2.5- Dihydrofuryl radical

Transformations of the radical cations of 2,3- and 2,5-dihydrofuran (DHF), radi-olytically generated in Freon matrices, were investigated by low-temperature EPR. The 2,3-DHF+ radical cation is stable at 77 K but at higher temperatures is transformed into dihydrofuryl radical, DHF. The oxygen-centred radical cation 2,5-DHF+ is unstable at 77 K and transforms via an intramolecular H-shift into a transient distonic radical cation 2,4-DHF+ which at higher temperatures yields the DHF radical. 

Once formed, the dihydrofuryl radicals may undergo a variety of reactions as known from homogeneous chemistry including disproportionation, addition to double bonds, electron transfer and dimerization. Surprisingly, the latter pathway is followed to about 90 % as indicated by the complete material balance [145]. It is therefore likely that C-C coupling occurs between radicals within the water-2,5-DHF surface layer. This is corroborated by the quadratic dependence of the initial... 

In summary, one can conclude that the formation of H2 and the dehydrodimer occurs via subsequent adsorption of two photons (2e"/2h process). The intermediately adsorbed hydrogen atom and dihydrofuryl radical generated by the first photon must have lifetimes long enough to wait for the arrival of the second photon. This requirement is easily fulfilled since at a micrometer-sized ZnS particle the time interval between two successive photon absorptions can be estimated to be in range of 20 ps, much shorter than the lifetime of radicals and radical cations which... 

The mechanism of the photodehydrodimerisation of 2,5-dihydrofuran on suspended ZnS powders has been investigated using a variety of techniques. Both mono- and multilayer adsorption participate, and the substrate appears to be adsorbed perpendicularly to the surface at all of the available zinc sites. Dissociative electron transfer occurs from the adsorbed substrate to a reactive hole affording a proton and a dihydrofuryl radical. 

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