Radical pairs in redox reactions involving sterically hindered quinones and phenols

The review summarises the results of studies on the redox reactions involving sterically hindered quinones and pyrocatechols (phenols) occurring in glassy and single-crystal matrices. Exposure of these systems to light results in the transfer of a hydrogen atom or an electron from the phenol to the quinone accompanied by the formation of radical pairs, viz., two paramagnetic species existing in the triplet state. Studies of the transformations in single-crystal matrices enabled separation of the mechanisms of electron and hydrogen atom transfer. Synchronous transfer of two hydrogen atoms from two sterically hindered phenol molecules to o-benzoquinone is also possible. The bibliography includes 39 references.