Intramolecular charge repulsion

The interaction and structure of PEs in a solvent (mostly water) are controlled to a large extent by electrostatic interactions [2, 15, 21]. In case of PEs in the strong dilution regime, this interaction leads to an intramolecular charge repulsion and to strongly extended, rod like chains [2]. For this reason the Bjerrum length. Is, which defines the distance at which the electrostatic interaction reaches the same value as the thermal energy ksT), is an important parameter [21] ... 

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... 

Deviations from this generalization may have several sources, including charge repulsion, steric effects, statistical factors, intramolecular hydrogen bonding, and other structural effects that alter electron density at the reaction site. Hague - ° P has discussed these effects. 

Takahashi et al.67) prepared ionene-tetrahydrofuran-ionene (ITI) triblock copolymers and investigated their surface activities. Surface tension-concentration curves for salt-free aqueous solutions of ITI showed that the critical micelle concentration (CMC) decreased with increasing mole fraction of tetrahydrofuran units in the copolymer. This behavior is due to an increase in hydrophobicity. The adsorbance and the thickness of the adsorbed layer for various ITI at the air-water interface were measured by ellipsometry. The adsorbance was also estimated from the Gibbs adsorption equation extended to aqueous polyelectrolyte solutions. The measured and calculated adsorbances were of the same order of magnitude. The thickness of the adsorbed layer was almost equal to the contour length of the ionene blocks. The intramolecular electrostatic repulsion between charged groups in the ionene blocks is probably responsible for the full extension of the... 

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. 

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