STERICALLY HINDERED FREE-RADICALS .22. DIMERIZATION AND EPR SPECTROSCOPY OF INDANEDIONYL AND 9-ACYLFLUORENYL RADICALS

2-Phenylindanedionyl radicals 5a, their p- and o-monosubstituted deriv atives and related compounds 5b-h recombine by C-C bond formation givi ng 6a-h. In contrast, o-substituted derivatives 5i-k and the 2-tert-bu tylindanedionyl radicals 5I react to give the enol ethers 10a-d by C-O coupling. The EPR data indicate that the substituents are more bulky in 5i-I than in 5a-h. From the proton splitting constants it is conclu ded that 5a is planar and 5h nearly planar (twist angle of the phenyl group ca. 30-degrees). The phenyl group in 5i is twisted considerably with an angle of about 50-degrees. The g values of 5i-k are larger tha n those of 5a-h indicating a higher spin density in the carbonyl group s.9-Acylfluorenyl radicals 12b-c, representing the planar conformation s of diarylmethyl radicals 1 c, d, give no enol ethers like 4, but rec ombine by C-C bond formation yielding 13b-c. Their g values indicate t hat the acyl groups are twisted out of the radical plane.