EPR and ENDOR investigations of dynamic processes in sterically overcrowded phenoxyl‐type galvinoxyl radicals

Abstract

Abstract The syntheses of tert ‐butylgalvinol with perdeuteriated tert ‐butyl groups and of 1,4‐bicyclo[2.2.2]octanebisgalvinol are described. The EPR and ENDOR spectra of the corresponding galvinoxyl monoradicals reveal selective line broadening due to dynamic processes associated with hindered internal rotation of the phenoxy rings. Deuteriation of the central tert ‐butyl group in tert ‐butylgalvinoxyl gives rise to a substantial decrease of EPR line widths, allowing the determination of the kinetic parameters by means of line‐shape analyses (Δ H ≠ = 21.8 kJ mol −1 , Δ S ≠ = −32 J mol −1 K −1 ). The biradical 1,4‐bicyclo[2.2.2]octanebisgalvinoxyl exhibits strong scalar and dipolar electron interactions ( D = 97 MHz).