LAUSR

The quantum theory of atoms‐in‐molecules (QTAIM) method is used to examine the OO bond in peroxides (RO‐OR) and nitroxide dimers (R2NO‐ONR2), including Fremy's salt. The electron density (ρ), electron kinetic energy density [K(ρ)], and Laplacian of the electron density (∇2ρ) at bond critical points characterize the nature of the OO bond. The data distinguish OO bonding of two kinds. Large values of ρ and positive ∇2ρ and K(ρ) suggest that simple peroxides have charge‐shift bonds. Nitroxide dimers, with smaller ρ, positive ∇2ρ, and near‐zero K(ρ), show a lack of shared electron density, suggesting there is no conventional OO bonding in these molecules. QTAIM analysis at the B3LYP/6–311+G(d,p) level of theory gives results in agreement with valence‐bond theory and X‐ray diffraction characterizations of peroxide OO bonds as charge‐shift bonds. In contrast, CCSD/cc‐pVDZ calculations fail to agree with previous results because of an insufficient, single‐determinant treatment of the charge‐shift bond.