INDEX electron transfer

Electron Level Position. One essential condition of spectral sensitization by electron transfer is that the LUMO of the dye be positioned above the bottom of the conduction band, eg, > —3.23 eV in AgBr or > —4.25 eV in ZnO (108). To provide the desired frontier level position respectively to the valence and conduction bands of the semiconductor, it is necessary to use a polymethine with suitable electron-donor abiHty (Pq. Increasing the parameter (Pq leads to the frontier level shift up, and vice versa. Chain lengthening is known to be accompanied by a decrease of LUMO energy and hence by a decrease of sensitization properties. As a result, it is necessary to use dyes with high electron-donor abiHty for sensitization in the near-ir. The desired value of (Pq can be provided by end groups with the needed topological index Oq or suitable substituents (112). 

Cumulative Subject Index Single electron transfer reactions... 

The electron affinity of the carbocations as measured by red is a useful index for the stability of the carbocations. It is of great interest to correlate the occurrence of three principal reactions between a carbocation and a carbanion, i.e. covalent bond formation (36), single-electron transfer (37) and salt formation (38), with the magnitude of the E ed for the carbocations. 

The degree of polymerization depends on the duration of the process. After 7 min, the molecular mass is equal to 9400 (the polydispersity index is 5.30). When the reaction is carried out for 15 min, the molecular mass of the polymer increases to 37,000 and the polydispersity index reaches 7.31 (Bauld et al. 1996). Depending on whether cation-radical centers arise at the expense of intramolecular electron transfer or in a stepwise intermolecular lengthening, polymerization can occur, respectively, through a chain or a step-growth process (Bauld and Roh 2002). In the reaction depicted in Scheme 7.17, both chain and step-growth propagations are involved. 

CONTENTS Acknowledgments, Margery G. Ord and Lloyd A. Stocken. Introduction. Biochemistry Before 1900. Early Metabolic Studies Energy Needs and the Composition of the Diet. Carbohydrate Utilization Glycolysis and Related Activities. Aspects of Carbohydrate Oxidation, Electron Transfer, and Oxidative Phosphorylation. Amino Acid Catabolism in Animals. The Utilization of Fatty Acids. The Impact of Isotopes 1925-1965. Biochemistry and the Cell. Concepts of protein Structure and Function. Chronological Summary of Main Events Up to ca. 1960. Principal Metabolic Pathways. Index. 

Although the usual way of analyzing the influence of the kinetics of the electron transfer on the SWV response is based on the variation of the frequency at fixed values of the staircase and square wave amplitude, a new approach for carrying out this analysis has been proposed based on the study of the influence of the square wave amplitude sw on the current potential curves at a fixed value of the frequency (or the time pulse) [19, 33, 34], The square wave amplitude has been used rarely as a tool in mechanistic and kinetic studies. One of the main reason is that, as stated in Sect. 7.1, in SWV the current is plotted versus an index potential which is an average potential between the forward and reverse potentials (see Eq. (7.7)) and leads to a discrepancy between the plotted and actual potentials at which the current is sampled. Therefore, the role played by Esw in the process is complex. 

The three curves shown in Fig. 3 are the ones calculated by using this Hamiltonian. Here, f J1 is the electronic transfer T between the fiu orbital a of the mth C60 molecule and the fiu orbital b of the nth C o molecule, where a and b denote x, y, and z f is chosen so as to reproduce the result of the electronic structure calculations. We also use spin electron in the flu orbital a of the mth C60 molecule. Furthermore, is the band energy of the flu electron of the band index a (a = 1,2, and 3) and the wavenumber k the band energies are obtained by diagonalizing the Hamiltonian H0 and we use ak(J(akli) to denote the corresponding creation (annihilation) operators. 

MO studies of aromatic nitration cast doubt on the existence of jt-complexes and electron-transfer complexes in liquid-phase nitrations.14 The enthalpy of protonation of aromatic substrates provides a very good index of substrate reactivity to nitration. Coulomb interaction between electrophile and substituent can be a special factor influencing regioselectivity. A detailed DFT study of the reaction of toluene with the nitronium ion has been reported.15 Calculated IR spectra for the Wheland intermediates suggest a classical SE2 mechanism. MO calculations of cationic localization energies for the interaction of monosubstituted benzenes with the nitronium ion correlate with observed product yields.16... 

Structure 9 is not very likely because, by electron transfer it would lead to structures having a negative charge on carbons 2 and 5. As we shall see, this is incorrect, the charge on these atoms being clearly positive. In The Ring Index, 6 compound 10 is named [l,2]dithiolo-... 

Maintaining constancy of n implies that s"(r, r ) is an electron-transfer reactivity index. In contrast to BP, who assumed implicitly that the definition of Eq. (66) was meaningful for all systems at all temperatures, we restricted in [3] consideration of the softness kernel to gapless systems for the reasons presented in Sect. 4. As a consequence, we were able in [3] to obtain from Eq. (66) an explicit form for s"(r, r ) via the Kohn-Sham equations,... 

Comparison of these calculated exciton transitions with the experimental data in Table V shows that the main features of the results are reproduced. The energies for the <100) surface (5-coordinated ions) are only slightly shifted from the bulk, whereas those transitions corresponding to the higher index planes are much closer to the experimental data. On an atomic scale this means that ions whose coordination numbers are 4 and 3 are involved in the observed transitions, whereas 5-coordinated ions at the surface will absorb at higher energies closer to the bulk band edge. This theoretical treatment is approximate since it considers only an ideal surface and assumes that the electron affinity and ionization potential are constant for the different planes. In fact, the evidence already presented on electron transfer in Section VI,A indicates that the ionization potential varies with the coordination of the ion. 

Figure 2.7. Dependence of the logarithm of relative parameters of the exchange interaction on the distance between the interacting centers (AR). krr is the rate constant of triplet-triplet electron transfer, and JSE is the spin-exchange integral. Index 0 is related to van der Waals contact. (Likhtenshtein, 1996) Reproduced in permission.

The second contribution, AG out, is the energy involved in reorganization of the solvent shell prior to electron transfer. This part of the activation energy is calculated by treating the solvent as a dielectric continuum with refractive index n and a static dielectric constant Db-Moreover, the two reactants are commonly approximated by spheres of radii and 03. If the distance r between the centers of the two redox partners in the activated complex is assumed to be equal to the sum of 02 and 03, then,... 

I. 3 A and the electron transfer distance is 3.5 A. The optical (square of the refractive index) and static dielectric constants of the solvent were used. 

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