Alkanes, volume distribution

The solvent triangle classification method of Snyder Is the most cosDBon approach to solvent characterization used by chromatographers (510,517). The solvent polarity index, P, and solvent selectivity factors, X), which characterize the relative importemce of orientation and proton donor/acceptor interactions to the total polarity, were based on Rohrscbneider s compilation of experimental gas-liquid distribution constants for a number of test solutes in 75 common, volatile solvents. Snyder chose the solutes nitromethane, ethanol and dloxane as probes for a solvent s capacity for orientation, proton acceptor and proton donor capacity, respectively. The influence of solute molecular size, solute/solvent dispersion interactions, and solute/solvent induction interactions as a result of solvent polarizability were subtracted from the experimental distribution constants first multiplying the experimental distribution constant by the solvent molar volume and thm referencing this quantity to the value calculated for a hypothetical n-alkane with a molar volume identical to the test solute. Each value was then corrected empirically to give a value of zero for the polar distribution constant of the test solutes for saturated hydrocarbon solvents. These residual, values were supposed to arise from inductive and... 

FIGURE 15.3. Distribution data between water and sodium dodecyl sulfate micelles as a function of the solute McGowan volume for the entire database (a) and for categorized classes of solutes (b), data from Reference 25. Database labels in (a) as in Figure 15.2. (A) hexadecane-water partition data for alkanes, from Reference 16. Labels in (b) ( ) alkyl benzenes (O) alkyl phenyl ketones (A) alkyl phenols ( ) halo benzenes and ( ) halo phenols. 

The distribution can be changed, however, by using different gas-water ratios. Table I shows the partitioning of various classes of hydrocarbons for selected gas-water ratios. Increasing the gas-water ratio partitions a higher percentage of the individual hydrocarbons to the gas phase. However, the concentration per unit volume of gas decreases with increase in gas-water ratios for n-alkanes, alkenes, and cycloalkanes. Aromatic hydrocarbons, by coincidence, partition to give approximately the same concentration per unit volume of gas over gas-water ratios from 1 10 to 10 1. 

Stress-strain isotherms have also been calculated with this approach. Examples are unimodal networks of polyethylene and POMS, " polymeric sulfur and seleniirm, short n-alkane chains, natural rubber, several polyoxides, and elastin, and bimodal networks of PDMS. It is possible to include excluded volume effects, in such simulations. In the case of the partially helical polymer polyoxymethylene, the simulations were used to resolve the overall distributions into contributions from imbroken rods, once-broken rods, twice-broken rods, and so on. It was also shown how applying stresses to the ends of chains of this typ>e can be used to bias the distributions in the direction of increased helical content and increased average end-to-end distances. In this sense, imposition of a stress has the same effect on the helix-coil equilibriirm as a decrease in temperature. ... 

McAuliffe (15) introduced a multiple-phase equilibrium procedure for the qualitative separation of hydrocarbons fi om water-soluble organic compounds. For n-alkanes, more than 99% was found to partition in the gas phase after two equilibriums with equal volumes of gas and aqueous solution. Cycloalkanes require three equilibriums to be essentially completely removed, and oxygen-containing organic compounds (e.g., alcohols, aldehydes, ketones, and acids) remain in the aqueous layer. After equilibrium with equal volumes of gas, an immediate clue is given regarding the identification of the compound. More details of this technique can be found in Chapter 11. This technique also provides two additional pieces of information the distribution coefficient (Dg or Dg) and the initial concentration of the unknown component. 

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