ADDITIVITY METHODS IN MOLECULAR POLARIZABILITY

Empirical methods to calculate average molecular polarizabilities based on atomic hybrid parameters are reexamined. New sets of optimized atomic hybrid components, rA(ahc), and atomic hybrid polarizabilities, aA(ahp), are presented. They yield average molecular polarizabilities with complementary empirical formulas, α(ahc) = (4/N)[ΣAτA(ahc)]2 (N = number of electrons in the molecule) and α(ahp) = ΣAτA(ahp), which reproduce the experimental polarizabilities to an average error of 2.2% and 2.8% respectively for approximately 400 compounds containing H, C, N, O, S, F, CI, B, I, and P. Only one parameter, τA or αA, in each formula is required for each atom, A, in a particular atomic hybridization state. Conjugate parameters, αA*(ahp) = (4/NA)τA(ahc)2 and τA*(ahp) = [NAαA(ahp)/4]1/2 (NA = number of electrons in atom A) used as alternate sets in these two empirical formulas, yield average molecular polarizabilities to a root-mean-square standard deviation of 5.6% and 6.4%, respectively. These two partitioning schemes are discussed. The atomic hybrid polarizabilities can be combined to generate bond polarizabilities, bp and two possible sets are discussed. In addition, the atomic polarizabilities are related to group polarizabilities, gp. The atomic hybrid methods require fewer parameters than the bond or group polarizability methods, but the ahc, ahp, bp, and gp methods yield comparable results. © 1990, American Chemical Society. All rights reserved.