Radical clock

Cyclizations of alkyl radicals are suitable reactions

The radical clock is a method of chemical reaction kinetics for the indirect measurement of rate constants of reactions of a radical . To apply this method, the radical must have a unimolecular pathway, for which the rate constant is well known. This is often the case with alkyl radicals . This so-called clock reaction is often a ring-closing , ring-opening or rearrangement reaction or electron transfer . When applying the method, this reaction is in competition with the (mostly) bimolecular reaction, whose rate constant one is interested in. The branching ratio between both reactions is then determined by analyzing the reaction products. It depends on the concentration of the reactant (to be chosen appropriately) . The advantage of the method is the relative simplicity of the product analysis, e.g. B. gas or liquid chromatography or NMR spectroscopy , so that if a clock reaction is available , several bimolecular reactions are often connected to it.

A possible complication is the reversibility of the clock reaction , which can possibly be defused by a further reaction. In such cases it is necessary to determine the branching ratio for different concentrations and to prepare a reaction mechanism .

Individual evidence

1. ^ Krzysztof Matyjaszewski, Thomas P. Davis: Handbook of Radical Polymerization. Wiley, 2002, p. 101 ( limited preview in Google Book search).