Cyclic ketones, CIDNP

In the photolysis of several cyclic ketones the recent observation of CIDNP in 13C Fourier-transform n.m.r. is taken as good evidence for the involvement of biradical species in the reactions.426 Other reactions studied with n.m.r. CIDNP techniques include the photolysis of some simple alkanones,487 some decarboxylation reactions,428 in dyestuffs,429 in electron-transfer reactions in aromatic ketones,430 in methyl diazoacetate,431 and in acylsilane432 and cleavage of... 

Paramagnetic species possessing two unpaired electrons (biradicals, carbenes, and their analogues) have been intensively studied using CIDNP techniques in high and low magnetic fields. The involvement of biradicals in organic and biochemical reactions is postulated in a number of cases, but the physical methods (EPR, laser spectroscopy) have allowed the detection of their formation predominantly in the photolysis of cyclic ketones. These species have also served as models for detailed studies of CIDNP peculiarities for biradicals, as well as the distinction of these effects from the case of free radicals. 

Reference data on biradicals of cyclic ketones point to the appearance of CIDNP effects in a wide range of magnetic field strengths. The manifestations of various mechanisms of CIDNP formation depend on the structure of the biradical. 

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