Initiation can occur via several different pathways, either metal mediated or not.
Steps 1 and 2 in Scheme 1.1 are often proposed as the initiation steps in non-metal-
mediated autoxidation. Step 1 is the reaction of some arbitrary initiating species with
the substrate, directly forming a carbon-centred radical. Reaction 2 is the thermal
homolytic decomposition of a hydroperoxide, which only plays a significant role at
elevated temperatures. In metal-mediated initiation, the initiation of radical chains
predominantly occurs through steps 3 to 6. Reactions 3 and 4 are the so-called Haber-Weiss reactions, originally proposed for the decomposition of peroxide by iron in aqueous
media.