![Methoxy group](https://upload.wikimedia.org/wikipedia/commons/4/43/Methoxy_group.svg)
In
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; ...
, a methoxy group is the
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest ...
consisting of a
methyl group
In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in many ...
bound to
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
. This
alkoxy group
In chemistry, the alkoxy group is an alkyl group which is singularly bonded to oxygen; thus . The range of alkoxy groups is vast, the simplest being methoxy (). An ethoxy group () is found in the organic compound ethyl phenyl ether (, also k ...
has the formula .
On a
benzene ring
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...
, the
Hammett equation
The Hammett equation in organic chemistry describes a linear free-energy relationship relating reaction rates and equilibrium constants for many reactions involving benzoic acid derivatives with meta- and para-substituents to each other with ju ...
classifies a methoxy substituent at the ''para'' position as an
electron-donating group, but as an
electron-withdrawing group
In chemistry, an electron-withdrawing group (EWG) is a substituent that has some of the following kinetic and thermodynamic implications:
*with regards to electron transfer, electron-withdrawing groups enhance the oxidizing power tendency of the ...
if at the ''meta'' position. At the ''ortho'' position,
steric effects
Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape ( conformation) and reactivity of ions ...
are likely to cause a significant alteration in the Hammett equation prediction which otherwise follows the same trend as that of the ''para'' position.
Occurrence
The simplest of methoxy compounds are
methanol
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...
and
dimethyl ether
Dimethyl ether (DME; also known as methoxymethane) is the organic compound with the formula CH3OCH3,
(sometimes ambiguously simplified to C2H6O as it is an isomer of ethanol). The simplest ether, it is a colorless gas that is a useful precursor ...
. Other methoxy ethers include
anisole
Anisole, or methoxybenzene, is an organic compound with the formula CH3OC6H5. It is a colorless liquid with a smell reminiscent of anise seed, and in fact many of its derivatives are found in natural and artificial fragrances. The compound is ...
and
vanillin
Vanillin is an organic compound with the molecular formula . It is a phenolic aldehyde. Its functional groups include aldehyde, hydroxyl, and ether. It is the primary component of the extract of the vanilla bean. Synthetic vanillin is now used ...
. Many alkoxides contain methoxy groups, e.g.
tetramethyl orthosilicate
Tetramethyl orthosilicate (TMOS) is the chemical compound with the formula Si(OCH3)4. This molecule consists of four methoxy groups bonded to a silicon atom. The basic properties are similar to the more popular tetraethyl orthosilicate, which i ...
and
titanium methoxide
Titanium ethoxide is a chemical compound with the formula Ti4(OCH2CH3)16. It is a colorless liquid that is soluble in organic solvents but hydrolyzes readily. It is sold commercially as a colorless solution. Alkoxides of titanium(IV) and zirconium ...
. Such compounds are often classified as
methoxide
In organic chemistry, methoxides are organic salts with a anion. They are the simplest alkoxides. Sodium methoxide and potassium methoxide have widespread use, though other metal-cation variants such as lithium methoxide, rubidium methoxide, ...
s.
Ester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...
s with a methoxy group can be referred to as methyl esters, and the —COOCH
3 substituent is called a methoxycarbonyl.
Biosynthesis
In nature, methoxy groups are found on nucleosides that have been subjected to
2'-O-methylation
2'-''O''-methylation is a common nucleoside modification of RNA, where a methyl group is added to the 2' hydroxyl of the ribose moiety of a nucleoside, producing a methoxy group. 2'-''O''-methylated nucleosides are mostly found in ribosomal RNA ...
, for example in variations of the
5'-cap structure known as cap-1 and cap-2. They are also common substituents in
O-methylated flavonoid The O-methylated flavonoids or methoxyflavonoids are flavonoids with methylations on hydroxyl groups (methoxy bonds). O-methylation has an effect on the solubility of flavonoids.
Enzymes
O-methylated flavonoids formation implies the presence of spe ...
s, whose formation is catalyzed by
O-methyltransferase An O-methyltransferase (OMT) is a type of methyltransferase enzyme transferring a methyl group on a molecule.
Examples are :
* Acetylserotonin O-methyltransferase
* Apigenin 4'-O-methyltransferase
* Caffeate O-methyltransferase
* Caffeoyl-CoA ...
s that act on
phenol
Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it req ...
s, e.g.,
catechol-O-methyl transferase
Catechol-''O''-methyltransferase (COMT; ) is one of several enzymes that degrade catecholamines (neurotransmitters such as dopamine, epinephrine, and norepinephrine), catecholestrogens, and various drugs and substances having a catechol structu ...
(COMT). Many natural products in plants, e.g.
lignin
Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...
s, are generated via catalysis by
caffeoyl-CoA O-methyltransferase
In enzymology, a caffeoyl-CoA O-methyltransferase () is an enzyme that catalyzes the chemical reaction
:S-adenosyl-L-methionine + caffeoyl-CoA \rightleftharpoons S-adenosyl-L-homocysteine + feruloyl-CoA
Thus, the two substrates of this enzyme a ...
.
Methoxylation
Organic methoxides are often produced by
methylation
In the chemical sciences, methylation denotes the addition of a methyl group on a substrate, or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation, with a methyl group replacing a hydrogen atom. These t ...
of alkoxides. Some aryl methoxides can be synthesized by metal-catalyzed methylation of
phenol
Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it req ...
s, or by methoxylation of
aryl halide In organic chemistry, an aryl halide (also known as haloarene) is an aromatic compound in which one or more hydrogen atoms, directly bonded to an aromatic ring are replaced by a halide. The haloarene are different from haloalkanes because they exh ...
s.
References
{{Molecules detected in outer space
Alkoxy groups