RELATIONSHIPS BETWEEN THE AQUEOUS ACIDITIES OF SOME CARBON, OXYGEN, AND NITROGEN ACIDS AND THE CALCULATED SURFACE LOCAL IONIZATION ENERGIES OF THEIR CONJUGATE BASES

Average local ionization energies (IBAR(r)) have been computed on the molecular surfaces of the conjugate bases for four different groups of carbon and oxygen acids using an ab initio self-consistent-field molecular orbital approach. The lowest surface IBAR(r) (IBAR(S,min)) are generally found on the atom from which the proton has been abstracted. Good linear relationships between aqueous acidities and IBAR(S,min) are found for the different groups. A single linear relationship between pK(a) and IBAR(S,min) that includes the four groups and three additional nitrogen acids also exists; the correlation coefficient is 0.97. This provides a means for predicting the pK(a)'s of a large variety of carbon, oxygen, and nitrogen acids.