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Nowadays, an active research topic is the connection between Clar's rule, aromaticity, and magnetic properties of polycyclic benzenoid hydrocarbons. In the present work, we employ a meticulous magnetically induced current density analysis to define the net current flowing through any cyclic circuit, connecting it to aromaticity based on the ring current concept. Our investigation reveals that the analyzed polycyclic systems display a prominent global ring current, contrasting with subdued semi‐local and local ring currents. These patterns align with Clar's aromatic π‐sextets only in cases where migrating π‐sextet structures are invoked. The results of this study will enrich our comprehension of aromaticity and magnetic behavior in such systems, offering significant insights into coexisting ring current circuits in these systems. [ABSTRACT FROM AUTHOR]

Despite the central role of aromaticity in the chemistry of expanded porphyrins, the evaluation of aromaticity remains difficult for these extended macrocycles. The presence of multiple conjugation pathways and different planar and nonplanar π‐conjugation topologies makes the quantification of global and local aromaticity even more challenging. In neutral expanded porphyrins, the predominance of the aromatic conjugation pathway passing through the imine‐type nitrogens and circumventing the amino NH groups is established. However, for charged macrocycles, the question about the main conjugation circuit remains open. Accordingly, different conjugation pathways in a set of neutral, anionic, and cationic expanded porphyrins were investigated by means of several aromaticity indices rooted in the structural, magnetic, and electronic criteria. Overall, our results reveal the predominance of the conjugation pathway that passes through all nitrogen atoms to describe the aromaticity of deprotonated expanded porphyrins, while the outer pathway through the perimeter carbon atoms becomes the most aromatic in protonated macrocycles. In nonplanar and charged macrocycles, a discrepancy between electronic and magnetic descriptors is observed. Nevertheless, our work demonstrates AVmin remains the best tool to determine the main conjugation pathway of expanded porphyrins. [ABSTRACT FROM AUTHOR]

The reduction of N,C,N-chelated antimony(III) chlorides [C6H3-2,6-(CH=NR)2]SbCl2 (R=Ph ( 1), tBu ( 2), Dip ( 3); Dip=2,6- iPr2C6H3) with an appropriate amount of KC8 or Li[AlH4] resulted in the formation of rare examples of monomeric stibinidenes [C6H3-2,6-(CH=NR)2]Sb (R=Ph ( 4), tBu ( 5), Dip ( 6)). Similarly, the reduction of compounds 1 or 2 by two equivalents of K[B( sBu)3H] led to the stibinidenes 4 and 5. In contrast, the analogous reaction of compound 3 resulted in the formation of an unprecedented stibinidene [C6H3-2-(CH=NR)-6-(CH2NHR)]Sb ( 7) (R=Dip), in which the hydrogen atoms that come from the K[B( sBu)3H] are incorporated into the ligand backbone. To gain further insight into this intriguing reactivity with K[B( sBu)3H] and to assess the influence of the substitution at both the antimony atom and pendant substituents, we prepared compounds [C6H3-2-(CH=NDip)]Sb(Ph)Cl ( 8) and [C6H2-2-(CH=NDip)-4,6-( tBu)2]SbCl2 ( 9). The treatment of compound 8 with K[B( sBu)3H] smoothly led to the 1-Ph-2-Dip-1 H-2,1-benzazastibole ( 11), whereas the reaction of compound 9 with K[B( sBu)3H] resulted in either tBu-substituted 1-Cl-2-Dip-1 H-2,1-benzazastibole ( 13) or the formation of unprecedented Sb−Sb dimer bis(2-Dip-1 H-2,1-benzazastibole) ( 12) depending on the reaction stoichiometry. The miscellaneous reactivity of antimony(III) precursors with reducing agents together with the structure and bonding of the resulting products has also been investigated from a theoretical point of view. [ABSTRACT FROM AUTHOR]

The reduction of N,C,N-chelated bismuth chlorides [C6H3-2,6-(CHNR)2]BiCl2 [where R= tBu ( 1), 2′,6′-Me2C6H3 ( 2), or 4′-Me2NC6H4 ( 3)] or N,C-chelated analogues [C6H2-2-(CHN-2′,6′- iPr2C6H3)-4,6-( tBu)2]BiCl2 ( 4) and [C6H2-2-(CH2NEt2)-4,6-( tBu)2]BiCl2 ( 5) is reported. Reduction of compounds 1- 3 gave monomeric N,C,N-chelated bismuthinidenes [C6H3-2,6-(CHNR)2]Bi [where R= tBu ( 6), 2′,6′-Me2C6H3 ( 7) or 4′-Me2NC6H4 ( 8)]. Similarly, the reduction of 4 led to the isolation of the compound [C6H2-2-(CHN-2′,6′- iPr2C6H3)-4,6-( tBu)2]Bi ( 9) as an unprecedented two-coordinated bismuthinidene that has been structurally characterized. In contrast, the dibismuthene {[C6H2-2-(CH2NEt2)-4,6-( tBu)2]Bi}2 ( 10) was obtained by the reduction of 5. Compounds 6- 10 were characterized by using 1H and 13C NMR spectroscopy and their structures, except for 7, were determined with the help of single-crystal X-ray diffraction analysis. It is clear that the structure of the reduced products (bismuthinidene versus dibismuthene) is ligand-dependent and particularly influenced by the strength of the N→Bi intramolecular interaction(s). Therefore, a theoretical survey describing the bonding situation in the studied compounds and related bismuth(I) systems is included. Importantly, we found that the C3NBi chelating ring in the two-coordinated bismuthinidene 9 exhibits significant aromatic character by delocalization of the bismuth lone pair. [ABSTRACT FROM AUTHOR]

Noncovalent interactions involving aromatic rings, such as π-stacking and CH/π interactions, are central to many areas of modern chemistry. However, recent studies proved that aromaticity is not required for stacking interactions, since similar interaction energies were computed for several aromatic and aliphatic dimers. Herein, the nature and origin of π/π, σ/σ, and σ/π dispersion interactions has been investigated by using dispersion-corrected density functional theory, energy decomposition analysis, and the recently developed noncovalent interaction (NCI) method. Our analysis shows that π/π and σ/σ stacking interactions are equally important for the benzene and cyclohexane dimers, explaining why both compounds have similar boiling points. Also, similar dispersion forces are found in the benzene⋅⋅⋅methane and cyclohexane⋅⋅⋅methane complexes. However, for systems larger than naphthalene, there are enhanced stacking interactions in the aromatic dimers adopting a parallel-displaced configuration compared to the analogous saturated systems. Although dispersion plays a decisive role in stabilizing all the complexes, the origin of the π/π, σ/σ, and σ/π interactions is different. The NCI method reveals that the dispersion interactions between the hydrogen atoms are responsible for the surprisingly strong aliphatic interactions. Moreover, whereas σ/σ and σ/π interactions are local, the π/π stacking are inherently delocalized, which give rise to a non-additive effect. These new types of dispersion interactions between saturated groups can be exploited in the rational design of novel carbon materials. [ABSTRACT FROM AUTHOR]

The switching of topology between 'figure-eight', Möbius, and untwisted conformations in [32]heptaphyrins(1.1.1.1.1.1.1) has been investigated by using density functional theory calculations. Such a change is achieved by variation of one internal dihedral angle and, if properly controlled, can provide access to molecular switches with unique optical and magnetic properties. In this work, we have explored different conformational control methods, such as solvent, protonation and meso substituents. Despite its antiaromatic character, most of the [32]heptaphyrins (R=H, CH3, CF3, Ph, C6F5) adopt a figure-eight conformation in the neutral state, owing to their more-effective hydrogen-bonding interactions. The aromatic Möbius topology is only preferred with dichlorophenyl groups, which minimize the steric hindrance that arises from the bulky chlorine atoms. The conformational equilibrium is sensitive to the solvent, so polar solvents, such as DMSO, further stabilize the Möbius conformation. Protonation induces a conformational change into the Möbius topology, irrespective of the meso-aryl groups. In the triprotonated species, the conformational switch is blocked and a non-twisted conformer becomes much more stable than the figure-eight conformation. We have shown that the relative energies of the protonated [32]heptaphyrins are dominated by aromaticity. Importantly, this topology switching induces a dramatic change in the magnetic properties and reactivity of the macrocycles, as revealed by several energetic, magnetic, structural, and reactivity indices of aromaticity. [ABSTRACT FROM AUTHOR]

Noncovalent interactions involving aromatic rings, such as π ‐ stacking and CH/π interactions, are central to many areas of modern chemistry. In their Full Paper on page 4931 ff., M. Alonso et al. describe their investigations on the nature and origin of π/π, σ/σ and σ/π dispersion interactions by using dispersion ‐ corrected density functional theory, energy decomposition analysis and the noncovalent interaction method. The analysis confirms that π/π and σ/σ stacking interactions are equally important in energy for the benzene and cyclohexane dimers, but different in origin. These new types of dispersion interactions between saturated groups can be exploited in the rational design of novel carbon materials. [ABSTRACT FROM AUTHOR]