Dipolarity-polarizability term

In the work of Famini and Wilson,a molecular volume, Vmc, (units of 100 A ) is used to model the cavity term that measures the energy required to create a solute-molecule sized cavity in the solvent. The dipolarity/polarizability term, which attempts to account for dispersion-type interactions, is modeled by the polarizability index, tij, (unitless). This index is defined as the average molecular polarizability divided by the molecular volume, a/Vmc, and helps account for the correlation between polarizability and molecular volume. 

Several QSRR studies have aimed at comparison of the retention mechanism on individual alkylsilica reversed-phase materials for HPLC employed the LSER-based analyte parameters. It was observed generally that the most important analyte parameters which influenced retention were bulkiness-related parameters (molar volume, molar refraction) and hydrogen-bonding basicity, but not hydrogen-bonding acidity. The analyte dipolarity/polarizability appeared a minor but often significant factor [96,97]. However, on polystyrene-divinylbenzene (PS-DVB) stationary pha.se the dipolarity/polarizability term provided an important positive input to the QSRR [981. 

Electric polarization, dipole moments and other related physical quantities, such as multipole moments and polarizabilities, constitute another group of both local and molecular descriptors, which can be defined either in terms of classical physics or quantum mechanics. They encode information about the charge distribution in molecules [Bbttcher et al, 1973]. They are particularly important in modelling solvation properties of compounds which depend on solute/solvent interactions and in fact are frequently used to represent the -> dipolarity/polarizability term in - linear solvation energy relationships. Moreover, they can be used to model the polar interactions which contribute to the determination of the -> lipophilicity of compounds. 

Y polarity scale -> linear solvation energy relationships (O dipolarity / polarizability term)... 

T = intercept + cavity term + dipolarity/polarizability term + hydrogen-bond term... 

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