Stereoelectronic effect at nitrogen in 2,6-di-tert-butyl-4-(N,N-disubstituted aminomethyl)phenoxyl radicals

Abstract

A variety of 2,6-di-tert-butyl-4-(N,N-disubstituted aminomethyl)phenoxyl radicals have been studied with respect to the para substituents’ and meta protons’ coupling constants observed in EPR and ENDOR experiments. For all molecules considered, restricted rotation dominates the spectroscopic features of the β-nuclei, and this plays a key role throughout the investigation. Based on the well-known McConnell–Heller equation, an empirical formula is proposed for analyzing the conformation at the α-carbon atom relative to the aroxyl plane. The results obtained reveal a strong stereoelectronic interaction between the β-nitrogen atom and the aromatic π-system. Hence, sterically unfavorable orientations are found to be preferred. The stereoelectronic interdependence is finally interpreted in terms of the generalized anomeric effect.