Editing Methyl radical

{{Chembox
| Watchedfields = changed
| ImageFile = Radical metilo--methyl radical.svg
| ImageFile_Ref = {{Chemboximage|correct|??}}
| ImageSize = 121
| IUPACName = Methyl<ref>{{cite book |author=[[International Union of Pure and Applied Chemistry]] |date=2014 |title=Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 |publisher=[[Royal Society of Chemistry|The Royal Society of Chemistry]] |pages=1051 |doi=10.1039/9781849733069 |isbn=978-0-85404-182-4}}</ref>
|Section1={{Chembox Identifiers
| CASNo = 2229-07-4
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = S19006ZD7R 
| CASNo_Ref = {{cascite|correct|??}}
| PubChem = 3034819
| ChemSpiderID = 2299212
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| MeSHName = Methyl+radical
| ChEBI = 29309
| Beilstein = 1696831
| Gmelin = 57
| SMILES = [CH3]
| StdInChI = 1S/CH3/h1H3
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = WCYWZMWISLQXQU-UHFFFAOYSA-N
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}}}
|Section2={{Chembox Properties
| C=1 | H=3 
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}}

'''Methyl radical''' is an [[organic compound]] with the [[chemical formula]] {{Chem|CH|3|•}} (also written as {{Chem|[CH|3|]}}<sup>•</sup>). It is a metastable colourless gas, which is mainly produced ''in situ'' as a precursor to other hydrocarbons in the petroleum cracking industry. It can act as either a strong [[oxidant]] or a strong [[reductant]], and is quite corrosive to metals.

== Chemical properties ==
Its first ionization potential (yielding the [[methenium]] ion, {{chem|CH|3|+}}) is {{val|9.837|0.005|ul=eV}}.<ref name=Golob> {{cite journal | last1 = Golob | first1 = L. | last2 = Jonathan | first2 = N. | last3 = Morris | first3 = A. | last4 = Okuda | first4 = M. | last5 = Ross | first5 = K.J. | year = 1972 | title = The first ionization potential of the methyl radical as determined by photoelectron spectroscopy | journal = Journal of Electron Spectroscopy and Related Phenomena | volume = 1 | issue = 5| pages = 506–508 | doi = 10.1016/0368-2048(72)80022-7 | bibcode = 1972JESRP...1..506G }}</ref>

=== Redox behaviour ===
The carbon centre in methyl can bond with electron-donating molecules by reacting:
:{{Chem|CH|3|•}} + R<sup>•</sup> → {{Chem|RCH|3}}
Because of the capture of the nucleophile (R<sup>•</sup>), methyl has oxidising character. Methyl is a strong oxidant with organic chemicals. However, it is equally a strong reductant with chemicals such as water. It does not form aqueous solutions, as it reduces water to produce [[methanol]] and elemental hydrogen:
:2&nbsp;{{Chem|CH|3|•}} + 2&nbsp;{{Chem|H|2|O}} → 2&nbsp;{{Chem|CH|3|OH}} + {{Chem|H|2}}

=== Structure ===
The [[molecular geometry]] of the methyl radical is [[trigonal planar molecular geometry|trigonal planar]] (bond angles are 120°), although the energy cost of distortion to a [[trigonal pyramidal molecular geometry|pyramidal geometry]] is small.  All other electron-neutral, non-conjugated alkyl radicals are pyramidalized to some extent, though with very small inversion barriers.  For instance, the [[t-Butyl|''t''-butyl]] radical has a bond angle of 118° with a {{cvt|0.7|kcal/mol|kJ/mol}} barrier to [[pyramidal inversion]]. On the other hand, substitution of hydrogen atoms by more electronegative substituents leads to radicals with a strongly pyramidal geometry (112°), such as the  [[trifluoromethyl]] radical, {{chem|CF|3|•}}, with a much more substantial inversion barrier of around {{cvt|25|kcal/mol|kJ/mol}}.<ref>Anslyn E.V. and Dougherty D.A., ''Modern Physical Organic Chemistry'' (University Science Books, 2006), p.57</ref>

=== Chemical reactions ===
Methyl undergoes the typical chemical reactions of a radical. Below approximately {{Convert|1100|C|K|-2}}, it rapidly dimerises to form [[ethane]]. Upon treatment with an alcohol, it converts to [[methane]] and either an alkoxy or hydroxyalkyl. Reduction of methyl gives methane. When heated above, at most, {{Convert|1400|C|K|-2}}, methyl decomposes to produce [[methylidyne]] and elemental hydrogen, or to produce [[methylene radical|methylene]] and atomic hydrogen:
:{{Chem|CH|3|•}} → CH<sup>•</sup> + {{Chem|H|2}}
:{{Chem|CH|3|•}} → {{Chem|CH|2|•}} + H<sup>•</sup>
Methyl is very corrosive to metals, forming methylated metal compounds:
:M + ''n''&nbsp;{{Chem|CH|3|•}} → M(CH<sub>3</sub>)<sub>''n''</sub>

== Production ==
===Biosynthesis===
Some [[radical SAM]] enzymes generate methyl radicals by reduction of S-adenosylmethionine.<ref>{{cite journal|author1=Ribbe, M. W. |author2=Hu, Y. |author3=Hodgson, K. O. |author4=Hedman, B. |title=Biosynthesis of Nitrogenase Metalloclusters|journal=Chemical Reviews|year=2014|volume=114|issue=8|pages=4063–4080|doi=10.1021/cr400463x|pmc=3999185|pmid=24328215}}</ref>

=== Acetone photolysis ===
It can be produced by the ultraviolet photodissociation of [[acetone]] vapour at 193&nbsp;nm:<ref name=Hall1991>{{cite journal|last1=Hall|first1=G. E.|last2=Vanden Bout|first2=D.|last3=Sears|first3=Trevor J.|title=Photodissociation of acetone at 193 nm: Rotational- and vibrational-state distributions of methyl fragments by diode laser absorption/gain spectroscopy|journal=The Journal of Chemical Physics|date=1991|volume=94|issue=6|page=4182|doi=10.1063/1.460741|publisher=[[AIP Publishing]]|bibcode = 1991JChPh..94.4182H |url=https://zenodo.org/record/1232934}}</ref>
:{{Chem|C|3|H|6|O}} → CO + 2&nbsp;{{Chem|CH|3|•}}

=== Halomethane photolysis ===
It is also produced by the ultraviolet dissociation of [[halomethane]]s:
:{{Chem|CH|3|X}} → X<sup>•</sup> + {{Chem|CH|3|•}}

=== Methane oxidation ===
{{Details|Atmospheric methane#Removal processes}}
It can also be produced by the reaction of [[methane]] with the [[hydroxyl radical]]: 
:OH<sup>•</sup> + CH<sub>4</sub> → {{Chem|CH|3|•}} + H<sub>2</sub>O
This process begins the major removal mechanism of methane from the atmosphere.  The reaction occurs in the [[troposphere]] or [[stratosphere]]. In addition to being the largest known sink for atmospheric methane, this reaction is one of the most important sources of water vapor in the upper atmosphere.

This reaction in the [[troposphere]] gives a methane lifetime of 9.6 years. Two more minor sinks are soil sinks (160 year lifetime) and stratospheric loss by reaction with <sup>•</sup>OH, <sup>•</sup>Cl and <sup>•</sup>O<sup>1</sup>D in the stratosphere (120 year lifetime), giving a net lifetime of 8.4 years.<ref name="Trace Gases">{{cite web
| url=http://www.grida.no/climate/ipcc_tar/wg1/134.htm#4211
| title=Trace Gases: Current Observations, Trends, and Budgets
| work=Climate Change 2001, IPCC Third Assessment Report
| publisher=IPCC/United Nations Environment Programme}}</ref>

=== Azomethane pyrolysis ===
Methyl radicals can also be obtained by [[pyrolysis]] of [[Azo compound#Alkyl azo compounds|azomethane]], CH<sub>3</sub>N=NCH<sub>3</sub>, in a low-pressure system.

== In the interstellar medium ==

Methyl was discovered in [[interstellar medium]] in 2000 by a team led by Helmut Feuchtgruber who detected it using the [[Infrared Space Observatory]]. It was first detected in molecular clouds toward the centre of the Milky Way.<ref name=ESA2000>{{cite web|title=ISO detects a new molecule in interstellar space|url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=21831|work=Science & Technology|publisher=[[European Space Agency]]|access-date=17 June 2013}}</ref>

== References ==
{{Reflist}}
{{Molecules detected in outer space}}
{{Hydrides by group}}

[[Category:Astrochemistry]]
[[Category:Free radicals]]
[[Category:Oil refining]]
[[Category:Methane|Yl]]