Resonance stabilized radicals thermochemistry

Several other noteworthy features of resonance-stabilized radical thermochemistry are ... 

Use of the thermochemistry discussed above allows rough estimation of reaction enthalpy for a wide range of reactions involving resonance-stabilized radicals. Furthermore, reaction entropies and heat capacities may often be estimated to a good level of accuracy (+ 1-2 cal/mol K) (7b). Hence, equilibrium constants may be estimated to a level of accuracy determined primarily by the uncertainty in reaction enthalpy. 

The reaction of ODC6 DO to form a five member ring ODY(C5 )CDO radical has the lowest barrier of only 15 kcal mol This ODY(C5 )CDO radical can beta scission (eliminate) a formyl radical with a 37 kcal mof barrier to form cyclopentadiene-one (ODY(C5)). It is important to note that resonantly stabilized radicals of cyclopentadiene and cyclopentadiene-ones are formed in the oxidation steps of aromatic systems. Their thermochemistry, reaction paths and kinetics all need to be analyzed for the inclusion of aromatics in combustion mechanisms. 

The radical abstraction activation energy (Ei) was estimated from the thermochemistry (Ai/° i = 12.6 kcal.mole ) and a back abstraction activation energy of, = 9 kcal.mole Other estimates follow from the initiation reaction thermodynamics and by analogies with similar reactions . The chain carrier is the resonance stabilized, 2-methyl ally radical, and this should give the slowest (maximally inhibited) chain. From the steady state, one obtains... 

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