Thermochemistry of radical interactions

Benson and Shaw [101] have calculated heats for formation and bond strengths for many peroxides, polyoxides, and their precursor radicals, from which we can estimate the heats of reaction of the important interaction (termination) steps. For terminations of Me02-, the important 

Formation of RO from R02 is only slightly exothermic, in contrast to 

Equilibrium enthalpies and entropies for reactions (171) and (—171), the reversible dissociation of tetroxide to R02-, have been measured with good precision between —140 and —80°C for several f-R04R using low temperature ESR to monitor changes in the concentration of R02 [11, 117,128]. Values for AHlnl and AS171 and calculated values of Ktll are summarized in Table 20. 

The relatively small differences in Ktll suggest that any differences in the observed values of 2kt must originate in the irreversible dissociation of R04R to RO, reaction (173) that is kinetic, not thermochemical, properties govern the overall rate of termination. 

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