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| A '''free-radical reaction''' is any [[chemical reaction]] involving [[free radical]]s. This reaction type is abundant in [[organic reaction]]s.
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| Two pioneering studies into free radical reactions have been the discovery of the [[triphenylmethyl radical]] by [[Moses Gomberg]] (1900) and the '''lead-mirror experiment'''<ref>''Über die Darstellung von freiem Methyl'' [[Berichte der deutschen chemischen Gesellschaft]] (A and B Series) Volume 62, Issue 5 , Pages 1335–47 Fritz Paneth, Wilhelm Hofeditz {{DOI|10.1002/cber.19290620537}}</ref> described by [[Friedrich Paneth]] in 1927. In this last experiment [[tetramethyllead]] is [[chemical decomposition|decomposed]] at elevated temperatures to methyl radicals and elemental lead in a [[quartz]] tube. The gaseous methyl radicals are moved to another part of the chamber in a carrier gas where they react with lead in a mirror film which slowly disappears.
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| When radical reactions are part of [[organic synthesis]] the radicals are often generated from [[radical initiator]]s such as peroxides or azobis compounds. Many radical reactions are chain reactions with a [[chain initiation]] step, a [[chain propagation]] step and a [[chain termination]] step. [[Reaction inhibitor]]s slow down a radical reaction and [[radical disproportionation]] is a competing reaction. Radical reactions occur frequently in the gas phase, are often initiated by light, are rarely acid or base catalyzed and are not dependent on polarity of the reaction medium.<ref>[http://scienceworld.wolfram.com/chemistry/FreeRadicalReaction.html Free Radical Reaction – from Eric Weisstein's World of Chemistry<!-- Bot generated title -->]</ref> Reactions are also similar whether in the gas phase or solution phase.<ref>{{JerryMarch}}</ref>
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| == Kinetics ==
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| The [[chemical kinetics]] of a radical reaction depend on all these individual reactions. In [[Steady state (chemistry)|steady state]] the concentrations of initiating (I<sup>.</sup>) and terminating species T<sup>.</sup> are negligent and rate of initiation and rate of termination are equal. The overall [[reaction rate]] can be written as:<ref name=carey>''Advanced Organic Chemistry'' F.A. Carey R.J. Sundberg ISBN 0-306-41198-9</ref>
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| :<math>\ rate = k_{obs}[I]^{3/2} \,</math>
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| with a [[broken order reaction|broken-order]] dependence of 1.5 with respect to the initiating species.
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| The reactivity of different compounds toward a certain radical is measured in so-called competition experiments. Compounds bearing [[carbon–hydrogen bond]]s react with radicals in the order [[primary carbon atom|primary]] < [[secondary carbon atom|secondary]] < [[tertiary carbon atom|tertiary]] < [[benzyl]] < [[allyl]] reflecting the order in C–H [[bond dissociation energy]]<ref name=carey/>
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| Many stabilizing effects can be explained as [[resonance effect]]s, an effect specific to radicals is the [[captodative effect]].
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| == Reactions ==
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| The most important reaction types involving free radicals are:
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| * [[Free-radical substitution]], for instance [[free-radical halogenation]] and [[autoxidation]].
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| * [[Free-radical addition]] reactions
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| * [[Intramolecular]] free radical reactions (substitution or addition) such as the [[Hofmann–Löffler reaction]] or the [[Barton reaction]]
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| * Free radical [[rearrangement reaction]]s are rare compared to rearrangements involving carbocations and restricted to [[aryl]] migrations.
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| * Fragmentation reactions or [[homolysis (chemistry)|homolysis]], for instance the [[Norrish reaction]], the [[Hunsdiecker reaction]] and certain [[decarboxylation]]s. For fragmentations taking place in mass spectrometry see [[mass spectrum analysis]].
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| * [[Electron transfer]]. An example is the decomposition of certain [[perester]]s by [[copper|Cu(I)]] which is a [[one-electron reduction]] reaction forming Cu(II), an [[alkoxy]] oxygen radical and a [[carboxylate]]. Another example is [[Kolbe electrolysis]].
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| * [[Radical-nucleophilic aromatic substitution]] is a special case of [[nucleophilic aromatic substitution]].
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| * Carbon–carbon coupling reactions, for example [[manganese-mediated coupling reactions]].
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| it can be formed by photochemical reaction and thermal fission reaction or by oxidation reduction reaction
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| Specific reactions involving free radicals are [[combustion]], [[pyrolysis]] and [[Cracking (chemistry)|cracking]]<ref>Robert T. Morrison, Robert N. Boyd, and Robert K. Boyd, Organic Chemistry, 6th edition (Benjamin Cummings), 1992, ISBN 0-13-643669-2</ref>
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| ==See also==
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| * [[Radical clock]]
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| ==References==
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| {{Reflist}}
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| [[Category:Organic chemistry]]
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| [[Category:Free radical reactions]]
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