Currently, bonding analysis of molecules based on the Quantum Theory of Atoms in Molecules (QTAIM) is popular; however, "misinterpretations" of the QTAIM analysis are also very frequent. In this contribution the chemical relevance of the bond path as one of the key topological entities emerging from the QTAIM's topological analysis of the one-electron density is reconsidered. The role of nuclear vibrations on the topological analysis is investigated demonstrating that the bond paths are not indicators of chemical bonds. Also, it is argued that the detection of the bond paths is not necessary for the "interaction" to be present between two atoms in a molecule. The conceptual disentanglement of chemical bonds/interactions from the bonds paths, which are alternatively termed "line paths" in this contribution, dismisses many superficial inconsistencies. Such inconsistencies emerge from the presence/absence of the line paths in places of a molecule in which chemical intuition or alternative bonding analysis does not support the presence/absence of a chemical bond. Moreover, computational QTAIM studies have been performed on some "problematic" molecules, which were considered previously by other authors, and the role of nuclear vibrations on presence/absence of the line paths is studied demonstrating that a bonding pattern consistent with other theoretical schemes appears after a careful QTAIM analysis and a new "interpretation" of data is performed.

Quantum chemical calculations using density functional theory and correlated ab initio methods of the 10 π‐electron systems (N6H6)2+ and C2N4H6 show that the planar forms are no minima on the potential energy surfaces. The twisted ring structures of the two species are energy minima, but acyclic isomers are much lower in energy. The planar geometries sustain strong diamagnetic ring current comparable with that of benzene. In contrast, the calculated multicenter normalized Giambiagi electron delocalization index ING suggests that π‐delocalization in planar (N6H6)2+ and C2N4H6 is much weaker than in benzene. Since aromaticity is synonymous for a particular stability of cyclic delocalized systems, it may be stated that calculation or measurement of magnetic chemical shifts due to induced ring currents is not a reliable method to ascertain the aromatic character of a molecule. Aromatic compounds exhibit ring current induced magnetic shielding, but the reverse conclusion that ring current induced magnetic shielding identifies aromaticity is not justified. Furthermore, the 4n+2 rule as indicator of aromatic stabilization should only be used in conjunction with the ring size; the nature of the occupied π orbitals must always be examined.

The significant role of relativistic effects in altering the NMR chemical shifts of light nuclei in heavy-element compounds has been recognized for a long time; however, full understanding of this phenomenon in relation to the electronic structure has not been achieved. In this study, the recently observed qualitative differences between the platinum and gold compounds in the magnitude and the sign of spin-orbit-induced (SO) nuclear magnetic shielding at the vicinal light atom ((13)C, (15)N), σ(SO)(LA), are explained by the contractions of 6s and 6p atomic orbitals in Au complexes, originating in the larger Au nuclear charge and stronger scalar relativistic effects in gold complexes. This leads to the chemical activation of metal 6s and 6p atomic orbitals in Au complexes and their larger participation in bonding with the ligand, which modulates the propagation of metal-induced SO effects on the NMR signal of the LA via the Spin-Orbit/Fermi Contact (SO/FC) mechanism. The magnitude of the σ(SO)(LA) in these square-planar complexes can be understood on the basis of a balance between various metal-based 5d → 5d* and 6p → 6p* orbital magnetic couplings. The large and positive σ(SO)(LA) in platinum complexes is dominated by the shielding platinum-based 5d → 5d* magnetic couplings, whereas small or negative σ(SO)(LA) in gold complexes is related to the deshielding contribution of the gold-based 6p → 6p* magnetic couplings. Further, it is demonstrated that σ(SO)(LA) correlates quantitatively with the extent of M-LA electron sharing that is the covalence of the M-LA bond (characterized by the QTAIM delocalization index, DI). The present findings will contribute to further understanding of the origin and propagation of the relativistic effects influencing the experimental NMR parameters in heavy-element systems.