Measurement of the 13C hyperfine tensors for cubyl and related bridgehead radicals

Abstract

¹³ C hyperfine features have been detected by electron paramagnetic resonance (EPR) spectroscopy from a range of bridgehead radicals following γ-irradiation of the corresponding bromides at 77 K. For cubyl and its 4-methoxycarbonyl derivative, both parallel and perpendicular components of the ¹³C tensor were resolved, but only the parallel components could be detected for the 4-bromo derivative. The full ¹³C tensors 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]octyl 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_∥ 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 isotropic coupling constants for the bridgehead radicals, even in those cases where A_⊥ is unknown.