Alkyl radical traps

It has subsequently been shown (Maeda et ai, 1978) that the rates of these alkyl-radical trapping reactions show no significant solvent dependence. 

ESR spectra of irradiated alkylhalides were studied by Smaller and Matheson (21), and Ahscough and Thomson(22). They observed alkyl radicals trapped in the alkylhalide glasses. Claridge and Willard... 

The results demonstrate the value of being able to select the matrix independently of the radical precursor. The e.s.r. spectra of alkyl radicals trapped in their parent hydrocarbon or halohydrocarbon are often poorly resolved, and only the major hyperfine splitting constants can be determined. By using a bulky hydrocarbon such as camphane or adamantane as a matrix a marked increase in resolution has been observed for the spectra of many alkyl radicals up to Ce and all of the cyclo-alkyl radicals up to Cy. As an example, the spectra of the cyclohexyl radical trapped in matrices of cyclohexane and camphane are shown in Fig. 7. In cyclohexane the a and major )3-proton hyperfine splittings are not well resolved, and the small )3 splitting is not observed at all, whereas in camphane all three hyperfine splittings are readily observed. 

For an alkyl radical trap in aqueous medium see Barton, D.H.R. Jacob, M. Peralez, E. Tetrahedron Lett. 1999, 40, 9201. 

Oxidations Using Fe(III) Salts (Fenton Reaction) in Aqueous Media Fenton Chemistry is Yet Another Example of a Novel and Efficient Alkyl Radical Trap in Aqueous Medium... 

Macro-alkyl radicals trapped in the crystalline domains. 

Open-ring nitroso- [224] 144 and nitrocompounds [126] 145 were reported as the ultimate products of ROO reaction with HAS derived nitroxides. A-Oxide 146 was mentioned among the ultimate products of HAS as well [225]. Some alkyl radical trapping and 102 quenching activities should be preserved in 146. 

Fig. 7.15 Decay curves of alkyl radicals trapped in y-irradiated PE single crystals Circles, experimental solid curve. calculated. The figure is adapted from [15] with permission from Elsevier...

An answer to the question posed above can be found in the following study of free radicals trapped in a urea-polyethylene complex (UPEC). Figure 7.7 in Section 7.4.1 showed ESR spectra observed at 320 K which demonstrated the difference between the spectra of the alkyl radicals trapped in UPEC and those in solution grown crystals. The conclusion was that the radical sites in the UPEC were more mobile than in the crystals. The difference between the decay behavior of the alkyl radicals trapped in the complex and in the solution grown crystals is shown in Fig. 7.16. It can be said that the free radicals in the complex have a very long life time at 318 K and the decay rate in the complex at 411 K is of the same order as that in... 

In general, alkyl radicals trapped in polymer materials convert to peroxy radicals when oxygen molecules are introduced. The disappearance of the double quintet due to the chain type fluoro alkyl radicals in polytetrafluoroethylene (PTFE) described... 

Fig. 4.3. The decay curve of alkyl radicals trapped in irradiated single crystals of polyethylene A-85 at 269 K after heating at 195 K for a long time. ESR observations were made at 77 K ( ) Plot of raw data without any reduction, (O) plot of reduced amount after subtracting the amount of nonvanishing radical species. Solid line shows calculated decay curve with A = 4x 10 sec and B = lxlO sec (Ref.

The materials were y-irradiated up to ca. 1 Mrad at 77 K at about 10" Pa, and the ESR spectra of the alkyl radicals trapped in the polyethylene chain of the respective materials were recorded. The temperature dependence of hyperfine splitting due to p protons will mainly be discussed based on McConnell s relation (Eq. (2.2)). After... 

The motional narrowing of the line width obtained from the spectrum of broad-line proton NMR of d-UPEC and the motional narrowing of the line width from the ESR spectrum of alkyl radicals trapped in polyethylene chains in UPEC were analyzed based on the method described in the preceding section. 

Another recently introduced group of alkyl radical trapping agents is the benzo-furanone derivatives (Pitteloud and Dubs, 1994) ... 

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