PDF(Sci-hub)
Abstract：
This article dwells on the nature of \"inverted bonds\", which refer to the σ interaction between two sp hybrids by their smaller lobes, and their presence in [1.1.1]propellane. Firstly, we study H3 C-C models of C-C bonds with frozen H-C-C angles reproducing the constraints of various degrees of \"inversion\". Secondly, the molecular orbital (MO) properties of [1.1.1]propellane and [1.1.1]bicyclopentane are analyzed with the help of orbital forces as a criterion of bonding/antibonding character and as a basis to evaluate bond energies. Triplet and cationic states of [1.1.1]propellane species are also considered to confirm the bonding/antibonding character of MOs in the parent molecule. These approaches show an essentially non-bonding character of the σ central C-C interaction in propellane. Within the MO theory, this bonding is thus only due to π-type MOs (also called \"banana\" MOs or \"bridge\" MOs) and its total energy is evaluated to approximately 50 kcal mol-1 . In bicyclopentane, despite a strong σ-type repulsion, a weak bonding (15-20 kcal mol-1 ) exists between both central C-C bonds, also due to π-type interactions, though no bond is present in the Lewis structure. Overall, the so-called \"inverted\" bond, as resulting from a σ overlap of the two sp hybrids by their smaller lobes, appears highly questionable.
摘要：
暂无翻译
