On the NICS limitations to predict local and global current pathways in polycyclic systems

Inostroza, Diego; García, Victor; Yáñez, Osvaldo; Torres‐Vega, Juan J.; Vásquez‐Espinal, Alejandro; Pino‐Rios, Ricardo; Báez‐Grez, Rodrigo; Tiznado, William

doi:10.1039/d1nj01510a

Cited by 28 publications

(40 citation statements)

References 56 publications

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“…The analysis used to identify the different ring current circuits has been performed according to the strategy initially proposed in references [46,59], which consists of establishing equations that account for the couplings of the different current flows. Note that this strategy has been used satisfactorily in our group in different recent works [60,61]. The integration planes used and the RCS values (total and partial: profiles) are reported in Figures S3-S5 in the Supplementary Material.…”

Section: Resultsmentioning

confidence: 91%

Persistent Planar Tetracoordinate Carbon in Global Minima Structures of Silicon-Carbon Clusters

Leyva‐Parra

Inostroza

Yáñez

et al. 2022

Atoms

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Recently, we reported a series of global minima whose structures consist of carbon rings decorated with heavier group 14 elements. Interestingly, these structures feature planar tetracoordinate carbons (ptCs) and result from the replacement of five or six protons (H+) from the cyclopentadienyl anion (C5H5−) or the pentalene dianion (C8H62−) by three or four E2+ dications (E = Si–Pb), respectively. The silicon derivatives of these series are the Si3C5 and Si4C8 clusters. Here we show that ptC persists in some clusters with an equivalent number of C and Si atoms, i.e., Si5C5, Si8C8, and Si9C9. In all these species, the ptC is embedded in a pentagonal C5 ring and participates in a three-center, two-electron (3c-2e) Si-ptC-Si σ-bond. Furthermore, these clusters are π-aromatic species according to chemical bonding analysis and magnetic criteria.

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Section: Resultsmentioning

confidence: 91%

Persistent Planar Tetracoordinate Carbon in Global Minima Structures of Silicon-Carbon Clusters

Leyva‐Parra

Inostroza

Yáñez

et al. 2022

Atoms

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“…The π-component exhibits a strong diatropic region around the whole Si 3 C 5 and Si 4 C 8 ring (long-range), in agreement with the presence of a global diatropic ring current. As indicated previously [61,92], the NICS analysis does not allow the identification of all the ring current circuits. However, it is a suitable complement to understand the magnetic behavior of these species and the interpretation of their aromaticity under the magnetic criterion.…”

Section: Nics Analysismentioning

confidence: 98%

“…In contrast, we describe the "global ring current" circuit as distributed around the whole molecule. This assignment was introduced by Sundholm et al [61] and recently used by our group to highlight the shortcomings of the NICS in assessing the aromaticity of polycyclic systems [92]. Note that Aihara introduced a similar concept to distinguish between different current density pathways [93].…”

Section: Current Density Analysismentioning

confidence: 99%

“…In this way, it is possible to computationally determine the local and global character of the induced currents. The strength of the local currents (diatropic) is computed and then subtracted from the strength of the diatropic current connecting the local rings to determine the global RCS [61,92]. Accordingly, it has been possible to identify the different delocalization circuits in the studied systems (part b of Figures 3 and 4).…”

Section: Current Density Analysismentioning

confidence: 99%

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Analysis of Local and Global Aromaticity in Si3C5 and Si4C8 Clusters. Aromatic Species Containing Planar Tetracoordinate Carbon

Torres‐Vega¹,

Alcoba

Oña

et al. 2021

Chemistry

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The minimum energy structures of the Si3C5 and Si4C8 clusters are planar and contain planar tetracoordinate carbons (ptCs). These species have been classified, qualitatively, as global (π) and local (σ) aromatics according to the adaptive natural density partitioning (AdNDP) method, which is an orbital localization method. This work evaluates these species’ aromaticity, focusing on confirming and quantifying their global and local aromatic character. For this purpose, we use an orbital localization method based on the partitioning of the molecular space according to the topology of the electronic localization function (LOC-ELF). In addition, the magnetically induced current density is analyzed. The LOC-ELF-based analysis coincides with the AdNDP study (double aromaticity, global, and local). Moreover, the current density analysis detects global and local ring currents. The strength of the global and local current circuit is significant, involving 4n + 2 π- and σ-electrons, respectively. The latter implicates the Si-ptC-Si fragment, which would be related to the 3c-2e σ-bond detected by the orbital localization methods in this fragment.

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“…Of significant note though, there have been some developments of the NICS index [37, 38] showing that it is not a single average NICS value , but rather only the single NICS(0) πzz or NICS(1) πzz component of it that needs to be used to more rigorously quantify aromaticity by a single theoretical value [22,39–41] . The relationship of NICS, part(s) or traces of it and the current density analysis to indicate aromaticity and anti‐aromaticity has been comprehensively studied and unequivocally proved [42–47] …”

Section: Computational Detailsmentioning

confidence: 99%

Cyclazines‐Structure and Aromaticity or Antiaromaticity on the Magnetic Criterion

Kleinpeter

Koch

2022

Eur J Org Chem

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Structure and spatial magnetic properties, through‐space NMR shieldings (TSNMRSs), of all ten cycl[2.2.2]azine to cycl[4.4.4]azine, hetero‐analogues and the corresponding hydrocarbons have been calculated at the B3LYP/6‐311G(d,p) theory level using the GIAO perturbation method and employing the nucleus independent chemical shift (NICS) concept. The TSNMRS values (actually, the ring current effect as measurable in 1H NMR spectroscopy) are visualized as iso‐chemical‐shielding surfaces (ICSS) of various size and direction, and employed to readily qualify and quantify the degree of (anti)aromaticity. Results are confirmed by NMR [δ(1H)/ppm, δ(15N)/ppm] and geometry (planar, twisted, bow‐shaped) data. The cyclazines N[2.2.2]− up to N[2.4.4]− are planar or at most slightly bowl‐shaped and, due to coherent peripheral ring currents (except in N[2.3.3]−, N[2.3.4], N[3.3.4]+ and N[2.4.4]+), develop aromaticity or anti‐aromaticity of the whole molecules dependent on the number of peripheral conjugated π electrons. The cyclazines N[2.3.3]−, N[2.3.4], N[3.3.4]+ and N[2.4.4]+ develop two ring currents of different direction within the same molecule, in which the dominating ring current proves to be paratropic (in N[3.3.4]+ diatropic) including the nodal N pz lone pair into the conjugation. The residual cyclazines N[3.4.4], N[4.4.4]− and N[4.4.4]+ are heavily twisted and, therefore, are not developing peripheral or diverse ring currents. The TSNMRS information about cyclazines and the parent tricyclic annulene analogues is congruent subject to structure and number of peripheral or internal conjugated π electrons, the corresponding (anti)aromaticity is in unequivocal accordance with Hückel's rule.

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On the NICS limitations to predict local and global current pathways in polycyclic systems

Abstract: Here, we analyze the possibility of predicting local and global current densities in a series of bicyclic hydrocarbons with 4n and 4n+2 -electrons from the nucleus-independent chemical shifts (NICS) computations....

Cited by 28 publications

References 56 publications

Persistent Planar Tetracoordinate Carbon in Global Minima Structures of Silicon-Carbon Clusters

Persistent Planar Tetracoordinate Carbon in Global Minima Structures of Silicon-Carbon Clusters

Analysis of Local and Global Aromaticity in Si3C5 and Si4C8 Clusters. Aromatic Species Containing Planar Tetracoordinate Carbon

Cyclazines‐Structure and Aromaticity or Antiaromaticity on the Magnetic Criterion

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