Premium
Theoretical calculation of electrode potentials: Electron‐withdrawing compounds
Author(s) -
Lister Simon G.,
Reynolds Christopher A.,
Richards W. Graham
Publication year - 1992
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560410206
Subject(s) - ab initio , chemistry , basis set , molecule , electrode potential , standard electrode potential , electrode , perturbation theory (quantum mechanics) , ab initio quantum chemistry methods , electron , computational chemistry , electrostatics , atomic physics , thermodynamics , molecular physics , physics , electrochemistry , quantum mechanics , density functional theory , organic chemistry
Abstract The electrode potential of 2,3‐dicyanobenzoquinone in aqueous solution has been calculated relative to parabenzoquinone using a thermodynamic cycle approach that includes accurate gasphase ab initio calculations and calculation of differences in free energies of hydration using the free‐energy perturbation method. The discrepancy between the calculated and experimental electrode potential is disappointingly large (99 mV) compared to previous studies using this approach. This, along with the experimental evidence, suggests that the experimental value itself is too large and that theoretical approaches may indeed be as reliable as experimental ones for determining redox properties of molecules such as 2,3‐dicyanobenzoquinone. In the light of this discrepancy we have examined the variation of the results with the basis set, inclusion of electron correlation and changes in the parameters used in the molecular dynamics free‐energy simulations. The results are shown to be dependent upon the torsional parameters and especially dependent upon the basis set or semiempirical method used to obtain the electrostatic potential‐derived charges. The best charge set was determined using the ab initio criteria of completeness—as far as it can be applied to large molecules—and also by studying the effect of hydration on these charges. This was done by allowing the solvent to perturb the wave function prior to the electrostatic potential determination. Thus, 3‐21 G and 6‐31 G * basis sets were found to give satisfactory results. Similar results were obtained using semiempirical and ab initio geometries.