DFT/B3LYP study of O-H bond dissociation enthalpies of para and meta substituted phenols: Correlation with the phenolic C-O bond length

In this paper, the study of phenol and 30 compounds representing various para- and meta-substituted phenols is presented. Molecules and their radical structures were studied using DFT/B3LYP method in order to calculate the O-H bond dissociation enthalpies (BDEs). Calculated BDEs were compared with available experimental data. BDE values approximated from the total electronic energies are in very good agreement with data from solution measurements. Calculated gas-phase BDEs are lower than BDEs approximated from the total electronic energies about 26-30 kJ mol−1 and this difference does not depend on the substituent. DFT describes the effect of substituents on BDE satisfactorily, though ΔBDEs are in slightly narrower range than experimental values. Dependence of BDE values on Hammett constants of the substituents is linear. We found, that instead of phenolic O-H bond properties, BDE can be successfully correlated with the neighboring C-O bond length or with its shortening after hydrogen atom abstraction. In the case of substituents in para position, BDE linearly depends on the partial charge on phenolic group oxygen, too.