Neural networks are computational tools able to apprehend non-linear relationships between different parameters, having the capacity to order a large amount of input data and transform them into a graphical pattern of output data. We have previously reported their use for the quantification of the aromaticity through the Euclidean distance between neurons. In this article, we apply the method t...

A new aromaticity definition is advanced as the compactness formulation through the ratio between atoms-in-molecule and orbital molecular facets of the same chemical reactivity property around the pre- and post-bonding stabilization limit, respectively. Geometrical reactivity index of polarizability was assumed as providing the benchmark aromaticity scale, since due to its observable character;...

The local aromaticity of the six-membered rings in three series of benzenoid compounds, namely, the [n]acenes, [n]phenacenes, and [n]helicenes for n = 1-9, has been assessed by means of three probes of local aromaticity based on structural, magnetic, and electron delocalization properties. For [n]acenes our analysis shows that the more reactive inner rings are more aromatic than the outer rings...

The local aromaticity of a series of benzenoid systems was determined through the use of structurally (HOMA) and magnetically (NICS) based measures, and also by using a new electronically based indicator of aromaticity, the para-delocalization index (PDI). The results were compared with the predictions of Clar’s aromatic -sextet rule. It is found that, for all analyzed benzenoid hydrocarbons ha...

In this work, we analyze the geometry and electronic structure of the [X(n)M(3)](n-2) species (M = Be, Mg, and Ca; X = Li, Na, and K; n = 0, 1, and 2), with special emphasis on the electron delocalization properties and aromaticity of the cyclo-[M(3)](2-) unit. The cyclo-[M(3)](2-) ring is held together through a three-center two-electron bond of sigma-character. Interestingly, the interaction ...

This work introduces a new local aromaticity measure, defined as the mean of Bader's electron delocalization index (DI) of para-related carbon atoms in six-membered rings. This new electronic criterion of aromaticity is based on the fact that aromaticity is related to the cyclic delocalized distribution of pi-electrons. We have found that this DI and the harmonic oscillator model of aromaticity...

The relative aromaticity of benzenoid rings in the linear polyacenes is investigated using two novel aromaticity approaches. According to the first, the aromaticity of individual benzene rings was gauged by the values of six-center bond indices (SCI) calculated within the so-called Generalized Population Analysis (GPA). In the second approach, the same goal is addressed using the theory of Mole...

Electronic structure calculations (B3LYP/6-311+G**) predict that nucleophilic attack of the aromatic cycloCu4(μ)4 ring yields ligand-stabilized tetranuclear Cu4 clusters formulated as cyclo-Cu4(μ)4Nucn (n = 1-4; Nuc = N2, CO, H2O, NH3 and PH3). Depending on the number of added nucleophiles, the tetranuclear Cu4 clusters adopt planar, bent or 3D tetrahedral geometries. These molecules exhibit ar...

Aromaticity is a property usually linked to the ground state of stable molecules. Although it is well-known that certain excited states are unquestionably aromatic, the aromaticity of excited states remains rather unexplored. To move one step forward in the comprehension of aromaticity in excited states, in this work we analyze the electron delocalization and aromaticity of a series of low-lyin...

In this work, we have analyzed the local aromaticity of the six-membered rings (6-MRs) of planar and pyramidalized pyracylene species through the structurally based harmonic oscillator model of aromaticity (HOMA), the electronically based para-delocalization index (PDI), and the magnetic-based nucleus independent chemical shift (NICS) measurements, as well as with maps of ring current density. ...