MEASUREMENT OF THE C-13 HYPERFINE TENSORS FOR CUBYL AND RELATED BRIDGEHEAD RADICALS

C-13 hyperfine features have been detected by electron paramagnetic re sonance (EPR) spectroscopy from a range of bridgehead radicals followi ng gamma-irradiation of the corresponding bromides at 77 K. For cubyl and its 4-methoxycarbonyl derivative, both parallel and perpendicular components of the C-13 tensor were resolved, but only the parallel com ponents could be detected for the 4-bromo derivative. The full C-13 te nsors were also obtained for bicyclo[2.2.1 ]heptyl and tricyclo[3.1.1. 0(3.6)]heptyl radicals, but for bicyclo[2.2.1]hexyl, bicyclo[2.2.2]oct yl and bicyclo[1.1.1]pentyl radicals only the parallel components were apparent, the perpendicular regions being obscured by other signals. A linear correlation is found between A(parallel-to) and the one-bond C-H (1J(C-H)) coupling in the nuclear magnetic resonance (NMR) spectra of the parent bridgehead alkanes and is used in the estimation of iso tropic coupling constants for the bridgehead radicals, even in those c ases where A(perpendicular-to) is unknown.