APPRAISAL OF CHEMICAL-BOND MAKING, BOND BREAKING, AND ELECTRON-TRANSFER IN SOLUTION IN THE LIGHT OF THE PRINCIPLE OF MAXIMUM HARDNESS

Experimental heats of heterolysis (Delta H-het) and homolysis (Delta H-homo) and free energy changes Delta G(ET) associated with the electron transfer process are investigated theoretically for several series of compounds that have been produced by the direct reaction of resonance-stabilized carbenium ions with a variety of organic anions to produce C-C, C-N, C-O, and C-S bonds. Various empirical linear relationships show that the stabilities of molecules toward heterolysis can be analyzed in terms of the maximum hardness principle. The relationship between Delta H-het, Delta H-homo and Delta G(ET) for some symmetrical compounds, 9,9'-diphenylbixanthyl, bibenzyl, tetramethylbutane (bis-tert-butyl), and ethane, are established from published data which show the increasing strength of the central C-C bond in response to the stabilities of the cations, anions, and radicals produced by cleavage. The hypothetical pK(HA) of isobutane is discussed.