ISSN:
0020-7608
Keywords:
Computational Chemistry and Molecular Modeling
;
Atomic, Molecular and Optical Physics
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The stepwise acid dissociation constants for p-benzohydroquinone (QH2) in aqueous media have been explicitly calculated for the first time, with the INDO parametrized SCF-MO method. We have optimized the geometries of QH2, QH-, and Q2- and of the QH2 · 6H2O, QH- · (H3O+) · 5H2O, and Q2- · (H3O+)2 · 4H2O systems that model the solvated species. The presence of the associated water molecules (and hydronium ions) account for the stabilization due to hydrogen bonding as well as for a part of the effect of interaction of these molecules with the respective reaction fields in an aqueous medium. To simulate the first solvation shell in a more complete manner, four more water molecules have been considered to be placed above and below the quinonoid ring and the optimized geometries of the resulting hydrated species, QH2 · 10H2O, QH- · (H3O+) · 9H2O, and QH- · (H3O+) · 8H2O, have been determined. The standard free-energy changes calculated for the dissociation of QH2 into QH- and H+ is 0.0251 Hartree (65.9 kJ mol-1) and that of QH- into Q2- and H+ is 0.0285 Hartree (74.8 kJ mol-1). Experimentally observed dissociation constants for these two steps correspond to free-energy changes of 0.0214 Hartree (56.2 kJ mol-1) and 0.0248 Hartree (65.1 kJ mol-1), respectively. © 1995 John Wiley & Sons, Inc.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/qua.560530107
