Factors Affecting the Stability and Equilibria of Free Radicals. 14. Unexpected Spin Densities in 1-(Trifluoroacetyl)-2,2-diarylhydrazyl Revealed by 15N Labeling

Article abstract of DOI:10.1021/jo00228a006

1-(Trifluoroacetyl)-2,2-bis(3,5-di-tert-butylphenyl)hydrazyl and its congener labeled at the dicoordinated 1-nitrogen atom with 15N were prepared.ESR spectra of solutions of both compounds were recorded and hyperfine coupling constants determined by optimizing simulated spectra.Unlike all other 1,2,2-triarylhydrazyls which have been investigated, the hyperfine coupling constant for the dicoordinated nitrogen is lower (0.7 mT) than that for the tricoordinated nitrogen (1.0 mT) in this free radical.This striking result raises questions about the mode of trifluoroacetyl group participation in ? electron delocalization.