Modified Interaction Properties Function for the Analysis and Prediction of Lewis Basicities

Ab initio HF/6-31G* electrostatic potentials and average local ionization energies have been computed for 42 nitrogen, oxygen, and sulfur bases. The molecules are characterized by four computed quantities, Vmin, the spatial minimum in the electrostatic potential, PVmin, a polarization correction to Vmin, ĪS,min, the surface minimum in the average local ionization energy, and Π, a global index derived from the calculated surface electrostatic potential. It is shown that shifts in the O−H stretching frequencies for methanol−base complexes, complexation enthalpies for phenol−base and iodine−base interactions, and gas phase protonation enthalpies can be well correlated to the computed quantities of the bases by a single type of relationship. An analysis of the importance of the different quantities for correlating a specific interaction provides information about the nature of the interaction.