Systematic Testing of the Maximum Hardness and Minimum Electrophilicity Principles

By considering double-exchange reactions between 496 heteronuclear diatomic molecules composed of elements in the first four rows of the periodic table, we test the reliability of the principles of maximum hardness and minimum electrophilicity. Both principles are reasonably robust, especially for reactions that are decisively exothermic, but neither principle is perfectly reliable. Nevertheless, both principles provide good rules-of-thumb for chemical reactions. Removing reactions that violate the hard/soft acid/base rule from the data set enhances the reliability of the maximum hardness principle, offering support for the relationship between the maximum hardness and hard/soft acid/base principles. Both principles are reliable about 80% of the time if near-thermoneutral reactions are removed from the data set. For reactions that follow the hard/soft acid/base rule and that are strongly energetically favored, the maximum hardness principle predicts the correct products nearly 90% of the time.