Kinetics of Inhibition and Retardation

Kinetics of Inhibition and Retardation.—The various reactions which may be brought about by an inhibiting or retarding substance, represented by Z, may be reduced to the following simple scheme  

Neglecting reaction (65) and considering only (62), (63), and (64), we have under steady-state conditions at an initiation rate Ri 

Solution of these equations for the two radical concentrations yields 

The rate of consumption of initiator should therefore be constant (i.e., of zero order) under given conditions. This deduction applies regardless of whether or not inhibitor radicals may undergo regeneration (reaction 63). It emphasizes again that the observation of a well-defined induction period of duration proportional to the amount of inhibitor initially present offers no assurance of a simple stoichiometric ratio between radicals stopped and inhibitor consumed. It will be observed that the rate of consumption of inhibitor, and therefore the length of the induction period for a given amount of inhibitor, depends exclusively on Ri if 2 = 0 if it depends also 

If cross termination reactions represented by (65) were to assume importance, the rate of consumption of inhibitor would not be independent of its concentration. The almost universal observation of proportionality between the length of the inhibition period and the amount of inhibitor available confirms our expectation that such processes are unimportant. 

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