Molar attraction constant

Some molar attraction constants compiled by Small are given in Table 5.8. 

It is possible to calculate the solubility parameter and the solubility parameter components of almost all molecules and polymers by a group contribution method (Van Krevelen, 1990 Bicerano, 1996). For this purpose, as explained by Van Krevelen (1990) it is useful to introduce the molar attraction constant simply defined as ... 

To incorporate the surfactant structure concept, it is now convenient to introduce the group additive concept for cohesive energy densities (CED) introduced by Burrell and others (24, 25). Molecular segments are given a molar-attraction constant G. The CED is then determined for the ith compound as... 

Another aspect of this quasi-thermodynamic approach is to use Equation 25, along with G values from Table 4, to calculate the molar-attraction constant for the sodium sulfonate molecular group or... 

Beerbower equation and the additivity concepts of molar-attraction constants for determining the cohesive energy density. 

A direct measure of nonpolar character of a hydrocarbon molecule is given either by its molar solubility in water or by its molar attraction constant (Small s number) as given by Small... 

Because the heat of vaporization of a polymer is not readily obtained. Small determined values for various components of a polymer chain to calculate the solubility parameter. These values are called molar attraction constants and are additive and have been used for estimation of the solubility parameter for nonpolar polymers. In this approach 8 = D%G/M, where D is density, G are the Small molar attraction constants, and M is the molecular weight of the particular repeat unit. As expected, the more polar units have greater G values while the less polar units have smaller G values. 

G Gibbs free energy modulus molar attraction constant... 

THERMODYNAMICS OF CONDENSED PHASES Table 2.1 Molar Attraction Constants... 

Molar refractivity x ionization potential or molar refractivity alone, Hildebrand s molar attraction constant, or parachor... 

The 8 value of a polymer may also be calculated from Small s relationship, in which 2G is equal to the summation of the molar attraction constants of the individual repeating units constituting the polymer ... 

The alternative method is to calculate 8 for the polymer from the structural formula and the density of the polymer by using the molar attraction constants tabulated by Small (28). 

The molar attraction constants of dispersiS, dipole-dipole interactionsFpi hydrogen bonding,Ehi and the molar volume/ forthe drug and the hydrophobic block may be determined from group contribution tables provided by Hoftyzer-Van Krevelen and Fedor (Krevelen, 1990). 

Molar Attraction Constants F for Functional Groups of Chemical Compounds... 

Earlier, Small (1953) had demonstrated that the combination (Ecoh/V(298))1/2 = F, the molar attraction constant, is a useful additive quantity for low-molecular as well as for high-molecular substances. His set of values is very frequently applied. Accordingly, the corresponding solubility parameter is < smaii = F/V. Later Hoy (1970) proposed group contributions to F, slightly different from those of Small. 

The solubility parameter of a given material can be calculated either from the cohesive energy, or from the molar attraction constant F, as <5 = F/V... 

This means that for the prediction of <5d the same type of formula is used as Small proposed for the prediction of the total solubility parameter 8. The group contributions Fdi to the dispersion component Fd of the molar attraction constant can simply be added. 

In Eq. (12-13), (0 is the density of the amorphous polymer at the solution temperature, Mq is the formula weight of the repeating unit, and F, is the sum of all the molar attraction constants. A modified version of a compilation [4] of molar attraction constants is reproduced in Table 12-2. 

Fig. 12-1. Calculation of solubility parameters from molar attraction constants.

Other molecular properties have been also proposed to model the hydrophobic interactions. The parachor, which is related to the surface tension of a compound (139, 140) represents mainly the intermolecular interactions in a liquid. The Hildebrand-Scott solubility parameter, 6, (141) is related to intermolecular van der Waals forces and the closely related molar attraction constant, F, is obtained by multiplying 6 by the molar volume (142). The partition coefficient between two solvents can be obtained from the solubility parameters and the molar volumes of the solute and the solvents (193). This relationship is based on regular solution theory (194) and the assumption that the partial molar volumes of the solute is not different from its molar volume. Recently this has been criticized and a new derivation was proposed (195) in which the partial molar volumes are taken into account. The molar refractivity, MR, is related to dispersion forces and can be obtained as a sum of the partial molar refractivi-ties assigned to atoms and bonds (140, 143). These parameters have been compared (144) to establish their relative applicability to correlations with biological activity. The conclusion was that logP and molecular refractivity were the best parameters. Parameters obtained from high pressure liquid chromatography (144,... 

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