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 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 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 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 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 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. lignins, are generated via catalysis by caffeoyl-CoA O-methyltransferase.

Methoxylation

Organic methoxides are often produced by methylation 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