{"history":[],"article":{"id":"0ec3e013-36f9-4ab6-b8f8-66f6da5770b7","title":"Radical anion","slug":"radical-anion","content":":::summary\n:::\n\n# \nIn [organic chemistry](https://bliptext.com/articles/organic-chemistry), a **radical anion** is a [free radical](https://bliptext.com/articles/radical-chemistry) species that carries a [negative charge](https://bliptext.com/articles/charge-chemistry).\nRadical [anions](https://bliptext.com/articles/anion) are encountered in [organic chemistry](https://bliptext.com/articles/organic-chemistry) as reduced derivatives of polycyclic aromatic compounds, e.g. [sodium naphthenide](https://bliptext.com/articles/sodium-naphthenide).\nAn example of a non-carbon radical anion is the [superoxide](https://bliptext.com/articles/superoxide) anion, formed by transfer of one electron to an [oxygen](https://bliptext.com/articles/oxygen) molecule.\nRadical anions are typically indicated by.\n# [Sodium naphthalene, a salt containing the radical anion of naphthalene as the anion | upload.wikimedia.org/wikipedia/commons/6/67/Sodium///naphthalenide.svg]\n\n# Polycyclic radical anions\nMany [aromatic](https://bliptext.com/articles/aromatic) compounds can undergo [one-electron reduction](https://bliptext.com/articles/one-electron-reduction) by [alkali metals](https://bliptext.com/articles/alkali-metal).\nThe electron is transferred from the alkali metal ion to an unoccupied antibonding p-p п* orbital of the aromatic molecule.\nThis transfer is usually only energetically favorable if the aprotic solvent efficiently solvates the alkali metal ion.\nEffective solvents are those that bind to the alkali metal cation: [diethyl ether](https://bliptext.com/articles/diethyl-ether) < [THF](https://bliptext.com/articles/tetrahydrofurane) < [1,2-dimethoxyethane](https://bliptext.com/articles/dimethoxyethane) < [HMPA](https://bliptext.com/articles/hmpa).\nIn principle any unsaturated molecule can form a radical anion, but the antibonding orbitals are only energetically accessible in more extensive conjugated systems.\nEase of formation is in the order [benzene](https://bliptext.com/articles/benzene) < [naphthalene](https://bliptext.com/articles/naphthalene) < [anthracene](https://bliptext.com/articles/anthracene) < [pyrene](https://bliptext.com/articles/pyrene), etc. Salts of the radical anions are often not isolated as solids but used in situ.\nThey are usually deeply colored.\n\n# Other examples\n[Cyclooctatetraene](https://bliptext.com/articles/cyclooctatetraene) is reduced by elemental [potassium](https://bliptext.com/articles/potassium) to the dianion.\nThe resulting dianion is a 10-pi electron system, which conforms to the [Huckel rule](https://bliptext.com/articles/huckel-rule) for [aromaticity](https://bliptext.com/articles/aromaticity).\n[Quinone](https://bliptext.com/articles/quinone) is reduced to a [semiquinone](https://bliptext.com/articles/semiquinone) radical anion.\n[Semidiones](https://bliptext.com/articles/semidione) are derived from the reduction of dicarbonyl compounds.\n\n# Reactions\n\n## Redox\nThe pi-radical anions are used as reducing agents in specialized syntheses.\nBeing soluble in at least some solvents, these salts act faster than the alkali metals themselves.\nThe disadvantages are that the polycyclic hydrocarbon must be removed.\nThe reduction potential of alkali metal naphthalene salts is about 3.1 V (vs Fc+/0).\nThe reduction potentials of the larger systems are lower, for example acenaphthalene is 2.45 V. Many radical anions are susceptible to further reduction to dianions.\n\n## Protonation\nAddition of a proton source (even water) to a radical anion results in protonation, i.e. the sequence of reduction followed by protonation is equivalent to [hydrogenation](https://bliptext.com/articles/hydrogenation).\nFor instance, the anthracene radical anion forms mainly (but not exclusively) 9,10-dihydroanthracene.\nRadical anions and their protonation are central to the [Birch reduction](https://bliptext.com/articles/birch-reduction).\n\n## Coordination to metal ions\nRadical anions of polycyclic aromatic compounds function as ligands in [organometallic chemistry](https://bliptext.com/articles/organometallic-chemistry).\n\n# Radical cations\nCationic radical species are much less common than the anions.\nDenoted, they appear prominently in mass spectrometry.\nWhen a gas-phase molecule is subjected to [electron ionization](https://bliptext.com/articles/electron-ionization) one electron is abstracted by an electron in the electron beam to create a radical cation M+..\nThis species represents the [molecular ion](https://bliptext.com/articles/molecular-ion) or parent ion.\nA typical [mass spectrum](https://bliptext.com/articles/mass-spectrum) shows multiple signals because the molecular ion fragments into a complex mixture of ions and uncharged radical species.\nFor example, the [methanol](https://bliptext.com/articles/methanol) radical cation fragments into a [methenium](https://bliptext.com/articles/methenium) cation CH3+ and a [hydroxyl](https://bliptext.com/articles/hydroxyl) radical.\nIn [naphthalene](https://bliptext.com/articles/naphthalene) the unfragmented radical cation is by far the most prominent peak in the mass spectrum.\nSecondary species are generated from [proton](https://bliptext.com/articles/hydrogen-ion) gain (M+1) and [proton](https://bliptext.com/articles/hydrogen-ion) loss (M-1).\nSome compounds containing the [dioxygenyl](https://bliptext.com/articles/dioxygenyl) cation can be prepared in bulk.\n\n## Organic conductors\nRadical cations figure prominently in the chemistry and properties of [conducting polymers](https://bliptext.com/articles/conducting-polymer).\nSuch polymers are formed by the oxidation of [heterocycles](https://bliptext.com/articles/heterocycle) to give radical cations, which condense with the parent heterocycle.\nFor example, [polypyrrole](https://bliptext.com/articles/poly[pyrrole](https://bliptext.com/articles/pyrrole)) is prepared by oxidation of [pyrrole](https://bliptext.com/articles/pyrrole) using [ferric chloride](https://bliptext.com/articles/ferric-chloride) in methanol:\nOnce formed, these polymers become conductive upon oxidation.\n[Polarons](https://bliptext.com/articles/polaron) and [bipolarons](https://bliptext.com/articles/bipolaron) are radical cations encountered in doped conducting polymers.","current_revision":null,"created_by":"kACnuQmH5k9Nr5VNVEpVeg7XpvUmMctD","created_at":"2025-01-25T21:40:17.857Z","updated_at":"2025-01-25T21:40:17.857Z","search_vector":"'anion':2 'radic':1","search_content":" \n \n\n# \nIn [organic chemistry](https://bliptext.com/articles/organic-chemistry), a **radical anion** is a [free radical](https://bliptext.com/articles/radical-chemistry) species that carries a [negative charge](https://bliptext.com/articles/charge-chemistry).\nRadical [anions](https://bliptext.com/articles/anion) are encountered in [organic chemistry](https://bliptext.com/articles/organic-chemistry) as reduced derivatives of polycyclic aromatic compounds, e.g. [sodium naphthenide](https://bliptext.com/articles/sodium-naphthenide).\nAn example of a non-carbon radical anion is the [superoxide](https://bliptext.com/articles/superoxide) anion, formed by transfer of one electron to an [oxygen](https://bliptext.com/articles/oxygen) molecule.\nRadical anions are typically indicated by.\n# [Sodium naphthalene, a salt containing the radical anion of naphthalene as the anion | upload.wikimedia.org/wikipedia/commons/6/67/Sodium///naphthalenide.svg]\n\n# Polycyclic radical anions\nMany [aromatic](https://bliptext.com/articles/aromatic) compounds can undergo [one-electron reduction](https://bliptext.com/articles/one-electron-reduction) by [alkali metals](https://bliptext.com/articles/alkali-metal).\nThe electron is transferred from the alkali metal ion to an unoccupied antibonding p-p п* orbital of the aromatic molecule.\nThis transfer is usually only energetically favorable if the aprotic solvent efficiently solvates the alkali metal ion.\nEffective solvents are those that bind to the alkali metal cation: [diethyl ether](https://bliptext.com/articles/diethyl-ether) < [THF](https://bliptext.com/articles/tetrahydrofurane) < [1,2-dimethoxyethane](https://bliptext.com/articles/dimethoxyethane) < [HMPA](https://bliptext.com/articles/hmpa).\nIn principle any unsaturated molecule can form a radical anion, but the antibonding orbitals are only energetically accessible in more extensive conjugated systems.\nEase of formation is in the order [benzene](https://bliptext.com/articles/benzene) < [naphthalene](https://bliptext.com/articles/naphthalene) < [anthracene](https://bliptext.com/articles/anthracene) < [pyrene](https://bliptext.com/articles/pyrene), etc. Salts of the radical anions are often not isolated as solids but used in situ.\nThey are usually deeply colored.\n\n# Other examples\n[Cyclooctatetraene](https://bliptext.com/articles/cyclooctatetraene) is reduced by elemental [potassium](https://bliptext.com/articles/potassium) to the dianion.\nThe resulting dianion is a 10-pi electron system, which conforms to the [Huckel rule](https://bliptext.com/articles/huckel-rule) for [aromaticity](https://bliptext.com/articles/aromaticity).\n[Quinone](https://bliptext.com/articles/quinone) is reduced to a [semiquinone](https://bliptext.com/articles/semiquinone) radical anion.\n[Semidiones](https://bliptext.com/articles/semidione) are derived from the reduction of dicarbonyl compounds.\n\n# Reactions\n\n## Redox\nThe pi-radical anions are used as reducing agents in specialized syntheses.\nBeing soluble in at least some solvents, these salts act faster than the alkali metals themselves.\nThe disadvantages are that the polycyclic hydrocarbon must be removed.\nThe reduction potential of alkali metal naphthalene salts is about 3.1 V (vs Fc+/0).\nThe reduction potentials of the larger systems are lower, for example acenaphthalene is 2.45 V. Many radical anions are susceptible to further reduction to dianions.\n\n## Protonation\nAddition of a proton source (even water) to a radical anion results in protonation, i.e. the sequence of reduction followed by protonation is equivalent to [hydrogenation](https://bliptext.com/articles/hydrogenation).\nFor instance, the anthracene radical anion forms mainly (but not exclusively) 9,10-dihydroanthracene.\nRadical anions and their protonation are central to the [Birch reduction](https://bliptext.com/articles/birch-reduction).\n\n## Coordination to metal ions\nRadical anions of polycyclic aromatic compounds function as ligands in [organometallic chemistry](https://bliptext.com/articles/organometallic-chemistry).\n\n# Radical cations\nCationic radical species are much less common than the anions.\nDenoted, they appear prominently in mass spectrometry.\nWhen a gas-phase molecule is subjected to [electron ionization](https://bliptext.com/articles/electron-ionization) one electron is abstracted by an electron in the electron beam to create a radical cation M+..\nThis species represents the [molecular ion](https://bliptext.com/articles/molecular-ion) or parent ion.\nA typical [mass spectrum](https://bliptext.com/articles/mass-spectrum) shows multiple signals because the molecular ion fragments into a complex mixture of ions and uncharged radical species.\nFor example, the [methanol](https://bliptext.com/articles/methanol) radical cation fragments into a [methenium](https://bliptext.com/articles/methenium) cation CH3+ and a [hydroxyl](https://bliptext.com/articles/hydroxyl) radical.\nIn [naphthalene](https://bliptext.com/articles/naphthalene) the unfragmented radical cation is by far the most prominent peak in the mass spectrum.\nSecondary species are generated from [proton](https://bliptext.com/articles/hydrogen-ion) gain (M+1) and [proton](https://bliptext.com/articles/hydrogen-ion) loss (M-1).\nSome compounds containing the [dioxygenyl](https://bliptext.com/articles/dioxygenyl) cation can be prepared in bulk.\n\n## Organic conductors\nRadical cations figure prominently in the chemistry and properties of [conducting polymers](https://bliptext.com/articles/conducting-polymer).\nSuch polymers are formed by the oxidation of [heterocycles](https://bliptext.com/articles/heterocycle) to give radical cations, which condense with the parent heterocycle.\nFor example, [poly[pyrrole](https://bliptext.com/articles/pyrrole)](https://bliptext.com/articles/poly[pyrrole](https://bliptext.com/articles/pyrrole)) is prepared by oxidation of [pyrrole](https://bliptext.com/articles/pyrrole) using [ferric chloride](https://bliptext.com/articles/ferric-chloride) in methanol:\nOnce formed, these polymers become conductive upon oxidation.\n[Polarons](https://bliptext.com/articles/polaron) and [bipolarons](https://bliptext.com/articles/bipolaron) are radical cations encountered in doped conducting polymers.","revisionCount":0},"hasMore":false,"nextCursor":null}

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