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EPR and ENDOR investigations of dynamic processes in sterically overcrowded phenoxyl‐type galvinoxyl radicals
Author(s) -
Von Gersdorff J.,
Kirste B.,
Niethammer D.,
Harrer W.,
Kurreck H.
Publication year - 1988
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260260513
Subject(s) - chemistry , electron paramagnetic resonance , steric effects , spectral line , bicyclic molecule , radical , photochemistry , kinetic energy , dipole , line width , crystallography , nuclear magnetic resonance , stereochemistry , organic chemistry , physics , quantum mechanics , astronomy , optics
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).