Interacting Quantum Atoms Analysis of Covalent and Collective Interactions in Single Elongated Carbon–Carbon Bonds

Chemical bonds among carbon atoms are central to chemistry. A general working principle regarding these interactions is that these contacts become stronger as the carbon atoms become closer to each other. Nevertheless, there are long, yet strong single C-C bonds that challenge this interpretation. Herein, we perform a quantitative thorough decomposition of the electronic energy of hexaphenylethane and several derivatives of this molecule with increasingly bulkier substituents. For this purpose, we exploit state-of-the-art methods of wave function analysis for the examination of the chemical bonding scenario in the examined systems, namely, the quantum theory of atoms in molecules (QTAIM) and the interacting quantum atoms (IQA) electronic energy partition. Our results reveal the predominance of collective non-covalent interactions over the central, covalent one in the chemical bonding of the examined molecules, in particular for those that have been synthesized in the laboratory. The QTAIM and IQA methods also showed that, besides London dispersion, electron sharing comprises an important contribution to the abovementioned collective interactions. Overall, our results give valuable insights about the importance of collective interactions in the investigated systems and they aid in the understanding of the nature of long, yet stable single C-C bonds.