ESR Study of Free Radicals Produced by Irradiation in Benzene and Its Derivatives

Abstract

Benzene and some of its mono‐ and di‐substituted derivatives including toluene, chlorobenzene, benzoic acid, phenylcyclohexane, polystyrene, and xylenes were irradiated in their solid state at —196°C. After the irradiation their ESR spectra were measured at that temperature and also up to their melting points. The spectrum of benzene consisted of two components. One was a main triplet (splitting 47.5 G) with a quartet substructure (splitting 10.4 G), each quartet showing further fine (probably triplet) splitting of ∼2.5 G, and it was assigned to cyclohexadienyl radical C₆H₇·. When the temperature was raised this spectrum showed a marked narrowing from about —173°C where the C₆ reorientation of the benzene molecule sets in. At the same time the radical began to diminish, and decayed out at —32°C, which is far below the melting point. The other component of the spectrum was a singlet of 25‐G width at the maximum slope, and was assigned to phenyl radical C₆H₅·. This component decayed out at 0°C. The spectra of the benzene derivatives were triplet, quite similar to that of benzene, and were interpreted to be due to the radicals produced as a result of hydrogen addition to the benzene ring. The G_R values determined at —196°C for benzene, cyclohexane, their 1:1 mixture, and phenylcyclohexane were 0.14, 5.04, 2.4 and 0.66, respectively. It is concluded that in the case of phenylcyclohexane some energy‐transfer process may occur from the cyclohexyl ring to the phenyl ring.