Hydrogen bonds complex permittivity

Dielectric measurements were used to evaluate the degrees of inter- and intramolecular hydrogen bonding in novolac resins.39 The frequency dependence of complex permittivity (s ) within a relaxation region can be described with a Havriliak and Negami function (HN function) ... 

Another factor influencing the reactivities of polar particles is their nonspecific solvation. Since both the individual particles, namely phenol and peroxyl radicals and their complex are polar, rate constants must depend on the polarity of the medium, its permittivity s, in particular. This was confirmed in experiments with mixtures of benzene and methylethyl-ketone, which showed that kq diminishes as the concentration of methylethylketone decreases provided the hydrogen bonding between the benzene and methylethylketone molecules are taken into account [10]. The dependence of ogkq on the medium permittivity s is described by the formula... 

A second limitation of the Hughes-Ingold theory concerns the fact that the solvent is treated as dielectric continuum, characterized by one of the following its relative permittivity, e, the dipole moment, fi, or by its electrostatic factor, EF, defined as the product of and [27]. The term solvent polarity refers then to the ability of a solvent to interact electrostatically with solute molecules. It should be remembered, however, that solvents can also interact with solute molecules through specific inter-molecular forces like hydrogen bonding or EPD/EPA complexation cf. Section 2.2). For example, specific solvation of anionic solutes by pro tic solvents may reduce their nucleophilic reactivity, whereas in dipolar aprotic solvents solvation of anions is less,... 

As the data for the Menschutkin reactions indicate, the character of the solute-solvent interactions is more complex than described by Eq. (5-87). It is evident that functions of relative permittivity alone, as given in Eq. (5-87), are not useful for describing the solvent effect on reactions between dipolar reactants, except in certain special cases, such as when a mixture of two solvents is used. In addition to electrostatic forces, non-electrostatic interactions, such as dispersion forces and hydrogen-bonding, must also be involved in Menschutkin reactions. 

The first mechanism (a) refers to dielectric relaxation pertinent to a permanent dipole influenced by a rather narrow hat intermolecular potential the next two (b, c) refer to the complex permittivity generated by two elastically vibrating hydrogen-bonded (HB) molecules. The last mechanism (d) refers to a nonrigid dipole vibrating in direction perpendicular to that of the undisturbed H-bond. 

We employ a classical description of the dynamical consequences of such a quantum object as the hydrogen bond. This concerns, for instance, the vibration of HB molecules. The price we pay for such an approach is that several fitted model parameters (e.g., force constants) are not related explicitly to the molecular structure of our object. Note that in the MD simulation method, based on application of various effective potentials, the classical theory is also often used [33-35]. Avery detailed analysis of the problems pertinent to the two-fractional (mixed) models of water is given in the latter work (review) with respect to various (mostly steady-state) properties of water. In the context of our work, the use of a classical mixed model is justified by a possibility of considering a simplified picture of two-state molecular motion allowing a relatively simple analytical calculation of the complex permittivity s(v) given in Section II. 

Ion-pair formation in the system. In systems containing complex cations, for example, the solvating effect and relative permittivity of the solvent control the extent of ion-pair formation between the complex cation and the associated anion similarly to the effect of hydrogen bond formation, this may lead to a change in, or the formation of, a dissymmetry centre,... 

Most BF3 affinities in Table 3.3 are primary values measured in dichloromethane. This solvent was chosen because it can dissolve most BF3 complexes, while being rather inert (low hydrogen-bond acidity, Lewis basicity and relative permittivity). Nitrobenzene also exhibits good solvent properties towards BF3 complexes, and some measurements were run on representative bases, in both C6H5NO2 and CH2CI2. A very good linear relationship was observed [5] between the enthalpy changes of reaction 3.4 in dichloromethane and nitrobenzene ... 

---