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Radical (chemistry)
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<p>In <a href="/facts/Chemistry/SrNqkGVm">chemistry</a>, a radical, also known as a free radical, is an <a href="/facts/Atom/69syB8dH">atom</a>, <a href="/facts/Molecule/N9ljSfFq">molecule</a>, or <a href="/facts/Ion/wrbwhF3z">ion</a> that has at least one <a href="/facts/Unpaired_electron/yJTW1urJ">unpaired valence electron</a>. With some exceptions, these unpaired electrons make radicals highly <a href="/facts/Chemical_reaction/GpqWlKrz">chemically reactive</a>. Many radicals spontaneously <a href="/facts/Dimer_(chemistry)/mU64PnEq">dimerize</a>. Most organic radicals have short lifetimes. </p><p>A notable example of a radical is the <a href="/facts/Hydroxyl_radical/XafpvqK5">hydroxyl radical</a> (HO·), a molecule that has one unpaired electron on the oxygen atom. Two other examples are <a href="/facts/Triplet_oxygen/uAE4t017">triplet oxygen</a> and <a href="/facts/Methylene_radical/vIPU9NXl">triplet carbene</a> (꞉CH2) which have two unpaired electrons. </p><p>Radicals may be generated in a number of ways, but typical methods involve <a href="/facts/Redox_reaction/Pyd5RVcj">redox reactions</a>. <a href="/facts/Ionizing_radiation/vw0d9GaT">Ionizing radiation</a>, heat, electrical discharges, and <a href="/facts/Electrolysis/pU75nCDI">electrolysis</a> are known to produce radicals. Radicals are intermediates in many chemical reactions, more so than is apparent from the balanced equations. </p><p>Radicals are important in <a href="/facts/Combustion/ohQoWj8z">combustion</a>, <a href="/facts/Atmospheric_chemistry/EbmISm33">atmospheric chemistry</a>, <a href="/facts/Polymerization/1hmBz7Ur">polymerization</a>, <a href="/facts/Plasma_(physics)/1d3btMVU">plasma</a> chemistry, <a href="/facts/Biochemistry/fa2pWEBp">biochemistry</a>, and many other chemical processes. A majority of natural products are generated by radical-generating enzymes. In living organisms, the radicals <a href="/facts/Superoxide/2X2sQocn">superoxide</a> and <a href="/facts/Nitric_oxide/UvhdvDzp">nitric oxide</a> and their reaction products regulate many processes, such as control of vascular tone and thus blood pressure. They also play a key role in the intermediary metabolism of various biological compounds. Such radicals are also messengers in a process dubbed <a href="/facts/Redox_signaling/bMPkHojL">redox signaling</a>. A radical may be trapped within a <a href="/facts/Cage_effect_(chemistry)/UJMmF27E">solvent cage</a> or be otherwise bound. </p>