In organic chemistry, a methoxy group is the functional group consisting of a methyl group bound to oxygen. This alkoxy group has the formula . On a benzene ring, the Hammett equation classifies a methoxy substituent at the ''para'' position as an

electron-donating group In chemistry, electron-rich is jargon that is used in multiple related meanings with either or both kinetic and thermodynamic implications: *with regards to electron-transfer, electron-rich species have low ionization energy and/or are reducing a ...

, 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 and vanillin. Many alkoxides contain methoxy groups, e.g. tetramethyl orthosilicate and titanium methoxide. Such compounds are often classified as methoxides. Esters with a methoxy group can be referred to as methyl esters, and the —COOCH₃ 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 flavonoids, 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 phenols, e.g., catechol-O-methyl transferase (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 phenols, or by methoxylation of aryl halides.

References

{{Molecules detected in outer space Alkoxy groups