Theoretical study of PhCH₂O₄CH₂Ph: intermediate in the PhCH₂O₂ self-reaction

As a possible important intermediate during the oxidation of toluene in gas phase, the PhCH₂O₄CH₂Ph molecule has been invested on the structural parameters at CAM-B3LYP/6-311+g(df,pd) level, the vibrational frequencies at B3LYP-D3(BJ)/6-311+g(df,pd) level, and the potential energy surface of isomerization between main isomers at CCSD(T)-F12/cc-pVDZ-F12 level of theory. Ten PhCH₂O₄CH₂Ph isomers were located, in which the structural parameters of C-O₄-C skeleton are close to those in HO₄H and C₂H₅O₄C₂H₅. However, due to larger steric hindrance of aromatic groups, PhCH₂O₄CH₂Ph has a more open geometry with larger bond angles and dihedral angles in individual isomers. Meanwhile, it seems that the hyperconjugation appears to be stronger between the O-O bonds and aromatic groups, since the O-O bond lengths are slightly shorter than those found in HO₄H and C₂H₅O₄C₂H₅. Harmonic vibrational frequencies of PhCH₂O₄CH₂Ph isomers were first reported here and we found that the frequencies of O₄ torsion and O-O/C-O stretches in PhCH₂O₄CH₂Ph are consistent with those of CH₃O₄CH₃ and C₂H₅O₄C₂H₅. In the progress of isomerization, three transition states were located and a thermodynamic equilibrium between three main isomers may achieve at ambient temperature concerning the characters of energy barrier.