Reaction 11a proceeds according to the Russell-mechanism, where a tetraoxide intermediate is formed which decomposes to yield non-radical products: an alcohol, ketone and singlet oxygen. The other bimolecular peroxyl radical termination reaction, reaction 11b, leads to a peroxide cross-link. This reaction is proposed to proceed also via a tetraoxide intermediate, some speculation regarding the validity of that proposal remains, however.[26, 27] In Scheme 1.2 the tetraoxide intermediate and the course of termination reactions 11a and 11b is shown.