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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.
| | Emilia Shryock is my name but you can call me something you like. The preferred pastime for my children and me is to play baseball and I'm attempting to make it a profession. Years in the past we moved to North Dakota. Since she was eighteen she's been operating as a receptionist but her promotion by no means comes.<br><br>my weblog: [http://huiyuan.fancai.com/space.php?uid=85084&do=blog&id=473364 huiyuan.fancai.com] |
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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 an [[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]].
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| 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]] < [[tetrahydrofurane|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. | |
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| 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]<!-- 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]].
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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 ==
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| Cationic radical species are much less stable. They appear prominently in the mass spectrometry. 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. A typical [[mass spectrum]] shows multiple signals because the molecular ion fragments into a complex mixture of ions and uncharged radical species. For example the [[methanol]] radical cation fragments into a [[methenium]] 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).
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| Some compounds containing the [[dioxygenyl]] cation can be prepared in bulk.<ref>{{cite doi|10.1021/ic50013a036}}</ref>
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| ===Organic conductors===
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| Radical cations figure prominently in the chemistry and properties of [[conducting polymer]]s. Such polymers are formed by the oxidation of [[heterocycle]]s to give radical cations, which condense with the parent heterocycle. For example, [[polypyrrole]] is prepared by oxidation of [[pyrrole]] using [[ferric chloride]] in methanol:
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| :n C<sub>4</sub>H<sub>4</sub>NH + 2 FeCl<sub>3</sub> → (C<sub>4</sub>H<sub>2</sub>NH)<sub>n</sub> + 2 FeCl<sub>2</sub> + 2 HCl
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| Once formed, these polymers become conductive upon oxidation.<ref name=RussChemRev>"Polypyrrole: a conducting polymer; its synthesis, properties and applications" Russ. Chem. Rev. 1997, vol. 66, p.443ff.(http://iopscience.iop.org/0036-021X/66/5/R04)</ref> [[Polaron]]s and [[bipolaron]]s are radical cations encountered in doped [[conducting polymer]]s.
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| ==References== | |
| {{Reflist}}
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| {{DEFAULTSORT:Radical Ion}}
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| [[Category:Reactive intermediates]]
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| [[Category:Mass spectrometry]]
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Emilia Shryock is my name but you can call me something you like. The preferred pastime for my children and me is to play baseball and I'm attempting to make it a profession. Years in the past we moved to North Dakota. Since she was eighteen she's been operating as a receptionist but her promotion by no means comes.
my weblog: huiyuan.fancai.com