Valence bonds charge polarization

Chen, G., Lu. I).. Goddard, III. W.A. Valence-bond charge-transfer solvation model for nonlinear optical properties of organic molecules in polar solvents. J. Chem. Phys. 101, 5860-5864 (1994)... 

In valence bond terms the pyrazine ring may be represented as a resonance hybrid of a number of canonical structures (e.g. 1-4), with charge separated structures such as (3) contributing significantly, as evidenced by the polar character of the C=N bond in a number of reactions. The fusion of one or two benzene rings in quinoxaline (5) and phenazine (6) clearly increases the number of resonance structures which are available to these systems. 

In H202, there are a total of (2 x l) +(2 x 6) = 14 valence electrons, 7 electron pairs. The two O atoms are central atoms. A plausible Lewis structure has zero formal charge on each atom. H-0-0- H. In the hydrogen peroxide molecule, the O — O bond is non-polar, while the H — O bonds are polar, toward O. Since the molecule has a resultant dipole moment, it cannot be linear, for, if it were linear the two polar bonds would oppose each other and their polarities would cancel. 

The valence bond method with polarizable continuum model (VBPCM) method (55) includes solute—solvent interactions in the VB calculations. It uses the same continuum solvation model as the standard PCM model implemented in current ab initio quantum chemistry packages, where the solvent is represented as a homogeneous medium, characterized by a dielectric constant, and is polarizable by the charge distribution of the solute. The interaction between the solute charges and the polarized electric field of the solvent is taken into account through an interaction potential that is embedded in the... 

The most interesting feature of Fig.3 is the sharp peak in the weight of the metallic structures around 1.7 A. Each metallic structure has two polarized H2 molecules as a result of the transfer from a molecular valence bond to a new bond to a neighbor molecule (Fig.2). Our results therefore support a hypothesis, previously made [20], that the ground state wave function will have a component of charge-transfer states at pressures around 150 GPa. Moreover, our results indicate that small variations of the intermolecular separation around 1.7 A (as a result of a structural modification, for instance) can induce sizeable changes in the polarization of the H2 molecules. This is fully consistent with the spontaneous polarization predicted by Edwards and Ashcroft [21], and it provides an explanation for this phenomenon in terms of the chemical bonding in the solid. 

The analysis of the dipole moment curves for the motion of the adsorbate perpendicular to the surface provides additional information about the degree of ionicity of a given surface chemical bond. Moreover, the analysis of the dipole moment curves is also related to the interpretation of variations of the surface work function induced by the presence of the adsorbate. However, the response of the surface to the presence of the adsorbate does not permit to extract directly adsorbate charges from the dipole moment curve. A procedure based in the use of frozen densities has been proposed that permits to avoid the effect of the surface polarization on the dipole moment curve. Unfortunately, this method has not been yet extensively used. To close this short discussion about the different procedures commonly used to interpret the chemical bond between chemical species and the surface of a catalyst in terms of net charges we mention the valence bond reading of Hartree-Fock and Configuration Interaction wave functions. This procedure has been used to interpret the electronic correlation effect on the surface chemical bond. ... 

Fig. 3.21 Non-polar valence bond (at left) and zwitterionic full charge transfer (at right) forms of a donor-acceptor substituted polyene.

However, they pointed out that the sensitivity of J(Si-Q to the valence bond equivalent of PssiSc the compounds containing only Si, C, and H is substantially lower. (158) The authors suggest the possibility that this discrepancy arises from the assumption of a constant AE. Correlations with charge density parameters reflecting electron deficiency of the Si-C bond and polarization in the sense Si C are also found. (160)... 

The mechanism of electron transfer across a liquid-liquid interface is probably quite similar to that of a homogeneous electron transfer [106, 107]. In either case, the role of changes in the oxidation state of both reactants, in their molecular structure (including valence bond deformation, breaking or formation), and in the polarization state of the solvent have to be considered. Owing to electrostatic interactions of charged reactants with polar solvent molecules, the electron energy levels of the reac-... 

---