Electron-donor-acceptor complex mechanism

Three main mechanisms have been proposed to explain this behavior the TT-TT dispersion interaction mechanism, the H-bonding formation mechanism, and the electron donor—acceptor complex mechanism. The first two mechanisms were proposed by Coughlin and Ezra [16] in 1968, and the third mechanism was proposed by Mattson and coworkers [20] in 1969. At that time, phenol was known to be adsorbed in a flat position on the graphene layers, and in this situation the adsorption driving forces would be due to tt-tt dispersion interactions between the aromatic ring of phenol and the aromatic structure of the graphene layers. 

Three mechanisms have been proposed to explain this behavior, namely (a) the TT-TT-dispersion interaction mechanism, (b) the hydrogen-bond formation mechanism and (c) the electron-donor-acceptor complex mechanism. To give these ideas a historical... 

Electrochemistry, organic, structure and mechanism in, 12, 1 Electrode processes, physical parameters for the control of, 10, 155 Electron donor-acceptor complexes, electron transfer in the thermal and photochemical activation of, in organic and organometallic reactions. 29, 185 Electron spin resonance, identification of organic free radicals, 1, 284 Electron spin resonance, studies of short-lived organic radicals, 5, 23 Electron storage and transfer in organic redox systems with multiple electrophores, 28, 1 Electron transfer, 35, 117... 

The Patterno-Buchi coupling of various stilbenes (S) with chloroanil (Q) to yield fran -oxetanes is achieved by the specific charge-transfer photo-activation of the electron donor-acceptor complexes (SQ). Time-resolved spectroscopy revealed the (singlet) ion-radical pair[S+% Q" ] to be the primary reaction intermediate and established the electron-transfer pathway for this Patterno-Buchi transformation. Carbonyl quinone activation leads to the same oxetane products with identical isomer ratios. Thus, an analogous mechanism is applied which includes an initial transfer quenching of the photo-activated (triplet) quinone acceptor by the stilbene donors resulting in triplet ion-radical pairs. ... 

Recently, Kochi et al. described a novel photochemical synthesis for a-nitration of ketones via enol silyl ethers. Despite the already well-known classical methods, this one uses the photochemical excitation of the intermolecular electron-donor-acceptor complexes between enol silyl ethers and tetranitrometh-ane. In addition to high yields of nitration products, the authors also provided new insights into the mechanism on this nitration reaction via time-resolved spectroscopy, thus providing, for instance, an explanation of the disparate behavior of a- and (3-tetralone enol silyl ethers [75], In contrast to the more reactive cross-conjugated a-isomer, the radical cation of (3-tetralone enol silyl ether is stabilized owing to extensive Tr-delocalization (Scheme 50). 

Figure 1. Distinct approaches to the template synthesis of molecules with mechanical bonds ionic coordination complex I, ionic electron donor-acceptor complex II and neutral complex III with hydrogen bonds.

Electrochemistry, organic, structure and mechanism in, 12, 1 Electrode processes, physical parameters for the control of, 10, 155 Electron donor-acceptor complexes, electron transfer in the thermal and... 

As an alternative to the classical mechanism shown in Scheme 29, a multi-step mechanism involving an electron donor-acceptor complex and a radical pair is shown in Scheme 30122. The distinction between the two mechanisms is difficult to make122-125. They can compete in forming the reaction products the idea that only one reaction pathway is operating, is an oversimplification. However, two relevant points cannot be disregarded ... 

They acknowledge that the exact mechanism of the adsorption of heavy metal chelates is quite complex but do not hesitate to propo.se the formation of an electron donor-acceptor complex of the chelate and the active sites (e.g., carbonyl groups) and possible beneficial effect of hydrogen bonding between the... 

It was accordingly demonstrated that the formation of electron donor-acceptor complexes is associated with the appearance of new catalytic activity and the further extension of the concept of electron donor-acceptor would possibly lead to a fuller insight into the mechanism of heterogeneous catalysis. 

Mattson and coworkers suggested that aromatic compounds adsorb on carbons by a donor-acceptor complex mechanism, with the carbonyl oxygen of the carbon surface acting as the electron donor and the aromatic ring of the adsorbate acting as the acceptor. Once the carbonyl groups are exhausted, the... 

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