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 r ...

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 ma ...

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 ...

. This alkoxy group has the formula . On a benzene ring, 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 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 ...

, 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 ...

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 i ...

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 u ...

. Many alkoxides contain methoxy groups, e.g. tetramethyl orthosilicate and titanium methoxide. Such compounds are often classified as methoxides.

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 ...

s 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 a ...

, 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 sp ...

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 O-m ...

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 r ...

s, 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 a ...

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 ...

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 ...

of alkoxides. Some aryl methoxides can be synthesized by metal-catalyzed methylation of

s, or by methoxylation of aryl halides.

References

{{Molecules detected in outer space Alkoxy groups