Axially Chiral Stable Radicals: Resolution and Characterization of Blatter Radical Atropisomers

Atropisomers of three Blatter radicals were obtained by the addition of 8-substituted 1-naphthyllithiums to 3-phenyl and 3-t-butylbenzo[e][1,2,4]triazine and separated by chiral high-performance liquid chromatography. Their absolute configurations were assigned by a comparison of experimental and time-dependent density functional theory calculated electronic circular dichroism spectra. The free energy of activation, ΔG‡298, and the half life of racemization, t1/2, at 298 K were determined at ∼25 kcal mol–1 and <130 h, respectively. Intramolecular π–π interactions in radicals were evident from single-crystal X-ray diffraction, density functional theory, and electrochemical analyses.