Spin chemistry induced dynamic nuclear polarization

In the case of transient species with unpaired electrons such as free radicals, and the triplet states of carbenes or nitrenes, electron spin resonance (ESR) spectroscopy can provide unique evidence about the structure of the intermediate. Useful information about intermediates in reactions involving radical pair coupling can also be obtained by a technique known as chemically-induced dynamic nuclear polarization (CIDNP). However, detailed discussions of ESR and CIDNP are outside the scope of this book and for further information suitable text books on physical organic chemistry or the references given in the Further Reading section should be consulted. 

The first reports of the observation of transient emission and enhanced absorption signals in the H-n.m.r. spectra of solutions in which radical reactions were taking place appeared in 1967. The importance of the phenomenon, named Chemically Induced Dynamic Nuclear Spin Polarization (CIDNP), in radical chemistry was quickly recognized. Since that time, an explosive growth in the number of publications on the subject has occurred and CIDNP has been detected in H, C, N, and P as well as H-n.m.r. spectra. Nevertheless, the number of groups engaged in research in this area is comparatively small. This may be a consequence of the apparent complexity of the subject. It is the purpose of this review to describe in a quahtative way the origin of CIDNP and to survey the published applications of the phenomenon in... 

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