Molar polarizability distribution

The calculation of the molar polarizabilities, often involves statistical mechanical averaging over orientational distributions of the molecules. An important example is the distribution function w caused by dipole orientation in an externally applied static electric field E° because it describes the process of electric poling of NLO-phores. To second order in the field, the dipolar contributions to this (normalized) function are given by (100),... 

Bonding of solvent gas molecules to an activated surface generally involves co-alignment of charge distributions between the solvent and the activated site. The phrase molar polarizibility refers to the polarization of one mole of solvent. It is identified by the symbol Pe... 

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... 

Here, Vi is the molar volume of the solute (as a measure of the size of the cavity to accommodate the solute i in the solvent), d is an empirical parameter which takes also account for polarizability n, a and / characterize respectively the acidity or basicity which in general represents the ability to form hydrogen bonds, and the C s are solvent characteristics independent of the solute. Meyer and Maurer [39] used this equation for 30 systems (371 substances, 947 experimental distribution coefficients) to evaluate generalized solvent Cj parameters. 

Dispersion forces usually increase with molar mass. Molecules with larger molar mass tend to have more electrons, and dispersion forces increase in strength with the number of electrons because of increases in atomic or molecnlar polarizability. Furthermore, larger molar mass often means a bigger atom whose electron distribution is more easily disturbed because the outer electrons are less tightly held by the nuclei. Table 4.6 compares the melting points of similar substances that consist of nonpolar molecules. As expected, the melting point increases as the number of electrons in the molecule increases. Becanse these are all nonpolar molecules, the only attractive inter-molecular forces present are the dispersion forces. 

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