Primary mechanism for the pyrolysis of neopentane

A primary mechanism uses as reactants the molecules included in the reaction load, i.e. neopentane in the present case, and free radicals arising from it, with the exclusion of the products which are formed. If the reactions of the primary products are taken into account, this is then a secondary mechanism, which is necessarily more complicated. On principle, a primary mechanism only takes the experimental results at conversion equal to zero into account, which can therefore only be obtained by extrapolation. It is 

This mechanism involves a closed sequence, or chain, consisting of reactions (52) and (53). The two free radical chain carriers are the neopentyl radical and the 

Applying the QSSA globally to the radicals gives the following relationship  

The factors 2 indicate that the initiation (48) creates 2 free radicals and that the termination (54) makes 2 disappear. The following expression for the concentration of the methyl radicals is thus obtained  

It is important not to forget that the rate constant k 4 varies with the pressure, which is indicated by the notation (+M) in equation (54). 

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