How reliable is the hard–soft acid–base principle? An assessment from numerical simulations of electron transfer energies

Abstract

By computing the electron-transfer energies for two million simulated double acid–base exchange reactions, we assess the reliability of the global hard–soft acid–base (HSAB) principle. We find that the HSAB principle is often thwarted by the tendency of strong acids to prefer strong bases. We define the strong–weak and hard–soft driving forces to characterize the strength of these two competing effects, and assess the reliability of the HSAB principle for different strengths and directions of the hard–soft and strong–weak driving forces. We provide a series of probability tables for making informed predictions about the preferred products of double acid–base exchange reactions.