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Updated: Apr 24, 2026

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Preparation, structural characterization, and thermochemistry of an isolable 4-arylphenoxyl radical
Thomas R Porter1, Werner Kaminsky, James M Mayer
1Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195-1700, United States.
Abstract:
The preparation and full characterization of the 4-(nitrophenyl)phenoxyl radical, 2,6-di-(t)butyl-4-(4'-nitrophenyl) phenoxyl radical ((t)Bu2NPArO(•)) is described. This is a rare example of an isolable and crystallographically characterized phenoxyl radical and is the only example in which the parent phenol is also crystallographically well-defined. Analysis of EPR spectra indicates some spin delocalization onto the secondary aromatic ring and nitro group. Equilibrium studies show that the corresponding phenol has an O-H bond dissociation free energy (BDFE) of 77.8 ± 0.5 kcal mol(-1) in MeCN (77.5 ± 0.5 kcal mol(-1) in toluene). This value is higher than related isolated phenoxyl radicals, making this a useful reagent for hydrogen atom transfer (HAT) studies. Additional thermochemical and spectroscopic parameters are also discussed.
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