Aromaticity magnetic criteria

Thus aromaticity in cyclopropenone cannot be detected by the magnetic criterion although it is suggested by other chemical and physical properties. UV, IR, and -NMR data of cyclopropenone are summarized in Table 6, but are discussed in later chapters. 

In discussing various indices of aromaticity developed from different criteria (energetic, structural, magnetic), we noted correlations between indices based not only on one type of criteria, but also on different ones. Is, however, the interrelation among different criteria always clear-cut and convincing Will the aromaticity inferred from, say, a magnetic criterion be confirmed by an energetic one ... 

The main computational criteria used for determining aromaticity are (a) the geometric criterion, (b) the energetic criterion, (c) the magnetic criterion. These criteria are discussed below. 

The magnetic criterion is, however, not a unique indicator of aromaticity. The linear polymethinium ions 42... 

The negative values of the calculated NICS indexes (restricted Hartree-Eock RHE)/6-31- -G wavefunctions of the most stable B3LYP/6-311G geometries), examined as a magnetic criterion for aromaticity, indicate that all species have aromatic character. The NICS values for anthranil are remarkably different evidencing a loss of... 

According to this analysis, Hfj in the singlet electronic state has three 2c-2e Hf-Hf o-bonds formed of hybrid 6s-, 5d-AOs and three completely delocalized bonds formed of pure d-AOs one completely bonding 3c-2e d-radial-based o-bond responsible for the presence of o-aromaticity, one completely bonding 3c-2e d-radial-based tr-bond responsible for the presence of ir-aromatidty, and one completely bonding 3c-2e d-AO-based 8-bond responsible for the presence of 8-aromaticity in this cluster (4n -F 2 rule for every kind of aromaticity for n = 0). The 3c-2e d-AO-based 5-bond is formed by the overlap of the d 2 AO on each Hf atom. The triple aromaticity is consistent with the bond equalization and high symmetry of Hfj. Tsipis et al. [119] obtained NlCS -scan curve for D3, A/ state of Hf3, Ti3 and Zr3 clusters, and concluded that they all three are indeed triply (a-, tr- and 5-) aromatic in this state on the basis of magnetic criterion. 

It is evident that the 5f orbitals of the uranium metal centers play a key role in the bonding of the aforementioned f-block metal systems significantly contributing to the cyclic electron delocalization and the associated magnetic diatropic response. The aromaticity of the cyclo-U X (n = 3,4 X = OH, NH) and cycZo-U (/tt2-X) (n = 3, 4 X = C, CH, NH) clusters was verified by the magnetic criterion of... 

Pelloni S, Lazzeretti P (2013) Polygonal current model an effective quantified of aromaticity on the magnetic criterion. J Phys Chem A 117 9083-9092... 

Estimation of resonance energy by spin-coupled valence bond calculations [129] and the application of newly developed aromaticity indices considering the cyclic x-electron delocalization [142, 143] have confirmed that [3]- and [6]radialene are nonaromatic. As far as the magnetic criterion for aromaticity of conjugated... 

The stepwise transfer of electrons from alkali metals to Ti-conjugated systems enables the study of the relationship between the number of Ti-electrons and the aromatic/antiaromatic properties of the systems vis d vis the Hiickel rule. The magnetic criterion for aromaticity serves as a probe for the aromatic nature of the systems under study. 

In a review, Gorelik51 has shown that magnetic, structural, and energetic properties are determined by the electronic structure of cyclic conjugated systems, which are stabilized by a cyclic delocalization of electrons. Chemical reactivity cannot serve satisfactorily as a general criterion of aromaticity. 

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