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 GR 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.