Through electron transfer

One could envisage as a general mechanism for direct initiation the transfer of an electron from the monomer double bond to the Lewis acid  

A similar investigation from Szwarc s laboratory showed that 1,1-di-p-methoxy-phenylethylene can be transformed into its carbenium ion by reaction with an excess of antimony pentachloride. However, in this study it was postulated that the ionisation process involved the reduction of antimony throu one of the following alternative mechanisms  

This direct initiation process is certainly favoured by the very pronounced basicity of the oleftn used and moreover must be considered peculiar to antimony-based Lewis acids which combine a marked strength and the capacity of undergoing facile reduction. It is therefore a specific event which obviously does not explain the more general phenomenology of direct initiation in cationic polymerisation. 

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In addition to the above mechanism, the metal chelates can influence the process of quenching through electron-transfer ... 

Decay of donor-acceptor complex through electron transfer to solvent molecules yielding primary radical ion pairs ... 

In plants, the photosynthesis reaction takes place in specialized organelles termed chloroplasts. The chloroplasts are bounded in a two-membrane envelope with an additional third internal membrane called thylakoid membrane. This thylakoid membrane is a highly folded structure, which encloses a distinct compartment called thylakoid lumen. The chlorophyll found in chloroplasts is bound to the protein in the thylakoid membrane. The major photosensitive molecules in plants are the chlorophylls chlorophyll a and chlorophyll b. They are coupled through electron transfer chains to other molecules that act as electron carriers. Structures of chlorophyll a, chlorophyll b, and pheophytin a are shown in Figure 7.9. 

The Mechanism of Epoxide Opening through Electron Transfer ... 

Figure 3.11 Alkylation via radicals generated through electron transfer sensitization mechanism.

In other cases, the radical ion formed through electron transfer sensitization fragments (Figure 3.11). This is a new method for generating radicals from unconventional precursors under mild conditions. ... 

A range of examples of alkylation reactions via radicals generated through electron transfer sensitization is available in the literature, and a few of them are reported in Figure 3.12. Alkyl tin derivatives can be used as precursors, but in many cases these highly toxic reagents can be advantageously substituted by... 

Because of its high reduction potential of 2.43 V (see Table 6), it can be used to generate other strongly oxidizing radicals such as Cl and NOj through electron transfer reactions with Cl and N03, respectively [27]. 

The basic forms of phenols (phenolate anions) are easily oxidized to semiquinone radicals through electron transfer. These radicals can then react with another radical to form an adduct through radical coupling or, in the case of o-diphenols, undergo a second oxidation step yielding o-quinones that are electrophiles as well as oxidants. Oxidation reactions are very slow in wine, due to the low proportion of phenolate ions at wine pH values, but take place extremely rapidly when oxidative enzymes are involved (see Section 5.5.2.2). 

An excited state effectively quenched through electron transfer to or from redox... 

These potentials theoretically allow water photolysis. However, multi-electron processes have to occur at the catalyst in order to photolyze water with this complex. The lifetime of the excited state is 650 ns, and the excited state is quenched efficiently through electron transfer with redox reagents. The conversion model with this complex is described in Chapter 4. 

In the first reaction, it s obvious that electrons cire transferred from mc nesium to hydrogen. There are only two reactants, and magnesium is neutral as a reactant but positively charged as a product. The charges can change in this way only through electron transfer. 

Fig. 26. General reaction scheme for dye sensitized hole injection in organic crystals. The scheme shows the excitation of the adsorbed dye ( ... ) in the first row at the left hand side. Through electron transfer the "reduced dye-hole pair" (2D. . , 2C+) is generated with its singlet and triplet spin state (2. row). The dissociated "reduced dye-hole pair is shown in the third row, and finally the hole contributing to the injection current in the fourth row. The regeneration of the dye molecules can be seen on the left hand side of the third row and the generation of sensitized delayed crystal fluorescence in the first row on the right hand side. Details are explained in Section IV 4 of the text...

When the quencher contains heavy atoms nonradialive relaxation of the exciple occurs via the triplet state (heavy atom perturbation). A second mode of exciplex dissociation is through electron transfer between the excited molecule and the quencher. Ionization potential of the donor, electron affinity of the acceptor and solvent dielectric constant are important parameters in such cases. 

Since the efficiency of fluorescence quenching of the sensitizer paralleled the oxidizability of the arene in a series of substituted alkyl benzenes, the reaction was thought to proceed through electron transfer followed by protonation and trapping of the radical by oxygen. 

Titanium dioxide photocatalyzed oxidation of neat tetralin was previously reported to give its hydroperoxide (14). Reinvestigation showed that tetralol and tetralone are also formed in acetonitrile possibly through electron transfer from tetralin to the positive holes (27). 

A comprehensive picture at the molecular level has been developed for the titan-ocene-mediated epoxide ring opening through electron transfer. The investigations, carried out by experimental and computational techniques, have shown that the most reactive Ti(II) species is the dimer in its half-open structure and that the selectivity of the ring opening is governed by steric effects.393... 

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