Basic Radical Chemistry General Aspects of Synthesis with Radicals

Basic Radical Chemistry General Aspects of Synthesis with Radicals 

Radicals are species with at least one unpaired electron, which, in contrast to organic anions and cations, react easily with themselves in bond-forming reactions. In the liquid phase, most of these reactions occur with diffusion-controlled rates. Radical-radical reactions can be slowed only if radicals are stabilized by electronic effects (stable radicals) or shielded by steric effects (persistent radicals). However, these effects are not strong enough to prevent diffusion-controlled recombination of, for example, benzyl radicals or tert-butyl radicals.1 Only in extreme cases are the radical or di-tert-butylmethyl radical recombination rates low.2 While the recombination rates of the triphenyl-methyl radical is reduced due to both steric and radical stabilizing effects, the steric effect alone slows the recombination of the di-/t /-/-butyl methyl radical. Since neither of the radicals have C-H bonds (I to the radical centre, disproportionation reactions, in which the hydrogen atom is transferred, cannot occur. 

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