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A '''radical ion''' is a [[Radical (chemistry)|free radical]] species that carries a [[charge (chemistry)|charge]].<ref>{{GoldBookRef|title=radical ion|file= R05073}}</ref> Radical [[ion]]s are encountered in [[organic chemistry]] as [[reactive intermediates]] and in [[mass spectrometry]] as gas phase ions. Positive radical ions are called radical cations whereas negative radical ions are called radical anions.
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==Notation==
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In organic chemistry, a radical ion is typically indicated by a superscript dot followed by the sign of the charge: <math>M^{\bullet +}</math> and <math>M^{\bullet -}</math>. In mass spectrometry, the sign is written first, followed by the superscripted dot: <math>M^{+\bullet}</math> and <math>M^{-\bullet}</math>.<ref name="isbn0-9660813-2-3">{{cite book |author=Sparkman, O. David |title=Mass spectrometry desk reference |publisher=Global View Pub |location=Pittsburgh |year=2000 |isbn=0-9660813-2-3 |oclc= |doi= |page=53}}</ref>
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== Radical anions ==
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Many [[aromatic]] compounds can undergo [[one-electron reduction]] by [[alkali metal]]s. For example the reaction of [[naphthalene]] with [[sodium]] in an aprotic solvent yields the naphthalene '''radical anion''' - sodium ion salt. In a [[ESR spectrum]] this compound shows up as a [[quintet]] of quintets (25 lines). In the presence of a [[hydrogen ion|proton]] source the radical anion is protonated and effectively hydrogenated like in the [[Birch reduction]].


The electron is transferred from the alkali metal ion to an unoccupied antibonding p-p п* orbital of the aromatic molecule.  This transfer is usually only energetically favorable if the aprotic solvent efficiently solvates the alkali metal ion.  Effectiveness for this is in the order [[diethyl ether]] < THF < [[dimethoxyethane|1,2-dimethoxyethane]] < [[HMPA]].  In principle any unsaturated molecule can form a radical anion, but the antibonding orbitals are only energetically accessible in more extensive conjugated systems.  Ease of formation is in the order [[benzene]] < [[naphthalene]] < [[anthracene]] < [[pyrene]], etc.  On addition of a proton source, the structure of the resulting hydrogenated molecule is defined by the charge distribution of the radical anion.  For instance, the anthracene radical anion forms mainly (but not exclusively) 9,10-dihydroanthracene.
'''MathML'''
:<math forcemathmode="mathml">E=mc^2</math>


An example of a non-carbon radical anion is the [[superoxide]] anion, formed by transfer of one electron to an [[oxygen]] molecule.
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A very effective way to remove any traces of water from [[THF]] is by [[reflux]] with [[sodium]] wire in the presence of a small amount of [[benzophenone]]. Benzophenone is reduced to the [[ketyl]] radical anion by sodium which gives the THF solution an intense blue color. However, any trace of water in THF will further reduce the ketyl to the colourless [[alcohol]]. In this way, the color of the THF signals the dryness and the [[distilled]] THF contains less than 10 [[Parts per million|ppm]] of water.<ref>[http://www.erowid.org/archive/rhodium/chemistry/equipment/benzophenone.ketyl.html The Benzophenone Ketyl Still Pot - [www.rhodium.ws&#93;<!-- Bot generated title -->]</ref> This treatment also effectively removes any peroxides in the THF.  Radical anions of this type are also involved in the [[Acyloin condensation]].
'''source'''
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[[Cyclooctatetraene]] is reduced by elemental [[potassium]] all the way to the dianion because the 10 electron system is aromatic. [[Quinone]] is reduced to a [[semiquinone]] radical anion. [[Semidione]]s are derived from the reduction of dicarbonyl compounds.
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== Radical cations ==
==Demos==
Cationic radical species do also exist but are much less stable. They appear prominently in mass spectrometry, and some compounds containing the [[dioxygenyl]] cation can be prepared in bulk.<ref>{{cite doi|10.1021/ic50013a036}}</ref> When a gas-phase molecule is subjected to [[electron ionization]] one electron is abstracted by an electron in the electron beam to create a radical cation M<sup>+</sup><sup>.</sup>. This species represents the [[molecular ion]] or parent ion and will tell the precise [[molecular weight]]. On a typical [[mass spectrum]] more signals show up because the molecular ion fragments into a complex mixture of ions and uncharged radical species. For example the [[methanol]] radical cation fragments into a [[methyl]] cation CH<sub>3</sub><sup>+</sup> and a [[hydroxyl]] radical. In [[naphthalene]] the unfragmented radical cation is by far the most prominent peak in the mass spectrum. Secondary species are generated from [[hydrogen ion|proton]] gain (M+1) and proton loss (M-1).


[[Polaron]]s and [[bipolaron]]s are radical cations encountered in doped [[conducting polymer]]s.
Here are some [https://commons.wikimedia.org/w/index.php?title=Special:ListFiles/Frederic.wang demos]:


==References==
{{Reflist}}


{{DEFAULTSORT:Radical Ion}}
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[[Category:Reactive intermediates]]
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[[Category:Mass spectrometry]]
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[[fr:Ion radicalaire]]
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[[it:Ione radicalico]]
 
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==Bug reporting==
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Latest revision as of 23:52, 15 September 2019

This is a preview for the new MathML rendering mode (with SVG fallback), which is availble in production for registered users.

If you would like use the MathML rendering mode, you need a wikipedia user account that can be registered here [[1]]

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