Proton donor parameter

An alternative approach uses the polarity index, P proposed by Snyder. This is based upon experimentally determined gas chromatographic retention of three test solvents on a large number of stationary phases. The test solvents selected are ethanol, 1,4-dioxane and nitromethane. As well as an overall polarity index (P), three other parameters are calculated, Xe (a proton acceptor parameter), x[Pg.93]

Table 3 lists the Hildebrand solubility parameter 8, the total solubility parameter do, and the multicomponent parameters for dispersion dj, polar dp, and hydrogen bonding d/, forces for a number of solvents. These data are taken from the compilation by Barton (1975). He has pointed out that the data become empirical when multicomponent parameters are used, and thus it is important to use a set of data that are self-consistent. Keller et al. (1971) and Karger et al. (1976) have further subdivided the hydrogen bonding parameter into the acid or proton donor ( ) parameter, and the base or proton acceptor (6/,) parameter. Values for these are listed for some of the compounds in Table 3 from data provided by Snyder (1978). These data are not from the same source as those compiled by Barton (1975) and included in Table 3, and hence the values given for d/, should not be compared directly with those for 8 and 8. ... 

For example, nylon 66 will dissolve in formic acid, glacial acetic acid, phenol and cresol, four solvents which not only have similar solubility parameters but also are capable of acting as proton donors whilst the carbonyl groups on the nylon act as proton acceptors (Figure 5.6). 

The solubility parameter of poly(ethylene terephthalate) is about 21.8 MPa but because it is a highly crystalline material only proton donors that are capable of interaction with the ester groups are effective. A mixture of phenol and tetrachloroethane is often used when measuring molecular weights, which are about 20 000 in the case of commercial polymers. 

Note Solvent classification into groups based on solvent polarity selectivity parameters proton acceptor, proton donor, x dipole interactors) and solvent strength on alumina nd on silica gel 0. Physical constants viscosity (t)), surface tension (y), dielectric constant (8). Solvatochromic polarity parameters 7, j.(30) and Ej. ... 

We outline experimental results and provide theoretical interpretation of effect of adsorption of molecular oxygen and alkyl radicals in condensed media (water, proton-donor and aproton solvents) having different values of dielectric constant on electric conductivity of sensors. We have established that above parameter substantially affects the reversible changes of electric conductivity of a sensor in above media which are rigorously dependent on concentration of dissolved oxygen. 

The selectivity of a number of organic modifiers was examined using the predicted log k values of the log P — 3 models from each group in different organic modifier-water mixtures. The composition of the eluent was adjusted so that either the solubility parameter,1 polarity (Po), proton acceptor (Xa), proton donor (Xd), or dipole moment (Xn) values were kept constant to determine which parameter affected the selectivity. The results are summarized in Table 4.3. 

Among various physicochemical methods, IR spectroscopy and NMR are most appropriate tools for the study of dihydrogen bonds in solution. However, it is worth mentioning that these methods are basically different. First, they measure physical properties that change upon complexation bond vibrations and magnetic behavior. Second, equilibrium (4.1) is usually slow on the IR spectroscopy time scale and very fast on the NMR time scale. In other words, proton donors, proton acceptor, and their complexes are detected separately in IR spectra, whereas the NMR parameters of these moieties are usually averaged. 

TABLE 4.1. IR Spectral Parameters [v (OH) Regions] Obtained for Free and Dihydrogen-Bonded Proton Donors in CH2CI2 Solutions of the Ions [BioHio] " and [Bi2Hi2] ... 

Since the nature of the hydride chemical shifts, particularly in transition metal hydride complexes, is not simple [32], there is no reliable correlation between Sh and the enthalpy of dihydrogen bonding. Nevertheless, the chemical shifts of hydride resonances and their changes with temperature and the concentration of proton-donor components, for example, can be used to obtain the energy parameters for dihydrogen bonding in solution. As earlier, the enthalpy (A/f°) and entropy (AS°) values can be obtained on the basis of equilibrium constants determined at different temperatures. Let us demonstrate some examples of such determinations. 

Figure 8.2 shows a good linear correlation between the -AH° values and the H- H distances found for dihydrogen-bonded complexes formed by [A1H4] , [BH4] , [GaH4] , and Cp Fe(dhpe)H with different proton donors [5,7]. In this case the bonding energy increases from 5 kcal/mol to 12 kcal/mol and the H- -H distance changes between 1.3 and 1.7 A. It is probable that the linearity of this relationship is connected with the relatively narrow diapasons mentioned above. In fact, larger diapasons for both parameters lead to the polynomial dependence [12] shown in Figure 8.3. This pattern includes the dihydrogen-bonded complexes...

It was preferred to have one proton donor in the solvents. Chloroform (CHCI3) is the only solvent in Table 6.1 which is a proton donor. This is indicated by both the selectivity parameters and the solubility parameters. 

In this example, the relation between 19 chemicals and 23 physicochemical parameters was examined ( ). PLS, unlike canonical correlation, permits use of more chemical parameters than stimuli. The twenty-three physicochemical variables included molecular weight, functional groups, Raman frequencies and Laffort parameters (see ( )) The Laffort parameters are alpha (an apolar factor proportional to molvolume), rho (a proton receptor factor), epsilon (an electron factor) and pi (a proton donor factor). 

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