Introduction - Formation of degenerate branching agents

In 1968 Fish [119] proposed an alkylperoxy isomerization theory that explains the temperature dependence of the ignition delays and the complex spectrum of products that can be obtained in hydrocarbon oxidation. Once formed the ROO radical can under go an internal isomerization. Cleavage of the resulting R OOH (or QOOH) radical is a chain propagating step leading to generation of a number of different products and an OH radical. Alternatively at low temperatures the addition of O2 can compete with unimolecular dissociation. 

The resulting radical species can undergo a number of reactions including the formation of the hydroperoxide degenerate branching agent. 

However, direct studies of the R + O2 equilibrium, of the type described in Section 2.6.2, produce values for the equilibrium constant over an order of magnitude different from the thermochemical estimates affecting the absolute values of the isomerization rates. Pilling and coworkers [122, 123] devised a time resolved equivalent of Baldwin and Walker s experiment (Fig. 2.37b) to directly measure the isomerization rate for the neopentyl radical. This technique is described in Section 2.7.2. The results of the direct studies are shown to be compatible with the earlier indirect work and can be used to scale the results of Baldwin and Walker. The relationship between isomerization rate and structure is discussed in Section 2.7.3. 

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