Chemically induced dynamic nuclear radical fragmentations

Further evidence for the formation of alkene radical cations derives from the work of Giese, Rist, and coworkers who observed a chemically induced dynamic nuclear polarization (CIDNP) effect on the dihydrofuran 6 arising from fragmentation of radical 5 and electron transfer from the benzoyl radical within the solvent cage (Scheme 6) [67]. 

Chemically induced dynamic nuclear polarization (CIDNP) has been used to discriminate radical and nonradical processes in cycloadditions of electron-rich alkenes and electron-poor carbonyl components <1998MI9>. Spectroscopic observation of the fragmentation of an oxetane radical anion revealed the generation of the most stable alkene radical <2003JOC10103, 2006PPS51>. Transient absorption spectroscopy has been employed to monitor the Paterno-Biichi cycloaddition of benzophenone and furan <2004JA2838>. 

The El-induced fragmentation of gaseous [4 + 2]- and [2 + 2]dicyclopentadiene radical cations has been studied by Roth and coworkers using Fourier transform ion cyclotron resonance mass spectrometry, and compared to the cleavage of these ions in solution using chemically induced dynamic nuclear polarization (CIDNP). Both in the gas and in the liquid phase, the isomers of the molecular ions formed by single C—C bond cleavage were observed. It is noteworthy that these distonic ions were termed non-vertical radical cations. 

Goez, M., Rozwadowski, J., and Marciniak, B., Photoinduced electron transfer, decarboxylation and radical fragmentation of cysteine derivatives a chemically induced dynamic nuclear polarization study, /. Am. Chem. Soc., 118, 2882, 1996. 

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