Cu(I) which is a one-electron reduction reaction forming Cu(II), an alkoxy oxygen radical and a carboxylate. Another example is Kolbe electrolysis. Radical-nucleophilic aromatic substitution is a special case of nucleophilic aromatic substitution. Carbon–carbon coupling reactions, for example manganese-mediated coupling reactions. Elimination reactions Free radicals can be formed by photochemical reaction and thermal fission reaction or by oxidation reduction reaction. Specific reactions involving free radicals are combustion, pyrolysis and cracking. Free radical reactions also occur within and outside of cells, are injurious, and have been implicated in a wide range of human diseases (see 13-Hydroxyoctadecadienoic acid, 9-hydroxyoctadecadienoic acid, reactive oxygen species, and Oxidative stress) as well as many of the maladies associated with ageing (see ageing). See also Radical clock References Organic chemistry