Monopolar compound

Figure 3.7 Plots of the natural logarithms of the air/surface partition constants, Kias, of a series of apolar and monopolar compounds for two different surfaces (i.e., teflon and quartz) versus the dispersive vdW-parameter of the compounds defined by Eq. 3-10. Note that from Eq. 3-10 only the compound part is used because the solvent part (1) is the same for all compounds, and that TSA, is in cm2 mol"1. (Data at 25 "C from Goss and Schwarzen-bach, 1998.)...

But let us now inspect the Yu values for the various chemicals given in Table 3.2. As we would probably have expected intuitively from our discussions in Section 3.2, Yu values close to 1 are found in those cases in which molecular interactions in the solution are nearly the same as in the pure liquid compound. For example, when the intermolecular interactions in a pure liquid are dominated by vdW interactions, and when solutions also exhibit only vdW interactions between the solute and solvent and between the solvent molecules themselves, we have Yu values close to 1. Examples include solutions of nonpolar and monopolar compounds in an apolar solvent (e.g., n-hexane, benzene, and diethylether in hexadecane), as well as solutions of nonpolar solutes in monopolar solvents (e.g., n-hexane in chloroform). In contrast, if we consider situations in which strong polar interactions are involved between the solute... 

A very different picture is found for the compounds in hexadecane. Here, the apolar and monopolar compounds show almost ideal behavior (i.e., Gj 0) because in their own liquids, as well as in hexadecane, they can undergo only vdW interactions. In the case of ethanol, again, a significant enthalpy cost and entropy gain is found, which can be explained with the same arguments used above for the gas phase. The absolute Hff and T-Sf( values are, however, smaller as compared to the gas phase, because ethanol undergoes vdW interactions with the hexadecane-solvent molecules, and because the freedom to move around in hexadecane is smaller than in the gas phase. 

Give at least three examples of environmentally relevant classes of (a) apolar, (b) monopolar, and (c) bipolar compounds. In the case of the monopolar compounds, indicate whether they are electron donors (H-acceptors) or electron acceptors (H-donors). 

Fig. 3.4 shows that when plotting the air-pure liquid compound partition constants of a large number of chemicals versus their dispersive vdW parameters, the apolar and monopolar compounds fall more or less on one line, while the bipolar compounds do not show this behavior. Explain these findings. For which kind of bulk liquids (give examples) would you expect that in a similar plot, all compounds (including the bipolar ones) should fit one line ... 

This expression reflects a weak relationship between the apolar or monopolar compound boiling temperature and entropy of vaporization, but substantially verifies Trouton s empirical observation. 

K values are equal to 1.0 for apolar and many monopolar compounds. For compounds exhibiting weakly bipolar character (e.g., esters, ketones, nitriles), a modest correction with a Kv of about 1.04 can be made. Significant corrections are necessary for primary amines (Kr = 1.10), phenols (KF = 1.15), and aliphatic alcohols (K = 1.30). For a more comprehensive compilation of Kv values, we refer to the literature (e.g., Grain, 1982a). 

Only for larger apolar and weakly monopolar compounds (e.g., PAHs, PCBs) are significantly more positive Hj values found. Indeed, if we examine the Hfw values within single compound classes, we can see that this parameter becomes more positive as the sizes ofthe structures increase (e.g., benzene, naphthalene, anthracene, benzo(a)pyrene). 

For monopolar compounds (e.g., ethers, ketones, aldehydes), Aaw//, may even be larger than A f/(.. This happens because of the additional polar interactions in the aqueous phase, leading to negative H%, values (Table 5.3). 

Figure 7.1 Plot of the decadic logarithms of the hexadecane-wa-ter partition constants versus the octanol-water constants for a variety of apolar, monopolar, and bipolar compounds. Data from Abraham (1994b). The a and b values for some LFERs (Eq. 7-7) are apolar and weakly monopolar compounds (a = 1.21, b = 0.43 Eq. 7-8), aliphatic carboxylic acids (a = 1.21, b = -2.88), and aliphatic alcohols (a = 1.12, b = -1.74).

For the following discussions, we will primarily use Kioc values from compilations published by Sabljic et al. (1995) and Poole and Poole (1999). According to these authors, the values should be representative for POM-water absorption (i.e., they have been derived from the linear part of the isotherms). Furthermore, many of the reported Kioc s are average values derived from data reported by different authors. Distinction between different sources of sorbents (e.g., soils, aquifer materials, freshwater, or marine sediments) has not been made. Nevertheless, at least for the apolar and weakly monopolar compounds, these values should be reasonably representative for partitioning to soil and sediment organic matter. 

We start out by considering the effect of such adsorption sites on the isotherms of apolar and weakly monopolar compounds. For these types of sorbates, hydrophobic organic surfaces and/or nanopores of carbonaceous materials are the most likely sites of adsorption. Such hydrophobic surfaces may be present due to the inclusion of particles like coal dust, soots, or highly metamorphosed organic matter (e.g., kerogen). Because of the highly planar aromatic surfaces of these particular materials, it is reasonable to assume that planar hydrophobic sorbates that can maximize the molecular contact with these surfaces should exhibit higher affinities, as compared to other nonplanar compounds of similar hydrophobicity. 

For compounds other than PAHs, unfortunately there are not enough data available that would allow a more general analysis of the concentration dependence of Kioc values. Nevertheless, a few additional observations may give us some better feeling of the magnitude of this dependence. For example, for sorption of smaller apolar and weakly monopolar compounds (e.g., benzene, chlorobenzene, 1,2-dichlorobenzene, tetrachloroethene, dibromoethane) to soil (Chiou and Kile, 1998) or aquifer materials (Xia and Ball, 1999 and 2000), not more than a factor of 2 difference in Kioc was found between low and high sorbate concentrations. A somewhat more pronounced effect (i.e., factor 2 to 3) was observed for sorption of the more polar... 

For example, such a relationship can be seen to apply to the data of Hutchinson et al. (1978), who reported the concentrations of numerous apolar and slightly monopolar compounds to inhibit microalgal photosynthesis by a factor of 2. When the effective concentrations (in mol L-1) are examined versus each compound s octanol-water partition coefficients, one finds the following relations ... 

Model for Energetics Controlling Air-Surface Adsorption of Apolar and Monopolar Compounds... 

Estimating Air-Surface Adsorption Coefficients of Apolar and Monopolar Compounds Applications... 

Partitioning of Apolar and Weakly Monopolar Compounds into the Region Near Mineral Surfaces... 

Before we discuss some applications of the polyparameter-LFER Eq. 11 -8, it is useful to have a short look at the surface parameters given for some important condensed phases in Table 11.1. Since the large majority of monopolar compounds are H-acceptors (i.e., at = 0, j8, 0), we focus our discussion primarily on the vdWsurf and HDsurf values. 

This means that for an apolar surface, all apolar or monopolar compounds should fit the same straight line. We have already demonstrated this for a teflon surface in Fig. 3.7 (note that the vdW parameter used in this graph is proportional to Pi, Eqs. 11-5 and 11-6). 

Figure 11.6 Sorption isotherms for two kinds of nonionic organic compounds from aqueous solutions to suspended kaolinite (a) slightly monopolar compound, pyrene, showing a linear isotherm up to its solubility (Backhus, 1990), and (b) monopolar compound, 1,3,5-trinitrobenzene, showing a hyperbolic isotherm (Had-erlein et al., 1996).

Some nonionic organic compounds exhibit much stronger mineral surface affinities than we see for apolar and weakly monopolar compounds like chlorobenzenes and PAHs. In these cases, the organic sorbates are able to displace water from the mineral surface and participate in fairly strong sorbate sorbent intermolecular interactions. Example compounds include mtroaromatic compounds (NACs) such as the explosive, trinitrotoluene (TNT), or the herbicide, 2,4-dinitro-6-methyl-phenol, also called dinitro-o-cresol (DNOC). 

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