| Abstract
| - The electronic effects on O−H proton dissociationenergies (PDEs) of para- and meta-substituted phenoliccation radicals have been investigated by density functionaltheory (DFT) using B3LYP function on a 6-31G(d, p) basisset. The calculation results indicate that electron-donatinggroups raise the O−H PDE and electron-withdrawing groupsreduce the parameter, which are opposite to the electroniceffects on O−H bond dissociation energies (BDEs). Inaddition, the electronic effects on O−H PDE are muchstronger than those on O−H BDE. The differences resultfrom the distinct electronic effects on stabilities of phenoliccation radicals and parent phenols. The finding also impliesthe proton-transfer process is unlikely a rate-controlling stepfor phenolic antioxidants to scavenge free radicals. Moreover,like O−H BDE, O−H PDE correlate better with the resonance parameter R+ than with field/inductive parameter F.Therefore, O−H PDEs of para-substituted phenolic cationradicals are mainly governed by the resonance effect.
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