An electron spin resonance study of the formation of radical cations in FSO3H/SO2 solution

Abstract

Arenes which in FSO₃H/SO₂ solution show the n.m.r. spectra of the carbocations resulting from proton addition, also show the e.s.r. spectra of the radical cations resulting from electron loss. This provides a convenient technique for studying the e.s.r. spectra of radical cations in fluid solution down to ca. 180 K.

A few compounds show special behaviour. 2,3-Dihydrophenylene and acenaphthene give rise to spectra which show that protons have been replaced, and which have a high g value. It is proposed that this results from the introduction of a disulphide bridge across the peri positions. Stilbene and diphenylacetylene show spectra with ‘normal’g values, but which are different from the spectra previously ascribed to the corresponding radical cations, and which appear to imply that there are non-equivalent ortho protons.