Aromaticity in heterocyclic analogues of benzene: Dissected NICS and current density analysis

Abstract

The magnetic aromaticity of 6‐membered monoheterocycles containing Group 13 to 16 elements (C5H5X, where X = SiH, GeH, N, P, As, O+, S+, Se+) was assessed by using 2 magnetic descriptors: the π‐electron contribution to the out‐of‐plane component of the nucleus‐independent chemical shifts (NICSzz,π) and ring current strength. The results show that both descriptors lead to the same conclusion regarding magnetic aromaticity. However, they do not agree with the predictions obtained by isotropic NICS, which is a most commonly used method. Ring current strength and NICSπ predict that benzene is the most aromatic molecule of the series, with an only slightly less aromatic pyridine. Additionally, aromaticity decreases when going down in the same group of the periodic system. The only exception is the pyrylium cation, which is predicted as the least aromatic species of this series.

Aromatic nature of neutral and dianionic 1,4-diaza-2,3,5,6-tetraborinine derivatives

“…66 It has been demonstrated that NICS pzz in addition to NICS zz (1) could be the most reliable aromaticity indexes, with statistically good correlation with aromatic stabilization energies. 64,69 The NICS zz values of 3 [NICS zz (1) (1)…”

Interpreting Aromaticity and Antiaromaticity through Bifurcation Analysis of the Induced Magnetic Field

“…Previous studies, based on ring currents strengths and NICS zz evaluations, suggest that all pnictogen heterobenzenes are strongly aromatic; moreover, their aromaticity decreases as the heteroatom size increases. [25] As we can see in Figure 4, all the C 5 H 5 X (where X = N, P, As, Sb, Bi) systems are less aromatic than benzene, but they remain strongly aromatic with bifurcation values between À 35 and À 45 ppm for bismine and arsinine, respectively. However, the order of aromaticity (predicted by the bifurcation value) does not follow a periodic trend.…”

“…The , has been analyzed using different strategies. For instance, two‐dimensional maps have been used by several authors to describe the electronic delocalization–,, and, more recently, the chemical bond in different compounds. These maps provide more detail regarding the delocalization of various systems and have been applied qualitatively to describe aromaticity.…”

Vorticity: Simplifying the analysis of the current density

“…It can also be used to study the electron delocalization in bonds and molecules . Moreover, this vector field has been extensively used to study and evaluate one of the most important concepts in chemistry, the aromaticity . This concept is not a physical observable, therefore, several indices based in the geometric, energetic, electronic, and magnetic properties have been proposed to evaluate it .…”