A study on the aromaticity and magnetic properties of N-confused porphyrins

In this paper, topological resonance energy (TRE) methods were used to describe the global aromaticity of nitrogen confused porphyrin (NCP) isomers. The TRE results show that all NCP isomers exhibit lower aromaticity than the normal porphyrins, and their aromaticity decreases as the number of confused pyrrole rings in the molecule increases. In the NCPs, global aromaticity decreases as the distance between the nitrogen atoms increases. The bond resonance energy (BRE) and circuit resonance energy (CRE) indices were applied to study local aromaticity and conjugated pathways. Both the BRE and CRE indices revealed that individual pyrrolic subunits maintain their strong aromatic character and are the main source of global aromaticity. Ring currents (RC) were analysed using the Hückel–London model. RC results revealed that the macrocyclic electron conjugation pathway is the main source of diatropicity. As the number of confused pyrrole rings in the molecule increases, its diatropicity gradually decreases. In the confused pyrrole rings of the NCP isomers, the diatropic RC passing through the β -positions is always weaker than that passing through the inner sections. This is unrelated to the location of the protonated or non-protonated nitrogen atom at the periphery of the molecule and must be ascribed to the unique properties of the confused pyrrole rings.

A study on the aromatic conjugation pathways and the ring currents of bridged [18]annulenes

The topological resonance energy method was used to investigate the global aromaticity of a set of [18]annulene-derived compounds obtained by replacing two, four, or all six of the inner hydrogen atoms with bridges (oxygen, imino-, sulfur, or combinations of the three).

A study on the aromaticity and ring currents of dithienopyridines and dithienobenzene

The global aromaticity of dithienopyridine and dithienobenzene isomers was investigated using the topological resonance energy (TRE) and percentage topological resonance energy (%TRE) methods. The effect of variations in the positions of sulfur and nitrogen atoms on [Formula: see text]-electron delocalization is analyzed. The local aromaticity of these isomers is described based on the bond resonance energy (BRE) and circuit resonance energy (CRE) methods. Our BRE and CRE results show that structure of the central six-membered rings has a strong effect on global aromaticity. The aromaticity of these dithienopyridine isomers is enhanced when a complete pyridine unit exists in their middle ring structure, while the aromaticity of the dithienobenzene isomers is enhanced when a complete benzene unit exists in their middle ring structure. For dithienopyridines, our results obtained using the TRE method correlate well with the Bird aromaticity index as reported in the literature. Our ring-current results show that all these compounds are diatropic systems.

Systematic investigation of the stability of all dihydro isomers of the more stable C38 fullerene isomer with C2 symmetry

The local aromaticity of fullerene C[Formula: see text] ([Formula: see text] was studied using the bond resonance energy (BRE) method. The global aromaticity of all 349 possible isomers of C[Formula: see text]H2 based on [Formula: see text] symmetry was investigated using the topological resonance energy (TRE) method. The TRE results show that most of the C[Formula: see text]H2 isomers have greater stability than C[Formula: see text] ([Formula: see text]. Based on the BRE results, the preferred addition sites of hydrogen atoms are discussed. The relationship between the addition sites and BREs is analyzed and discussed. We found that the addition sites of hydrogen atoms are strongly dependent on the magnitude of the parent cage BRE values. The most stable isomers of C[Formula: see text]H2 are often produced by diminishing of the [Formula: see text]-bonds from those sites in the parent cage at which are located the two carbon atoms with the lowest BRE values. Based on this rule, the preferred addition patterns for non-IPR fullerene cages can be easily predicted.

A study of the aromaticity and ring currents of azulene and azaazulenes

The global aromaticity of azaazulenes has been investigated using topological resonance energy (TRE), percentage topological resonance energy (% TRE), and magnetic resonance energy (MRE) methods.

Magnetic resonance energy and topological resonance energy

Magnetic resonance energy (MRE) derived from the ring-current diamagnetic susceptibility was examined in conjunction with topological resonance energy (TRE).