Electron spin resonance detection of the intermediate radicals occurring in homolytic aromatic substitutions of furan and thiophen

Abstract

A number of radicals generated by photolysis add to furan and thiophen giving radicals involved in homolytic aromatic substitution: the corresponding e.s.r. spectra were observed. Photolysis of (PhCOO)₂ in furan or thiophen gives the spectra of both (A) and (B). On the other hand photolysis of (MeCOO)₂ in furan gave the spectrum [graphic omitted] of (C) at –110° but that of (D) at higher temperature (–10°). The interpretation of the a_H hyperfine splitting constants suggests that the structure of these radicals is not planar. They seem rather to prefer envelope-like conformations with the substituents either in pseudoaxial or in pseudoequatorial positions or in equilibrium between the two, depending on the substituent.