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The radical yields of C2H5' and CCI,' observed by electron spin resonance of CCI4 + C,H51 mixtures irradiated by y rays at 77 "K are compared with yields of HCI, I,, and HI measured after thawing. The dissociative capture of thermalized electrons by CC14 is extremely effective and accounts for most of the observed radicals. The difference between yields of HC1 and CCI3' results from charge transfer from C2H51' to CC1,'. The formation of iodine proceeds both from neutralization processes of C1-ions with positive ions formed from C2H51, and from ion-molecule reactions.On compare les rendements radicalaires observes par la resonance tlectronique paramagnttique aux rendements en HCI, I, et H I observes apris rkchauffement de melanges de CC14 et de C2H51 soumls aux irradiations des rayons y. La capture d'electrons thermalids est tris efficace dans le cas du CC14 et fournit la plus grande partie des radicaux observts. L'Ccart entre les rendements en HCI et CCI,' est dii au transfert de charge que subit C2H51+ avecCCI,'. Les reactions de neutralisation de C1-avec une entit6 positive issue de C2H51 et les reactions ion-molCcule sont a la base de la production d'iode. IntroductionIt has been shown that some y-irradiated halogenated alkanes form anions efficiently by electron capture, as indicated by the corresponding visible and U.V. spectra of the ionic species in organic glasses at -196 O C (1). In the same way, Hamill and his co-workers (1) have established a scale of relative efficiency of electron capture for a whole series of solutes dissolved in suitable solvents; these measurements were based on competitive reaction abilities of solutes for thermalized electrons produced within the medium; however, they were confined to low solute concentrations.It seems worthwhile to extend such a study over a wider range of concentration in a mixture of two solutes chosen from the Hamill scale. However, at high concentration the technique of measuring the optical spectrum of organic glasses at 77 OK does not give sufficient precision, therefore another experimental approach was preferred: the e.s.r. spectrum of radicals in frozen solutions and the subsequent chemical analysis of reaction products enabled us to establish a reaction scheme in such a system. In addition, irradiation in the solid phase has the advantage of limiting the reactions, especially of formed products, by preventing diffusion of bulky fragments in the solid.

Mixtures of ethyl iodide with chloroform, carbon tetrachloride, and dichloronlethane have been irradiated with 60Co y-radiation. Reduced yields of iodine, hydrogen iodide, and hydrogen chloride from ethyl iodide -chlorofornl and ethyl iodide -dichloromethane mixtures and of chlorinated ethanes from ethyl iodide -chloroforn~ are attributed to radical scavenging by iodine and dissociative electron capture by the chlorinated methane.Electron capture by carbon tetrachloride followed by ion-molecule reactions between ethyl iodide cations and ethyl iodide, or neutralization of these cations by chlorine anions, explains iodine yields observed at low ethyl iodide concentrations in carbon tetrachloride greater than those expected on the basis of partition of absorbed energy. In this mixture, neutralization of an ethyl iodide cation by a chlorine anion gives rise to an enhanced hydrogen chloride yield.

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1,3] and [3,3] Rearrangements of 3-Amino-1,5-hexadienes: Solvent Effect on the Regioselectivity.-3-Amino-1,5-hexadienes (I) rearrange in the presence of base to yield mixtures of cis,trans-isomeric [3,3] and [1,3] products (II), (III) and (IV). In some cases [cf. (V)] the regioselectivity is strongly influenced by the solvent.-(DOBSON, HEATHER K.; LEBLANC, RICHARD; PERRIER, HELENE; STEPHENSON, COREY; WELCH, TERESA R.; MACDONALD, DWIGHT; Tetrahedron Lett. 40 (1999) 16, 3119-3122; Merck Frosst Cent. Ther. Res., Pointe-Claire-Dorval, Que. H9R 4P8, Can.; EN)