Structure, thermochemistry, and conformational analysis of peroxides ROOR and hydroperoxides ROOH (R = Me, But, CF3)

The equilibrium structures, total energies, and harmonic frequencies of peroxides ROOR and ROOH (R = Me, Bu^t, CF₃) were calculated using the perturbation theory (MP4//MP2 method) and density functional approach (B3LYP) in the 6-31G(d,p) basis set. The conformational flexibility of peroxides under rotation about the O-O bond was investigated. It was found that the stable conformation of a peroxide molecule is determined by superposition of the destabilizing effects (repulsion between the lone electron pairs, steric hindrances) and the interaction of the nonbonding orbitals of oxygen atoms with the antibonding orbitals of the adjacent polar bonds. The latter effect stabilizes the nonplanar structure of the peroxide molecule. The role of orbital interactions in manifestation of the d-effect (distortion of the tetrahedral configuration of the X₃CO fragment of peroxide molecule) was revealed. The vibrational spectra of peroxides were calculated and compared with the experimental data. The potential energy distribution over normal vibrations was analyzed. The enthalpies of formation and the bond strengths in the molecules of compounds examined were calculated in the framework of the isodesmic reaction approach.