A study on the aromaticity and conjugation pathways of diheterodiazuliporphyrins and their dications

Abstract

The aromaticity of a series of diheterodiazuliporphyrins, both in the neutral and the dicationic states, has been investigated using the topological resonance energy (TRE) method. Our TRE results show that in each of the dicationic states, all the diheterodiazuliporphyrin isomers have greater aromaticity than when in their corresponding neutral states. An evaluation of the local aromaticity and of the main aromatic conjugation pathways has been carried out through the use of the bond resonance energy (BRE) and circuit resonance energy (CRE) indices, both in the neutral and dicationic states. Our BRE and CRE results show that the local aromaticity arising from the small rings is much larger and is a greater contributor to global aromaticity than the aromaticity which arises from the main aromatic conjugation pathway. In their neutral states, the azulene units are the main contributors to global aromaticity and the compounds themselves are stabilized primarily by their 10π‐electron peripheral structures. In their dicationic states however, it is the 6π‐electron tropylium unit structures which are the main contributors to the global aromaticity. The strength of the magnetically induced ring current (RC) has been calculated using the Hückel‐London model. The RC results show that current strength and the direction of the induced RC of the macrocyclic circuit play a crucial role in determining the paratropicity or diatropicity of the compound. The correlation between the observed 1H NMR chemical shift and the RC strength is discussed, and good correlation is obtained. Finally, the main impact factors upon aromaticity and the RCs are clarified.

A study on the aromaticity and ring currents of polycyclic neutral oxocarbon isomers

“…In general, large circuits make proportionately large contributions to overall RCs, whereas small circuits make small contributions. [ 35 ] However, for polycyclic neutral oxocarbons, according to the results in Tables 2 and S1, it is obvious that in all cases, large circuits make only a small aromatic contribution and a small CC contribution to these molecules. That is to say, in these compounds, the magnitude of the RC does not directly correspond with the size of the circuits.…”

“…In the continuation of our work on the aromaticity of polycyclic heteroaromatic compounds, [ 35 ] we investigated some of the polycyclic neutral oxocarbons. Toward that end, we selected two descriptors to predict the global aromaticity of a series of polycyclic neutral oxocarbons: the TRE approach (an energetic index), [ 24–27 ] and the RC approach (a magnetic index).…”

Tropylium Ion, an Intriguing Moiety in Organic Chemistry

“…At a fundamental level, this transformation is intriguing since the non-benzenoid aromatic tropylium ring is altered into the aromatic benzene ring [108]. Using the topological resonance energy (TRE) method, Tuerhong, M., and Kerim, A., investigated the aromaticity of a series of diheterodiazuliporphyrins in both neutral (56a) and dicationic states (56b) [109]. The TRE results indicated that all isomers of diheterodiazuliporphyrins exhibited greater aromaticity in the dicationic states compared to their corresponding neutral states.…”

“…In the neutral states, the azulene units were the primary contributors to global aromaticity, and the compounds were primarily stabilized by their 10π-electron peripheral structures. However, in their dicationic states, the main contributors to global aromaticity were the 6π-electron tropylium unit structures [109] (Figure 23). The tropylium ion and its derivatives extend their applications in host-guest chemistry and polymerization chemistry.…”

“…The formation of charge-transfer (CT) complexes from 2,6-helic [6]arene hosts and a tropylium cation is one example of the host-guest chemistry of the tropylium ion. It was discovered that a redox stimulus could efficiently control the binding and release processes of the guest in the complexes, and the response process could Using the topological resonance energy (TRE) method, Tuerhong, M., and Kerim, A., investigated the aromaticity of a series of diheterodiazuliporphyrins in both neutral (56a) and dicationic states (56b) [109]. The TRE results indicated that all isomers of diheterodiazuliporphyrins exhibited greater aromaticity in the dicationic states compared to their corresponding neutral states.…”