Preparation, structural characterization, and thermochemistry of an isolable 4-arylphenoxyl radical

Abstract

The preparation and full characterization of the 4-(nitrophenyl)- phenoxyl radical, 2,6-di- t butyl-4-(4′-nitrophenyl) phenoxyl radical ( t Bu 2 NPArO •) 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. (Figure Presented).