Factors affecting the stability and equilibria of free radicals. Part 11. 1-Benzoyl-2,2-bis-(3,5-di-t-butylphenyl)hydrazyl and its temperature-dependent electron spin resonance spectrum

Abstract

The title free radical was prepared by oxidizing the corresponding hydrazine with lead tetra-acetate in benzene or toluene. Its e.s.r. spectrum undergoes reversible changes in the temperature range –90 to +60 °C. Simulated e.s.r. spectra indicate that the two di-t-butylphenyl groups are non-equivalent owing to restricted rotation around the N–N bond at low temperatures, but at 60 °C these two aryl groups become equivalent. The ΔG^‡ value of the rotation barrier is about 31 kJ mol^–1 in the temperature range –30 to +50 °C.