Electron spin resonance studies. Part 58. The formation and reactions of some aliphatic radical-cations in aqueous solution

Abstract

Evidence is presented that reaction of C12-' with vinyl ethers proceeds via the formation of the radical-cations of the parent compounds. These species are not directly detectable by e.s.r., but the spectra of radicals formed in one or more of three further reactions have been characterized. These reactions are hydration, addition to the parent molecule, and deprotonation [e.g., CH,=CHOEt+' (from ethyl vinyl ether) yields the hydroxylated radicals*CH(OEt)-CH,OH and *CH,CH(OH)OEt and the ' dimer ' radical -CH(OEt)CH,CH,CH(OH)OEt].It has been confirmed that analogous radical-cations are also formed during the reactions of the hydroxyl radical with enol ethers at low pH and by elimination reactions of radicals of the type *CH(OR)CH,X (with X = CI, OH, or OMe). It is shown that furan is an effective spin trap for the radical-cations involved in these reactions.E.s.R. studies of the reactions of SO,-' with a variety of aromatic compounds have provided evidence that radical-cations are intermediates ; 2-5 in some cases (e.g. with methoxy-substituted benzoate anions) they are directly detectable.3 Radical-cations have also been proposed as key intermediates in the oxidation of aromatic compounds with, for example, the hydroxyl radical in acid solution,6 and, at least for electron-rich substrates such as p-methoxyphenol, with C1,-' .7 Although radicalcations have often been suggested as participating in the oxidation of aliphatic compounds [e.g. in the oxidation of some alkenes with SO,-' and in the acid-catalysed re-

Characterization of Free Radicals in Clathrate Hydrates of Furan, 2,3-Dihydrofuran, and 2,5-Dihydrofuran by Muon Spin Spectroscopy

“…The neat liquid sample gave similar results for A µ (see Table 1). Comparison with ESR data [38][39][40][41] and an earlier muon spectroscopic study 23 indicates that the stronger signal (smaller muon hfc) is due to radical 5 and the weaker signal is from 4. This assignment is supported by our DFT calculations, which show that 5 is more stable than 4, as might be expected from the enhanced spin delocalization over the allylic structure.…”

On the spin trapping of chlorine atoms. Competition from chloride ions

“…Gilbert et al (13) have reported formation of radical cations from the reaction of C12; with alkoxy-substituted olefins. In the current studies, an alternative mechanism leading to hydroxy spin adducts, involving nitrone radical cations (14) rather than intermediate chlorine spin adducts of PBN, cannot be ruled out.…”

Radical Cation, Dimer Radical Cation and Neutral Radical of 2,3‐Dihydropyran – Possible Initiators of its Polymerisation?

“…The spectrum of the DHP radical simulated with the set of hfs splitting constants given in Table 2 is shown in Figure 3(c). The same DHP radical was also generated chemically [22,23] and photochemically; [24] the experimental values of the hfs splitting constants are also summarized in Table 2.…”