Assumptions in Radical Clock Studies

By the nature of the study, one often is required to make assumptions about the kinetics of clock reactions. The most important are (1) that one radical is an appropriate model for another and (2) that solvent effects for radical reactions can be approximated or ignored. 

The assumption that one radical is an appropriate model for another is most sound when one is using a clock to calibrate a bimolecular reaction and the local environment of the clock is similar to that of the radical of interest. For example, the rate constant found for reaction of the 5-hexenyl radical with a specific trapping agent should be a good approximation of the rate constant for reaction of another primary alkyl radical, especially one without substituents at C2. For most synthetic applications, the small errors in rate constants from this assumption will be unimportant. 

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