Electron donation to

After its photooxidation, P-700 stays oxidized for more than a few microseconds. It is re-reduced by the soluble copper protein plastocyanin or, in cyanobacteria and some algae, by the soluble cytochrome c-553. The relationship between plastocyanin and P-700 has been mainly studied through kinetic analysis of the P-700 ab- 

The structure of plastocyanin is known at a highly refined level, which allows interesting hypotheses on which part of the molecule is involved in interactions permitting electron transfer [73]. Several areas on the surface of the molecule have been modified with chemical reagents, which can change the binding and reactivity [74], which are highly sensitive to electrical interactions, as shown by the influence of cations on the rate of electron transfer (see e.g. Refs. 68 and 75). 

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Figure 7-2 indicates that this intramolecular assistance takes place with those compounds having substituents to the right of X = OMe = —0.78), for in this portion of the a scale compounds 8 solvolyze more rapidly than do 7. At the X = OMe member, however, the two series have essentially identical reactivities, and this behavior continues at more negative cr. It. therefore, appears that intramolecular participation by the double bond occurs when it is needed when the X substituent is sufficiently electron-donating to stabilize the cation, intramolecular assistance is not needed, so it does not occur, and the saturated and unsaturated series show the same reactivity. 

Just the reverse trend characterizes fc2. This reaction is aided by electron donation to the carbonyl carbon, as would be expected if the mechanism consists of electrophilic addition of the proton to the OH group. The reaction constant is p = -1.74. 

Conversely, since increasing Uwr and coverage of O8 stabilizes the Rh-C2H4 bond via enhanced 7t-electron donation to the metal, it follows that smaller pc2H4 values (Pc2h4) are required to reduce the surface Rh oxide as experimentally observed. 

Electrons donated to the surface oxygen species are instantaneously replenished from the ohmic contact to maintain a steady state population of electron-filled (reduced) surface states determined by E cath-... 

Electron donation to nucleobases is a fundamental process exploited by nature to achieve the efficient repair of UV induced lesions in DNA [27, 28]. Nature developed to this end two enzymes, CPD photolyases and (6-4) photolyases, which both inject electrons into the UV damaged DNA bases [29, 30]. Both enzymes are, in many species, including plants, essential for the repair of the UV-light induced DNA lesions depicted in Scheme 1 [31]. 

Reversal of the expected (inductive) order of electron-donation to CH3>MeCH2>Me2CH>Me3C could be explained on the basis of... 

Albeit nitrile oxides are more regioselective than nitrones towards MCP, in cycloadditions with alkylidenecyclopropanes they show a lower regiocontrol than nitrones. The same trend, however, on passing from electron-donating to electron-withdrawing substituents is observed. Benzylidenecyclopropane (156) gives (entry 1, Table 28) only a 1 4 mixture (compared with 1 19 with nitrone... 

It provides appropriate electronic donation to the metal center... 

With these features in mind, we envisioned a new family of macrocyclic ligands for olefin polymerization catalysis (Fig. 9) [131, 132], We utilized macrocycles as the ligand framework and installed the catalytic metal center in the core of the macrocycles. Appropriate intra-annular binding sites are introduced into cyclophane framework that not only match the coordination geometry of a chosen metal but also provide the appropriate electronic donation to metal center. The cyclophane framework would provide a microenvironment to shield the catalytic center from all angles, but leaving two cis coordination sites open in the front one for monomer coordination and the other for the growing polymer chain. This could potentially protect the catalytic center and prevent it from decomposition or vulnerable side reactions. 

Spectator substituents, bonded to the carbene s migration terminus (Ci), directly influence the lifetime and philicity of the carbene, but they do not primarily alter the migratory aptitudes of migrants on C2. Oxa spectator substituents stabilize singlet carbenes by electron donation to the vacant carbenic p orbital (LUMO) cf. resonance hybrid 69. 

Chemically, it might be preferable to specify exactly the source of the electrons donated to form O2- ions in NiO. The physical properties of the solid suggest that the two electrons actually come from separate Ni2+ ions, converting each of them to the ion Ni3+. The defect is then a Ni3+ ion located on a Ni2+ site. This defect has an effective positive charge of one unit compared to the Ni2+ ion, so it would be written Ni. Taking this into account, the reaction Eq. (1.4) needs to be... 

The principal characteristic of the transition elements is an incomplete electronic subshell that confers specific properties on the metal concerned. Ligand systems may participate in coordination not only by electron donation to the 3d levels in the first transition series but also by donation to incomplete outer 4s and 4p shells. Figure 5.1 shows that the differences in orbital energy levels between the 4s, 4p and 3d orbitals are much smaller than, for example, the difference between the inner 2s and 2p levels. Consequently, transitions between the 4s, 4p and 3d levels can easily take place and coordination is readily achieved. The manner in which ligand groups are oriented in surrounding the central metal atom is determined by the number and energy levels of the electrons in the incomplete subshells. 

Ogliaruso et al. (1966) formed the ten 7r-electron monohomocycloocta-tetraene dianion [148]. In the same way that cyclooctatetraene dianion can be formed by donation of two electrons to cyclooctatetraene, their synthesis was the two-electron donation to the monomethylene adduct. H NMR studies support the assignment of the homoaromatic form [148] and exclude the classical form [149]. 

M60 octahedra (see Fig. 4.28). The solid-state structure results from the packing of such groups. The inter-cluster distances are similar to those found in the metals. According to Simon, these compounds could be described as ([Rb902]5+, 5e ) and ([Csh03]5+, 5e ) with the five electrons donated to a conduction band, both inter-and intra-cluster metal-metal bonding, in agreement with the metallic conductivity of these compounds. 

To understand what happens to the electron donated to the host, we have to consider the host s electronic structure. In transition metal chalco-genides or oxides, electron p orbitals from the chalcogen or oxygen overlap with s, p, and d orbitals from the transition metal, forming bonding and antibonding levels. The periodicity of the solid spreads... 

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