**4. Conclusion**

ESR is a suitable tool for investigating the kinetics and thermodynamics of exchange reactions. Such reactions are often used to model elementary processes like electron transfer and diffusion. Electron Self- and spin exchange rate constants can be measured quite accurately and from their temperature and pressure dependencies, the corresponding activation energies and volumes can be determined. The obtained experimental data may be interpreted within the framework of the appropriate theories, e.g. Marcus theory in the case of electron transfer.

Due to their great stability and the relative simplicity of their ESR spectra, nitroxides are prime candidates in ESR line broadening experiments.
