Geometries, Spin Densities, Oxidative Power and pKa Values of Peroxyl Radicals

Geometries, Spin Densities, Oxidative Power and pKa Values of Peroxyl Radicals 

A similar gradation is observed, when 02 is the reductant. The rate of the reaction of the most powerful peroxyl radical, the acetylperoxyl radical, with 02 is close to diffusion-controlled [reaction (7) k 109 dm3 mol1 s Schuchmann and von Sonntag 1988], while the a-hydroxyethylperoxyl radical reacts with 02 merely with a rate constant near 107 dm3 mol 1 s1 (Bothe et al. 1983). 

The rate of H02 elimination from a-hydroxyalkylperoxyl radicals strongly depends on the flanking substituents that also govern the strength of the resulting C-0 double bond (for a compilation see von Sonntag and Schuchmann 1997). 

The 02 -elimination reactions maybe divided into three groups. Those peroxyl radicals that have an -OH or -NH function in the a-position make up the first group. Such peroxyl radicals play a major role in nucleobase peroxyl radical chemistry [cf. reactions (12) and (13)]. Upon deprotonation at die heteroatom by OH [reactions (10) and (12)], the peroxyl radical anion is formed (cf. the enhancement of the acidity of the functions a to the peroxyl group discussed above for the thermodynamics of the various equilibria that are involved in these reactions see Goldstein et al. 2002). As before, the driving force for the elimination reaction is the formation of a double bond [in addition to the energy gain by the formation of the stabilized 02- radical [cf. reactions (11) and (13)]. 

The peroxyl radical anion formed in reaction (10) has an immeasurably short ( 10 6 s ) lifetime, i.e ku is much larger than k 0 x [H20], and even at high [OH ] the rate of acetone formation is essentially given by kw x [OH ] (Bothe et al. 1977). The situation is similar for other a-hydroxyalkylperoxyl radical anions (Rabani et al. 1974 Ilan et al. 1976 Bothe et al. 1983) with the exception 

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