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RADICAL ANIONS 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 Proton source the radical anion is protonated and effectively hydrogenated like in the Birch Reduction .
An example of a non-carbon radical anion is the Superoxide anion, formed by transfer of one electron to an Oxygen molecule. A very effective way to remove any traces of water from . Cyclooctatetraene is reduced by elemental Potassium directly to the dianion (skipping the radical anion state) because the 10 electron system is an aromat. Quinone is reduced to a Semiquinone radical anion. Semidione s are derived from the reduction of dicarbonyl compounds. RADICAL CATIONS Cationic radical species do also exist but are much less stable. They appear prominently in Mass Spectroscopy . 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+.. 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 CH3+ 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 Proton gain (M+1) and proton loss (M-1). Polaron s and Bipolaron s are radical cations encountered in doped Conducting Polymer s. |
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