Thermodynamics of Disproportionation and Heats of Hydration of 1,4-Benzosemiquinone and 1,4-Naphthosemiquinone at pH 7.1

Article abstract of DOI:10.1021/j100365a078

The thermodynamics of disproportionation of 1,4-benzosemiquinone (BQ^*-) and 1,4-naphthosemiquinone (NQ^*-) in cacodylic-cacodylate buffer at pH 7.1 was studied by spin resonance (ESR) spectroscopy and solution calorimetry.The disproportionation of BQ^*- was found to be more exergonic and exothermic than that corresponding to NQ^*- in both aqueous and gas phases.These semiquinones disproportionate about 40 times more exothermically in the gaseous than in the aqueous phase.The differences between the enthalpies of disproportionation corresponding to BQ^*- and NQ^*- are 51 and 14 kJ/mol in the gaseous and aqueous phases, respectively.The heats of hydration of BQ^*- and NQ^*- were determined with a convenient thermochemical cycle based on the enthalpies of disproportionation.The single-ion heats of hydration of BQ^*- and NQ^*- were found to be -360 and -377 kJ/mol, respectively.The heats of hydration of the net negative charge in BQ^*- and NQ^*- were found to be the same.