Hydrogen bonds 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) ... 

It has been pointed out321-324 that the two groups of solvents differ by some definite structural features. In particular, ED, 1,2-BD, and 1,3-BD possess vicinal OH groups that can form intramolecular hydrogen bonds. For these solvents, the ability of the organic molecule to interact with neighboring molecules is reduced. This results in the possibility of a different orientation at the interface because of different interactions of the OH groups with the Hg surface.323 The different molecular structure leads to different dipolar cooperative effects. As a result, the dependence of C on the bulk permittivity follows two different linear dependencies. 

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... 

Permittivity measurements have been used to study hydrogen bonding of phenol or carboxylic acids with trialkylphosphine oxides (154). The results can be explained in terms of a simple electrostatic model. The properties of trimethylphosphine oxide were different from the general properties of the series.189... 

The problem of influence of the electric field intensity on the permittivity of solvents has been discussed in many papers. The high permittivity of water results from the intermolecular forces and is a cumulative property. The electric field intensity is the lowest at the potential of zero charge (pzc), thus allowing water molecules to adsorb in clusters. When the electrode is polarized, the associated molecules, linked with hydrogen bonds, can dissociate due to a change in the energy of their interaction with the electrode. Moreover, the orientation of water molecules may also change when the potential is switched from one side of the pzc to the otha. 

When the relative permittivity of the organic solvent or solvent mixture is e < 10, then ionic dissociation can generally be entirely neglected, and potential electrolytes behave as if they were nonelectrolytes. This is most clearly demonstrated experimentally by the negligible electrical conductivity of the solution, which is about as small as that of the pure organic solvent. The interactions between solute and solvent in such solutions have been discussed in section 2.3, and the concern here is with solute-solute interactions only. These take place mainly by dipole-dipole interactions, hydrogen bonding, or adduct formation. 

Liquid polyols are interesting among nonaqueous solvents because, like water and monoalcohols, they are hydrogen-bonded liquids with a high value of relative permittivity (Table 9.2.1), and therefore they are able to dissolve to some extent ionic inorganic compounds. Moreover, reactions can be carried out in such solvents under atmospheric pressure up to 250°C, i.e., at a temperature range higher than in water or monoalcohols such as methanol or ethanol. 

Some other classification schemes are provided in a work by Kolthoff (Kolthoff, 1974). It is according to the polarity and is described by the relative permittivity (dielectric constant) e, the dipole moment p (in 10 ° C.m), and the hydrogen-bond donation ability Another suggested classification (Parker, 1969) stresses the acidity and basicity (relative to water) of the solvents. A third one (Chastrette, 1979), stresses the hydrogen-bonding and electron-pair donation abilities, the polarity, and the extent of self-association. A fourth is a chemical constitution scheme (Riddick et al., 1986). The differences among these schemes are mainly semantic ones and are of no real consequence. Marcus presents these clearly (Marcus, 1998). 

In hydrogen-bonded ferroelectrics, the Curie temperature and permittivity alter when deuterium is substituted for hydrogen. What does this suggest about the origin of the ferroelectric transition in these compounds ... 

Hydrogen bonding in liquid water was discussed. The significance of the dipolar character of the water molecule was pointed out and its relation to the large value of the permittivity of the bulk... 

The solvents used for electroanalytical determinations vary widely in their physical properties liquid ranges (e.g., acetamide, N-methyl-acetamide and sulfolane are liquid only above ambient temperatures), vapour pressures (Table 3.1), relative permittivities (Table 3.5), viscosities (Table 3.9), and chemical properties, such as electron pair and hydrogen bond donicities (Table 4.3), dissolving ability of the required supporting electrolyte to provide adequate conductivity, and electrochemical potential windows (Table 4.8). A suitable solvent can therefore generally be found among them that fits the electroanalytical problem to be solved. 

In the applications of the PCM approach to SD, the focus so far has been mainly on the comparison with experiment [45,46] and very good agreement with experimental results has been obtained for C153 in several polar liquids [45], In the case of SD in water, the theory was implemented using two different approaches to obtain e(w), either a fit to experimental data [45] or a calculation of the dipole density time correlation from molecular dynamics simulation [46], While the results for S(t) that use experimental dielectric permittivity as input look quite similar to those shown in Figure 3.16, the results based on the simulation data exhibit more pronounced oscillatory features at the characteristic frequency of the hydrogen bond librations. 

In 1975 Mauret et al. (75BSF1675) carried out a detailed dipolarimetric study of the azole series, on the basis of the various, and sometimes conflicting, values of the dipolar moments reported in the literature. For pyrazole and imidazole, measurements were performed with the solvents dioxane and benzene at different concentrations and at 25°C, with the aim of determining the influence of concentration and solvent on the value of the dipolar moments, and, at the same time, the involvement of the different molecular associations owing to the formation of intermolecular hydrogen bonds. Thus, for imidazole (linear polymers), the dipolar moment increased with a rise in concentration, whereas for pyrazole (cyclic dimers), the dipolar moment decreased with higher concentrations, and consequently the dielectric permittivity fell. 

Another environmentally benign solvent is supercritical water, which has a great potential to replace conventional solvents, although it requires rather harsh experimental conditions tc = 374 °C and Pc = 218 atm see Table 3-4) [224, 225]. At the critical point of SC-H2O, its volume is three times larger than that at ambient temperature, its relative permittivity is only 5.3 (compared to e, = 78.4 at 25 °C), and its intermolecular hydrogen-bond network is partially broken. Under supercritical conditions, water consists of small clusters, oHgomers, and even monomeric gas-like water molecules [226,... 

An apolar aprotic solvent is characterized by a low relative permittivity (sr < 15), a low dipole moment [ju < 8.3 10 Cm = 2.5 D), a low value ca. 0.0... 0.3) cf. Table A-1, Appendix), and the inability to act as a hydrogen-bond donor. Such solvents interact only slightly with the solute since only the non-specific directional, induction, and dispersion forces can operate. To this group belong aliphatic and aromatic hydrocarbons, their halogen derivatives, tertiary amines, and carbon disulfide. 

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