas phase. It was the strongest known base until 2008, when the isomeric diethynylbenzene dianions were determined to have a higher proton affinity. ''Ortho''-diethynylbenzene dianion i ...
() and the
diethynylbenzene dianion In organic chemistry, a diethynylbenzene dianion is a structure consisting of two ethynyl anions as substituents on a benzene ring. With the chemical formula , three positional isomers are possible, differing in the relative positions of the two su ...
s are known to be stronger. In discussing mechanisms of organic reactions,
methyl lithium Methyllithium is the simplest 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 s ...
and related
Grignard reagentsGrignard is a surname of French origin. People with that name include: * Ferre Grignard (193982), Belgian skiffle-singer ** ''Ferre Grignard'' (1972 album) * Georges Grignard (190577), French racing driver * Pierre Grignard (active 191820), Belgian ...
are often considered to be salts of ""; 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.


Methyl radical

The methyl
radical Radical may refer to: Arts and entertainment Music *''Radical'' (mixtape), by Odd Future, 2010 *''Radical'' (Smack album), 1988 *"Radicals", a song by Tyler, The Creator from the 2011 album ''Goblin'' Architecture and design * Radical period (d ...
has the formula . It exists in dilute gases, but in more concentrated form it readily dimerizes to
ethane Ethane ( or ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petroche ...
. It can be produced by
thermal decomposition Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is require ...
of only certain compounds, especially those with an –N=N– linkage.


Reactivity

The reactivity of a methyl group depends on the adjacent
substituent A substituent is one or a group of atoms that replaces (one or more) hydrogen atoms on the parent chain of a hydrocarbon, thereby becoming a moiety in the resultant (new) molecule. (In organic chemistry and biochemistry, the terms ''substituent'' ...
s. Methyl groups can be quite unreactive. For example, in organic compounds, the methyl group resists attack by even the strongest
acid An acid is a molecule or ion capable of donating a proton (hydrogen ion H+) (a Brønsted–Lowry acid), or, alternatively, capable of forming a covalent bond with an electron pair (a Lewis acid). The first category of acids are the proton do ...
s.


Oxidation

The
oxidation (mild reducing agent) are added to powdered potassium permanganate (strong oxidizing agent), a violent redox reaction accompanied by self-ignition starts. Redox (reduction–oxidation, pronunciation: or ) is a type of chemical reaction in whi ...

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 A permanganate is the general name for a chemical compound containing the manganate(VII) ion, (). Because manganese is in the +7 oxidation state, the permanganate(VII) ion is a strong oxidizing agent. The ion has tetrahedral geometry. Permanganate ...
often converts a methyl group to a carboxyl (–COOH) group, e.g. the conversion of
toluene Toluene (), also known as toluol (), is an aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH₃) attached to ...
to
benzoic acid Benzoic acid is a white (or colorless) solid with the formula C6H5CO2H. It is the simplest aromatic carboxylic acid. The name is derived from gum benzoin, which was for a long time its only source. Benzoic acid occurs naturally in many plants a ...
. Ultimately oxidation of methyl groups gives
proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Protons and neutrons, each with masses of approximately one atomic mass unit, are collecti ...
s and
carbon dioxide Carbon dioxide (chemical formula ) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules consist of a carbon atom covalently double bonded to two oxygen atoms. It occurs naturally in Earth's atmospher ...

carbon dioxide
, as seen in combustion.


Methylation

Demethylation (the transfer of the methyl group to another compound) is a common process, and
reagent 200px, Reactants, such as sulfur (''pictured''), are the starting materials that are used in chemical reactions. A reagent is a substance or compound added to a system to cause a chemical reaction, or added to test if a reaction occurs. The terms ...
s that undergo this reaction are called methylating agents. Common methylating agents are
dimethyl sulfate Dimethyl sulfate is a chemical compound with formula (CH3O)2SO2. As the diester of methanol and sulfuric acid, its formula is often written as (CH3)2SO4 or Me2SO4, where CH3 or Me is methyl. Me2SO4 is mainly used as a methylating agent in organi ...
,
methyl iodide Iodomethane, also called methyl iodide, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one hyd ...
, and
methyl triflate Methyl trifluoromethanesulfonate, also commonly called methyl triflate and abbreviated MeOTf, is the organic compound with the formula CF3SO2OCH3. It is a colourless liquid which finds use in organic chemistry as a powerful methylating agent. The ...
.
Methanogenesis Methanogenesis or biomethanation is the formation of methane by microbes known as methanogens. Organisms capable of producing methane have been identified only from the domain Archaea, a group phylogenetically distinct from both eukaryotes and bact ...
, the source of natural gas, arises via a demethylation reaction. Together with ubiquitin and phosphorylation, methylation is a major biochemical process for modifying protein function.


Deprotonation

Certain methyl groups can be deprotonated. For example, the acidity of the methyl groups in
acetone Acetone, or propanone, is an organic compound with the formula (CH3)2CO. It is the simplest and smallest ketone. It is a colourless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscible with water and se ...
((CH3)2CO) is about 1020 times more acidic than methane. The resulting
carbanionA carbanion is an anion in which carbon is trivalent (forms three bonds) and bears a formal negative charge (in at least one significant resonance form). Formally, a carbanion is the conjugate base of a carbon acid: :R3CH + :B− → R3C:− + HB ...
s are key intermediates in many reactions in
organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one of t ...
and
biosynthesisBiosynthesis is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined together to form macromole ...

biosynthesis
.
Fatty acid fatty acids have perfectly straight chain structure. Unsaturated ones are typically bent, unless they have a trans configuration. In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with a long aliphatic chain, which is ...
s are produced in this way.


Free radical reactions

When placed in
benzylic In organic chemistry, benzyl is the substituent or molecular fragment possessing the structure C6H5CH2–. Benzyl features a benzene ring attached to a CH2 group. Nomenclature In IUPAC nomenclature the prefix benzyl refers to a C6H5CH2 substituent ...
or
allylic An allyl group is a substituent with the structural formula H2C=CH−CH2R, where R is the rest of the molecule. It consists of a methylene bridge (−CH2−) attached to a vinyl group (−CH=CH2). The name is derived from the Latin word for garlic, ...
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 Photochemistry is the branch of chemistry concerned with the chemical effects of light. Generally, this term is used to describe a chemical reaction caused by absorption of ultraviolet (wavelength from 100 to 400 nm), visible light (400–750 ...
chlorination
chlorination
of the methyl group in
toluene Toluene (), also known as toluol (), is an aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH₃) attached to ...
to give
benzyl chloride Benzyl chloride, or α-chlorotoluene, is an organic compound with the formula C6H5CH2Cl. This colorless liquid is a reactive organochlorine compound that is a widely used chemical building block. Preparation Benzyl chloride is prepared industrial ...
.M. Rossberg et al. “Chlorinated Hydrocarbons” in Ullmann’s Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim.


Chiral methyl

In the special case where one hydrogen is replaced by
deuterium Deuterium (or hydrogen-2, symbol or , also known as heavy hydrogen) is one of two stable isotopes of hydrogen (the other being protium, or hydrogen-1). The nucleus of a deuterium atom, called a deuteron, contains one proton and one neutron, wher ...
(D) and another hydrogen by
tritium Tritium ( or ) or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen. The nucleus of tritium (sometimes called a triton) contains one proton and two neutrons, whereas the nucleus of the common isotope hydrogen-1 (''protium' ...
(T), the methyl substituent becomes
chiral that is chiral Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand," a familiar chiral object. An object or a system is ''chiral'' if it is distingui ...
. Methods exist to produce optically pure methyl compounds, e.g., chiral
acetic acid Acetic acid , systematically named ethanoic acid , is a colourless liquid organic compound with the chemical formula CH3COOH (also written as CH3CO2H, C2H4O2, or HC2H3O2). Vinegar is no less than 4% acetic acid by volume, making acetic acid ...

acetic acid
(CHDTCO2H). Through the use of chiral methyl groups, the
stereochemicals. Stereochemistry focuses on stereoisomers Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focu ...
course of several
biochemical Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and ...
transformations have been analyzed.


Rotation

A methyl group may rotate around the R—C axis. This is a free rotation only in the simplest cases like gaseous CClH3. In most molecules, the remainder R breaks the ''C'' symmetry of the R—C axis and creates a potential ''V''(''φ'') that restricts the free motion of the three protons. For the model case of C2H6 this is discussed under the name ethane barrier. In condensed phases, neighbour molecules also contribute to the potential. Methyl group rotation can be experimentally studied using quasielastic neutron scattering.


Etymology

French chemists
Jean-Baptiste Dumas Jean Baptiste André Dumas (14 July 180010 April 1884) was a French chemist, best known for his works on organic analysis and synthesis, as well as the determination of atomic weights (relative atomic masses) and molecular weights by measuring va ...
and
Eugene Peligot Eugene may refer to: People * Eugene (given name), information about the name including a list of people with the given name * Eugene (actress) (born 1981), South Korean actress and former member of singing group S.E.S. * Eugene (wrestler) prof ...
, after determining methanol's chemical structure, introduced "methylene" from the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of ...
''methy'' "wine" and ''hȳlē'' "wood, patch of trees" with the intention of highlighting its origins, "alcohol made from wood (substance)".Note that the correct Greek word for the substance "wood" is ''xylo-''. The term "methyl" was derived in about 1840 by
back-formation In etymology, back-formation is the process of creating a new lexeme by removing actual or supposed affixes.Crystal, David. ''A Dictionary of Linguistics and Phonetics, Sixth Edition'', Blackwell Publishers, 2008. The resulting neologism is called ...
from "methylene", and was then applied to describe "methyl alcohol" (which since 1892 is called "
methanol Methanol, also known as methyl alcohol amongst other names, is a chemical and the simplest alcohol, with the formula CH3OH (a methyl group linked to a hydroxyl group, often abbreviated MeOH). It is a light, volatile, colourless, flammable liquid ...
"). ''Methyl'' is the
IUPAC nomenclature of organic chemistry In chemical nomenclature, the IUPAC nomenclature of organic chemistry is a method of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC). It is published in the ''Nomenclature of Organi ...
term for an
alkane , the simplest alkane In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree st ...
(or alkyl) molecule, using the prefix "meth-" to indicate the presence of a single carbon.


References

{{DEFAULTSORT:Methyl Group Alkyl groups Functional groups