Carbon-13 hyperfine splittings and geometry at the radical center in bicyclo[2.2.1]hept-2-yl radicals

The paramagnetic adducts between organosilicon, -germanium, or -tin centered radicals and camphor and thiocamphor give ESR spectra sufficiently intense to allow the detection of the metal satellite lines as well as those of the naturally abundant I3C atoms. Although the magnitude of the hyperfine splitting from the CY carbon is indicative of a certain degree of pyramidalization at the radical center, the comparison with the same splittings for noncyclic radicals bearing similar substituents suggests that the observed nonplanarity in our bicyclo[2.2.l]hept-2-yls is essentially an effect of the substituent rather than of the bond-angle straining. INDO-MO calculations have also been carried out on model systems to obtain estimates of the degree of pyramidalization in the title radicals.