Biacetyl semidione radical

Most of the alcohol radicals have hyperfine coupling constants slightly dependent on both temperatures and solvents. Ayscough and McClung (220) have also studied in detail the effect of temperature variation on proton hyperfine splitting of the biacetyl semidione radical in the range 250-400 K. Livingston and Zeldes (156) observed... 

Norman and Pritchett nl> concluded that rapid tautomerization is involved in chemically generated biacetyl semidione radical the results Zeldes and Livingstone 171> observed with the photochemically generated radical differ). If this view is correct, product composition is determined in a step subsequent to H-abstraction. This is in agreement with the results obtained 130> with camphorquinone and aromatic aldehydes in benzene solution where the two isomeric products 61 and 62 were obtained in equal amounts in contrast to the results with -xylene. This... 

The inference that semidione radicals are intermediates in diketone photolysis has been widely accepted for many years since it provides a satisfactory rationale for the results observed in many reactions. Recently, direct evidence for the presence of these radicals has been obtained from flash photolysis 13> of benzil in alcoholic solvents and esr studie of irradiated solutions of biacetyl 12,171,183 camphorquinone 9,i83)> and other diones 183>. The related radical anions, generated by chemical means, have been studied extensively 5,3i,i3 ) and reports of the radical cations have also appeared m.137)... 

In fact, dimerization of semidione radicals appears to be important only with the open chain diones biacetyl and benzil (and possibly hexa-fluorobiacetyl). The diketopinacol [63, R = CaHs) was first obtained by... 

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