Abstract
Radical chain reactions are commonly initiated through the thermal or photochemical activation of purpose-built initiators, through photochemical activation of substrates, or through well-designed redox processes. Where radicals come from in the absence of these initiation strategies is much less obvious and are often assumed to derive from unknown impurities. In this situation, molecule-induced radical formation (MIRF) reactions should be considered as well-defined alternative initiation modes. In the most general definition of MIRF reactions, two closed-shell molecules react to give a radical pair or biradical. The exact nature of this transformation depends on the σ- or π-bonds involved in the MIRF process, and this Minireview specifically focuses on reactions that transform two σ-bonds into two radicals and a closed-shell product molecule.