EPR and ENDOR Investigations of Dynamic Processes in Sterically Overcrowded Phenoxyl-Type Galvinoxyl Radicals

Article abstract of DOI:10.1002/mrc.1260260513

The syntheses of tert-butylgalvinol with perdeuteriated tert-butyl groups and 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.Deuteration 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 (ΔH^*=21.8 kJ/mol, ΔS^*=-32 J/molK).The biradical 1,4-bicyclo<2.2.2>octanebisgalvinoxyl exhibits strong scalar and dipolar electron interactions (D=97 MHz). KEY WORDS EPR ENDOR Galvinoxyls Deuteration Dynamic processes Biradicals.