Survey of Results and Techniques

One of the earliest examples of CIDNP is the proton resonance emission of benzene observed during thermolysis of dibenzoylperoxide (I) in cyclohexanone which proceeds predominantly via (1) (see Sect. 4.1). 

This emission develops after the insertion of a solution of I into the preheated probe of the spectrometer and may be followed for several minutes (Fig. 1). Later on it changes into a normal absorption peak as the reaction is completed. This time dependence indicates that the benzene is formed with excess populations of the energetically higher nuclear Zeeman levels, i.e. with a specific nuclear polarization, and that it relaxes to thermal equilibrium after formation. 

Another example of early CIDNP phenomena is given in Fig. 2 (lower part). Emissions and enhanced absorptions appear in the vinyl proton resonances of 

1-butene (A, B, C) and isobutylene (D) during the reaction of tert.-butyllithium with n-butylbromide 

The upper part of Fig. 2 gives the spectrum after completion of the reaction. 

---