Direct Evidence for a Carbon–Carbon One‐Electron σ‐Bond, or a Weak Carbon–Carbon Interaction?

Shimajiri et al. ( Nature , 2024 , 634, 347–351) reported for the first time on direct evidence for a carbon–carbon one‐electron σ bond in a recently synthesized stable radical cation. Single‐crystal X‐ray diffraction analysis, electron density maps, and RAM spectroscopy provided analytical results supporting the derived picture. However, the theoretical counterpart at the density functional theory level tends to support a different viewpoint, namely two sp 2 carbon atoms at a rather high distance of 2.921(3) Å undergoing a weak non‐covalent interaction. In this contribution, we wish to highlight the discrepancies observed in relation to laboratory measurements as well as the similarities with a recent research by L. I. Lugo‐Fuentes ( Phys. Chem. Chem. Phys. , 2026 , 28, 683–691) with the aim of promoting new theoretical studies—going beyond the Kohn–Sham (KS) framework in the field of wavefunction correlated methods—on what could become a new benchmark system for the coming years. Taken together, the available data do not unequivocally demonstrate the existence of a discrete C─C one‐electron σ‐bond but instead highlight the difficulty of distinguishing extremely weak bonding interactions from non‐bonded or delocalized radical states.