Conventional analyses of indirect nuclear spin–spin coupling (SSC or J-coupling) in molecular systems typically focus on propagation through the framework of formal covalent bonds. However, in systems featuring functional groups in close proximity but separated by multiple covalent bonds, measurable through-space (TS) coupling can occur. Different mechanisms of TS coupling are commonly distinguished by the types of orbitals dominating them (e.g. lone-pair orbitals) or the type of non-covalent interaction keeping the coupling moieties in close proximity (e.g. hydrogen bonds). This article investigates the significance of the propagation of coupling specifically through \(\pi \) -orbitals. Using a novel approach for the evaluation of direct and indirect contributions of \(\pi \) -orbitals to SSC in the framework of non-hybrid density functional theory (DFT), we analyse the role of \(\pi \) -orbitals in TS coupling across small molecular gaps between two \(\pi \) -orbital containing moieties. Therein, we make special use of Komorovský’s version of the spin-spin coupling constant density to confirm the TS character, and of Malkina’s approach to the "indirect" \(\pi \) -orbital contribution to SSC via the transfer of spin polarisation ( \(\pi \) -TSP effect) to evaluate the \(\pi \) -character of the investigated SSCs. Our results demonstrate that measurable C–C TS SSC between \(\pi \) -carbons can occur. However, \(\pi \) -orbitals, beyond their structural role in enabling close proximity between the coupling moieties via \(\pi \) – \(\pi \) stacking interactions and CH \(\cdots \pi \) hydrogen bonds, appear to play only a minor role in the TS transfer of SSC between those moieties.
