FREDERICK PETER SARGENT, MARSHALL GRANT BAILEY, and EDWARD MICHAEL GARDY. Can. J. Chern. 52, 2171 (1974).A comparison of both the e.s.r. spectra and the thermal stability of the radicals produced in y radiolysis and 185 nm photolysis of acetonitrile shows that the former are not free methyl radicals. The initial species formed by y radiolysis can be converted by photobleaching into a methyl radical weakly associated with a cyanide ion. The methyl radical of this CH3---CNpair decays via hydrogen abstraction, whereas the free methyl radicals produced by 185 n m photolysis of acetonitrile are quite stable at 77 K. We ascribe the low energy of activation for the hydrogen abstraction reaction in the y irradiated samples not primarily to quantum mechanical tunnelling but to perturbation by the cyanide ion.

The use of electron spin resonance (e.s.1.) to follow the course of a chemical reaction which does not involve paramagnetic intermediates is reported. The principle of the method is the conversion of the reaction product into a paramagnetic species which may be characterized by e.s.r. In the present example, photoconversion of ketones into radical anions is used to follow the successive displacement of fluorine from perfluorobenzophenone.On rapporte I'utilisation de la rksonnance paramagnktique Clectronique (1.p.e.) pour etablir la nature du chemin suivi par une reaction chimique qui n'implique pas d'inter~nediaires paramagnetiques. Le principe de la mithode est de transformer le produit de la reaction en une espece paramagnttique caractirisable par r.p.e. A titre d'exemple, on utilise la photoconversion de cetones en radicaux anions pour examiner les deplacements successifs du fluor en perfl~~orobenzophCnone.[Traduit par le journal]Can.

The ketyl radical is formed when solutions of perfluorobe~~zopheno~~e are photolyzed with 11.v. light. The radical was identified by electron spin resonance (e.s.r.) studies of the effects of solvent, tenlperati~re, chemical exchange, and deuteration on the spectra. Solvent ~n i x t~~r e s of cyclohexane and ethanol gave spectra which were very sensitive to the mole fraction of alcohol in the range 0-1%. An equilibriun~ constant for solvent nlolecule exchange has been deduced.Le radical cttyle est produit lorsqi~e des solutions de perfluorobenzophtnone sont photolystes avec de la lumiere ultraviolette. Le radical a pi1 Ctre identifit grice A la rtsonance de spin electroniqi~e inlpliquant des effets de solvant, de temptrature, d'echange chimique et de de~~teralion. Des melanges de solvant, cyclohexane-ethanol, ont conduit A des spectres ou I'on a denote ilne ires graude sensibilite vis-a-vis la fraction nlolaire d'alcool dans I'intervalle allant de 0-1%. De meme, on a dtduit ilne constante d'tquilibre pour I'tchange solvant-molecule.[Traduit par le journal]Can.

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