Gas-phase thermochemical properties of some tri-substituted phenols: A density functional theory study

• DFT calculations were performed for trisubstituted phenols.
• Enthalpies of formation for phenols and phenoxyl radicals were estimated.
• OH homolytic BDE, acidities and adiabatic ionization enthalpies were estimated.
• There is a general good agreement with the few existent experimental data.

The study of the energetics of phenolic compounds has a considerable practical interest since this family of compounds includes numerous synthetic and naturally occurring antioxidants. In this work, density functional theory (DFT) has been used to investigate gas-phase thermochemical properties of the following tri-substituted phenols: 2,4,6-trimethylphenol, 2,6-dimethyl-4-tert-butylphenol, 2,6-dimethyl-4-methoxyphenol, 2,4,6-tri-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-methoxyphenol, 2,4,6-trimethoxyphenol, 2,6-dimethoxy-4-methylphenol and 2,6-dimethoxy-4-tert-butylphenol. Molecular structures were computed with the B3LYP and the ωB97X-D functionals and the 6-31G(d) basis set. More accurate energies were obtained from single-point energy calculations with both functionals and the 6-311++G(2df,2pd) basis set. Standard enthalpies of formation of the phenolic molecules and phenoxyl radicals were derived using an appropriate homodesmotic reaction. The OH homolytic bond dissociation enthalpies, gas-phase acidities and adiabatic ionization enthalpies were also calculated. The general good agreement found between the calculated and the few existent experimental gas-phase thermochemical parameters gives confidence to the estimates concerning the phenolic compounds which were not yet experimentally studied.

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