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Internet Electronic Journal of Molecular Design - IEJMD, ISSN 1538-6414, CODEN IEJMAT
| ABSTRACT - Internet Electron. J. Mol. Des. April 2003, Volume 2, Number 4, 262-273 |
Substituent Effects on O-H Proton Dissociation
Enthalpies of Catecholic Cation Radicals: A DFT Study
Hong-Yu Zhang, Xiu-Li Wang, and You-Min Sun
Internet Electron. J. Mol. Des. 2003, 2, 262-273
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Abstract:
Density functional theory (DFT) at the B3LYP/6-31G(d,p)
level was employed to investigate the
substituent effects on O-H proton dissociation enthalpies
(PDEs) of catecholic cation radicals. First, it was revealed
that the ortho OH-group had little influence on the O-H
PDE, because the electronic effect and the intramolecular
hydrogen bond (IHB) effect arising from ortho OH-group
counteract each other. Second, the 4-substituent effect
upon O-H PDEs for catecholic cation radicals was
comparable to that for monophenolic cation radicals,
which meant that electronic contributions played a
dominant role in the substituent effects. Third, there
existed good correlations between O-H PDEs and other
theoretical parameters, such as O-H bond length and
bond stretching frequency, suggesting these parameters
would be valid to characterize the proton dissociation
process, in contrast to the characterization of homolysis
of O-H bond that only bond dissociation enthalpy is an
appropriate parameter.
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