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In organic chemistry, a methoxy group is the functional group consisting of a methyl group bound to oxygen. This alkoxy group has the formula R−O−CH₃.

On a benzene ring, the Hammett equation classifies a methoxy substituent at the para position as an electron-donating group, but as an electron-withdrawing group if at the meta position. At the ortho position, steric effects 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 and dimethyl ether. Other methoxy ethers include anisole and vanillin. Many metal alkoxides contain methoxy groups, such as tetramethyl orthosilicate and titanium methoxide. 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, 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-methyltransferases that act on phenols, such as catechol-O-methyl transferase (COMT). Many natural products in plants, such as 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 phenols, or by methoxylation of aryl halides.

References

1. Streitwieser, Andrew (1992). Introduction to organic chemistry. Heathcock, Clayton H., Kosower, Edward M. (4th ed.). New York: Macmillan. pp. 515. ISBN 0024181706. OCLC 24501305.
2. Boerjan, Wout; Ralph, John; Baucher, Marie (2003). "Lignin Biosynthesis". Annu. Rev. Plant Biol. 54 (1): 519–46. doi:10.1146/annurev.arplant.54.031902.134938. PMID 14503002.
3. Scarrow, J. A.; Allen, C. F. H. (1933). "Methoxyacetonitrile". Org. Synth. 13: 56. doi:10.15227/orgsyn.013.0056.
4. Cornella, Josep; Zarate, Cayetana; Martin, Ruben (2014). "Ni-catalyzed Reductive Cleavage of Methyl 3-Methoxy-2-Naphthoate". Org. Synth. 91: 260–272. doi:10.15227/orgsyn.091.0260.
5. Cheung, Chi Wai; Buchwald, Stephen L. (2 August 2013). "Mild and General Palladium-Catalyzed Synthesis of Methyl Aryl Ethers Enabled by the Use of a Palladacycle Precatalyst". Organic Letters. 15 (15): 3998–4001. doi:10.1021/ol401796v. PMC 3776604. PMID 23883393.
6. Tolnai, Gergely L.; Pethő, Bálint; Králl, Péter; Novák, Zoltán (13 January 2014). "Palladium-Catalyzed Methoxylation of Aromatic Chlorides with Borate Salts". Advanced Synthesis & Catalysis. 356 (1): 125–129. doi:10.1002/adsc.201300687.

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Molecules	Diatomic Aluminium monochloride Aluminium monofluoride Aluminium(II) oxide Argonium Carbon cation Carbon monophosphide Carbon monosulfide Carbon monoxide Cyano radical Diatomic carbon Fluoromethylidynium Helium hydride ion Hydrogen chloride Hydrogen fluoride Hydrogen (molecular) Hydroxyl radical Iron(II) oxide Magnesium monohydride Methylidyne radical Nitric oxide Nitrogen (molecular) Imidogen Sulfur mononitride Oxygen (molecular) Phosphorus monoxide Phosphorus mononitride Potassium chloride Silicon carbide Silicon monoxide Silicon monosulfide Sodium chloride Sodium iodide Sulfanyl Sulfur monoxide Titanium(II) oxide Triatomic Aluminium(I) hydroxide Aluminium isocyanide Amino radical Carbon dioxide Carbonyl sulfide CCP radical Chloronium Diazenylium Dicarbon monoxide Disilicon carbide Ethynyl radical Formyl radical Hydrogen cyanide (HCN) Hydrogen isocyanide (HNC) Hydrogen sulfide Hydroperoxyl Iron cyanide Isoformyl Magnesium cyanide Magnesium isocyanide Methylene N2H Nitrous oxide Nitroxyl Ozone Methylidynephosphane Potassium cyanide Trihydrogen cation Sodium cyanide Sodium hydroxide Silicon carbonitride c-Silicon dicarbide SiNC Sulfur dioxide Thioformyl Thioxoethenylidene Titanium dioxide Tricarbon Water Four atoms Acetylene Ammonia Isocyanic acid Cyanoethynyl Formaldehyde Fulminic acid HCCN Hydrogen peroxide Hydromagnesium isocyanide Isocyanic acid Isothiocyanic acid Ketenyl Methylene amidogen Methyl cation Methyl radical Propynylidyne Protonated carbon dioxide Protonated hydrogen cyanide Silicon tricarbide Thioformaldehyde Tricarbon monoxide Tricarbon monosulfide Thiocyanic acid Five atoms Ammonium ion Butadiynyl Carbodiimide Cyanamide Cyanoacetylene Cyanoformaldehyde Cyanomethyl Cyclopropenylidene Formic acid Isocyanoacetylene Ketene Methane Methoxy radical Methylenimine Propadienylidene Protonated formaldehyde Silane Silicon-carbide cluster Six atoms Acetonitrile Cyanobutadiynyl radical E-Cyanomethanimine Cyclopropenone Diacetylene Ethylene Formamide HC4N Ketenimine Methanethiol Methanol Methyl isocyanide Pentynylidyne Propynal Protonated cyanoacetylene Seven atoms Acetaldehyde Acrylonitrile Vinyl cyanide Cyanodiacetylene Ethylene oxide Glycolonitrile Hexatriynyl radical Propyne Methylamine Methyl isocyanate Vinyl alcohol Eight atoms Acetic acid Aminoacetonitrile Cyanoallene Ethanimine Glycolaldehyde Hexapentaenylidene Methylcyanoacetylene Methyl formate Acrolein Nine atoms Acetamide Cyanohexatriyne Dimethyl ether Ethanol Methyldiacetylene Octatetraynyl radical Propene Ethanethiol Propionitrile N-Methylformamide Ten atoms or more Acetone Benzene Benzonitrile Buckminsterfullerene (C60, C60, fullerene, buckyball) C70 fullerene Cyanodecapentayne Ethylene glycol Ethyl formate Methyl acetate Methyl-cyano-diacetylene Methyltriacetylene Propionaldehyde Butyronitrile Pyrimidine Heptatrienyl radical
Deuterated molecules	Ammonia Ammonium ion Formaldehyde Formyl radical Heavy water Hydrogen cyanide Hydrogen deuteride Hydrogen isocyanide Propyne N2D Trihydrogen cation
Unconfirmed	Anthracene Dihydroxyacetone Methoxyethane Glycine Graphene Hemolithin H2NCO Linear C5 Naphthalene cation Phosphine Pyrene Silylidyne
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• O-methylation
• Alkoxy groups
• Methoxy compounds