Dipolar charge

He stressed the significance of measurements of molecular dipole moment, the principles of which had been established in 1912 by Debye.52 Ingold predicted that mesomeric systems would display measurable dipole effects. 53 He later said that he realized at this time that the theory of dipolar charge and intermediate form was... 

Unfortunately, the work function is a rather complicated (and not fully understood) function of the surface composition and geometry. The work function change is usually attributed to the formation of a dipole layer on the surface, such as occurs when charge flows from a substrate to an adsorbate, or vice versa. If a is the dipolar charge density, d the dipole length (perpendicular to the surface) and e the electronic charge, then one can write... 

Factors such as solvation and, in the case of ion-radicals, the counterion, may influence the properties of radicals. It is beyond the scope of this chapter to describe ion aggregation mechanisms and the factors which govern the hyperfine splittings manifested by counterions. The subject has been reviewed, however, by a prime mover in the field.12 Suffice it to say that the association of an ion-radical with a counterion may lead to a considerable redistribution of spin within the radical with consequences for the chemistry. For example, disproportionation equilibria and persistence may be influenced by the nature of the association.68 Closely allied to the phenomenon of ion association is, of course, solvation. Whether or not an ion-pair or other ionic assemblage exists in preference to free ions depends on the extent of the solvation of the ions. Nonionic radicals are also subject to variation in properties with change in solvent principally owing to interaction of the solvent with dipolar charges within the radical. 

Thus, as a first approximation, the water molecule can be represented as a dipolar charge distribution in which there is a positive charge of -Iq (due to the H atoms) at a distance a from the origin on the bisector of the H-O-H angle and a charge of -Iq (due to the lone electron pair) at a distance -fi from the origin it follows that... 

Indicators can exist as dipolar ions, and particularly at high ionic strength and in solvents of relatively low dielectric constant, each species is best regarded as consisting of n univalent anions, where n is the total charge including the dipolar charges." ... 

Water molecules have a unique dipolar structure that results in locally unsatisfied negative and positive charges associated with the oxygen atom and hydrogen atoms in the molecule (see Fig. 3.1). Because of this dipolar charge distribution, water molecules in contact with cations tend to be oriented with their oxygens toward the cation and their protons away from it, as shown schematically below for Ca-+ and a single water molecule. 

STILBAZOLIUM BASED DIPOLAR CHARGED ORGANIC COMPOUNDS... 

The outer potential is due to the free or excess charge on the surface of phase a and can be measured experimentally. The surface potential is due to the dipolar distribution of charge at the interface due to the unequal adsorption of ions and orientation of molecular dipoles. It cannot be measured experimentally. Since these quantities are defined with respect to the process of bringing a charged species from infinity into the phase, the surface potential is positive when the positive end of the dipolar charge points toward the center of the solution and the negative end toward charge-free infinity. 

Figure 2.2 a. Schematic representation of the possible orientation of charges in an ion-dipole interaction, (+) and (-) are ionic charges and (5+) and (5 ) are dipolar charges, b. Schematic representation of the possible orientation of charges in a dipole-dipole interaction. 

It is probably more like a dipolar charged ion, e.g. CaOH" (aq) or a charge-separated ion pair (Ca2+OH-)(aq). 

Other studies have shown conclusively that the species present at the first equivalence point is predominantly the dipolar, charge separated, or zwitterion, NH3CH2COO . 

These relaxation effects arise from orientation of dipolar charges created by the thermal decomposition reaction. 

Theory was compared with experimental results on ion—dipolar charge transfer [60, 61] and proton transfer [62, 63] reactions, and was found to predict very satisfactorily the rate coefficients of proton transfer reactions which are considered to proceed by a capture mechanism. The energy dependence of the proton transfer was also correctly represented by the theory. As to the charge transfer reactions, the comparison is difficult because the observed rate coefficients are considerably larger than the capture limit. This is explained by the contribution of a long range electron-jump mechanism to the rate coefficients. Even in this case, however, the trend of the dipole effect is predicted correctly by the theory. 

An externally applied electric field is a vectorial perturbation for chemical or orientational distributions involving interacting molecules or molecular organizations. Unlike the isotropic temperature and pressure effects on chemical-conformational transformations, direct sensitivity to electric field forces is bound to certain electrical properties of the chemical structures involved. Major structural-chemical changes in electric fields require the presence of ions, or ionized groups, or permanent or induced dipolar charge configurations, preferably in macromolecular structures. 

As there is globally no creation of electric charges (i.e., charge conservation), the sum of all charges is zero, which allows the dipolar charge to be equal to the polar charges and to the opposite of the other one, and to deduce the variation of dipolar charge... 

The fact that 3-hydroxypyrazoles are always predominant in the equilibria with their corresponding CH-tautomers is related to their aromaticity. Qualitative interpretations supported the hypothesis that the NH tautomer was less aromatic than the OH tautomer, and the CH tautomer was nonaromatic. Nuclear independent chemical shifts (NICS) values were calculated by using Schleyer s approach in order to determine the relative aromaticity of the pyrazole NH and OH tautomers using pyrrole as a reference. For pyrazole itself, the NICS value was close to pyrrole (—15.1 ppm). The NICS values were found to be —14.55 ppm for the 5-OH tautomer and —14.45 ppm for the 3-OH tautomer, indicating that the OH substituent does not alter the aromaticity of pyrazole and dipolar charges are not relevant. The NH tautomer has a NICS value of —6.75 ppm, intermediate between the OH tautomers and the nonaromatic CH tautomer, the latter with a NICS value of —0.25 ppm. 

A polar bond has a bond dipole moment equal to the product of the absolute value of the partial charge times the distance between the dipolar charges (the bond length). 

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