Intramolecular coulombic repulsion

Ding C F, Wang X B and Wang L S 1998 Photoelectron spectroscopy of doubly charged anions intramolecular Coulomb repulsion and solvent stabilization J. Phys. Chem. A 102 8633... 

Ion radicals play a role as mediators in these two-electron transfers. Each one-electron step achieves a maximal rate, and both rate constants become close. Coulombic repulsion of positive (or negative) charges makes the double-charged ion formation difficult. Therefore, donors (or acceptors) are preferable for which some possibility exists to disperse the charge. Extension of the 77-system reduces intramolecular coulombic repulsion in the dianion state. Electron-donor (or electron-acceptor) substituents should be located at diametrically opposite sites of the molecule. Examples are ll,ll,12,12-tetracyano-9, 10-an-thraquinodimethane, TCNQ, DCNQI, and tetracyanobenzene. 

The delocalization of positive charges in the dication of TTF (see below, TTF2+) is extended to two outer double bonds, and therefore the intramolecular coulombic repulsion is smaller than in the dication of tetrahydro-II F (222+). As a result, a higher value of log K for 22 has been observed, and although the first oxidation of 22 takes place at a higher potential, its cation radical is thermodynamically more stable than that of TTF. 

An interesting trend in the variation of donor ability of these compounds can be observed upon replacing the sulfur atoms in TTF molecule by heavier selenium or tellurium atoms. Whereas the replacement of sulfur by selenium gives rise to an increase in the oxidation potentials, tetratel-lurafulvalene (TTeF) oxidizes more easily than the tetraselena analog (TSF). The value of log K increases in the series TTeF < TSF < TTF, indicating that there is an increase in intramolecular coulombic repulsion (Table 8). 

In contrast to this, the scaling theory of the PE star collapse developed in [27] suggested that, instead of the formation of a collapsed core, a decrease in the solvent strength may provoke the formation of bundles by the sticking of individual branches to each other. The bundle formation reduces the excess interfacial free energy of the collapsed domains, without a significant penalty in terms of the intramolecular Coulomb repulsion. More recently, the formation of bundles was theoretically predicted in colloidal PE brushes [42]. 

Although the CV data indicate that these 7t-extended DCNQI derivatives are slightly poorer electron acceptors than DCNQI, the smaller difference between the midpoint potentials for the first and second reductions, compared with that for the parent DCNQI, suggest a reduction of the intramolecular Coulomb repulsion due to the rr-system extension. 

C.-F. Ding, X.-B. Wang, and L.-S. Wang,/. Phys. Chem. A, 102, 8633-8636 (1998). Photoelectron Spectroscopy of Doubly Charged Anions Intramolecular Coulomb Repulsion and Solvent Stabilization. 

The key to understand the anomalous behaviors in A vC,o is the electron-electron interaction, U, and the electron-phonon interaction, S. In A vCgo, the important interaction as U is the Coulomb repulsion between the flu electrons. The importance of U has been pointed out based on the results of the photoemission experiments [15]. Also, in AxC o, the important interaction as S is the coupling of the tlu electrons to the intramolecular phonons of the CRaman experiments [16], Nevertheless, a complete understanding of the anomalous behaviors in AxCgo has not been established yet. The reason is that the system with the orbital degree of freedom in which both U and S are important has not been known so far [17-20],... 

In this section, a model which gives the basis of the present study is introduced to investigate the electronic properties of A,Cfio [17]. First, the one-electron part of the Hamiltonian, which describes the itinerant motion of the flu electrons in terms of the electron transfer T, is given. Next, the electron-electron interaction U and the electron-phonon interaction S are examined U represents the Coulomb repulsion between the t u electrons and S represents the coupling of the fiu electrons to the intramolecular phonons of the Cdynamical aspect of S is pointed out. 

The nonlinear branched topology is expected to introduce novel specific features in the collapse transition of individual charged macromolecules, due to the interplay between intra- and interbranch Coulomb repulsion. Conformations of intrinsically hydrophobic star-branched PE have been studied experimentally in the past decade [50, 51]. Recently synthesized PDMAEMA stars responsive to both pH and temperature [47, 48] are expected to undergo an intramolecular collapse transition as a response to the increase in temperature. The latter provokes a decrease in the solubility of the monomers in the star arms. 

Fig. 33.3 Forces and relaxation dynamics of the segmented 0 H-0 bond. Asymmetric and coupling relaxation dynamics of the master-slave-segmented 0 H-0 bond in water ice under applied stimulus. Short-range interactions of intramolecular H-O bond exchange interaction, intermolecular 0 H non-bond vdW interaction (broken red lines), interelectron-pair Coulomb repulsion (broken white lines), forces of Coulomb repulsion /q, deformation recoveryand the force driving relaxation acting on the electron pairs (small dots). H atom is the coordinate origin. Because of the strength disparity, Mi] > lAdnl the Coulomb repulsion makes the Adg and the A l shift in the same direction by different amounts (Reprinted with permission from [14])...

Ultrashort-range interactions of inter-electron-pair Coulomb repulsion, inter-molecular van der Waals force, and intramolecular exchange form the key to the unusually asymmetric relaxation in length and stiffness of the 0 H-0 bond and therefore anomalies of water ice in response to cooling, clustering, and squeezing. 

A key to both methods is the force field that is used,65 or more precisely, the inter- and possibly intramolecular potentials, from which can be obtained the forces acting upon the particles and the total energy of the system. An elementary level is to take only solute-solvent intermolecular interactions into account. These are typically viewed as being electrostatic and dispersion/exchange-repulsion (sometimes denoted van der Waals) they are represented by Coulombic and (frequently) Lennard-Jones expressions ... 

The bonding of ions to metals is dominated by Coulomb attraction since there is a significant difference in electron affinity between the metals and ions. The bonding also involves a redistribution of charge through intermolecular charge transfer (between adsorbed ions and the surface) and intramolecular polarization (in ions and on the surface), which reduces the Pauli repulsion. 

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