Unraveling aromaticity: the dual worlds of pyrazole, pyrazoline, and 3D carborane

• Zahra Noori,
• Miquel Solà,
• Clara Viñas,
• Francesc Teixidor and
• Jordi Poater

Beilstein J. Org. Chem. 2025, 21, 412–420, doi:10.3762/bjoc.21.29

• carborane and the π-aromaticity of the heterocycle are orthogonal, making a true 3D/2D aromatic system unachievable. The carborane is highly aromatic, generating highly negative NICS values (−25 to −30 ppm). We have observed that these high NICS values extend to fused rings, leading to incorrect estimations

• of aromaticity. Therefore, relying solely on NICS can be misleading, and other computational indicators, along with experimental or structural data, should be used to accurately assess aromaticity. Keywords: 3D aromaticity; carborane; density functional theory; NICS ambiguity; pyrazole

• assessed using indicators such as magnetic-based NICS, electronic-based MCI, or bond lengths, among others, given its multidimensional character [41][42][43]. Results and Discussion We have first analyzed a series o-carborane-fused pyrazoles involving the fusion to either a C–C, C–B or B–B bond in the

Oxidation of [3]naphthylenes to cations and dications converts local paratropicity into global diatropicity

• Abel Cárdenas,
• Zexin Jin,
• Yong Ni,
• Jishan Wu,
• Yan Xia,
• Francisco Javier Ramírez and
• Juan Casado

Beilstein J. Org. Chem. 2025, 21, 277–285, doi:10.3762/bjoc.21.20

• shift (NICS) calculations and anisotropy of the current induced density (ACID) plots, as they evidenced the presence of a perimetral diatropic global ring current upon oxidation. Keywords: ACID; aromaticity; force constants; NICS; spectroscopy; Introduction Since the discovery of conjugated polymers

• 1700 cm−1 Raman band) and in NAP for m-2 (marked by the triplet in the 1500–1600 cm−1 region). Nucleus-independent chemical shifts (NICS) Among the different criteria to evaluate aromaticity, magnetic properties are the most confident, as they are directly connected with the ring currents associated to

• electronic delocalization. In order to figure out the driving force that leads the stabilization of the oxidized species of 1 and 2, we calculated the NICS values of all fused rings in the neutral and cationic species of m-1 and m-2 (Figure 7), in order to obtain a precise and comparable measurement of the

Biphenylene-containing polycyclic conjugated compounds

• Cagatay Dengiz

Beilstein J. Org. Chem. 2023, 19, 1895–1911, doi:10.3762/bjoc.19.141

• structural designs. NICS (nucleus independent chemical shift) analysis revealed that the linear structures within the series exhibited reduced antiaromaticity in the CBD ring compared to other structural arrangements. By employing a methoxy group on the oxonorbornene, the methyl ether moiety can be removed

Unprecedented synthesis of a 14-membered hexaazamacrocycle

• Anastasia A. Fesenko and
• Anatoly D. Shutalev

Beilstein J. Org. Chem. 2023, 19, 1728–1740, doi:10.3762/bjoc.19.126

• deviation of 0.054 Å from the mean-square plane. The nuclear-independent chemical shift (NICS) [48][49][50] values of 5 in its optimized conformation were used as a magnetic criterion of aromaticity. The NICS(0) value for the macrocyclic ring (+2.23 ppm in DMSO), calculated at the HF/6-31+G(d) level, shows

• its somewhat anti-aromatic character. Obvious aromaticity of the pyrazole rings is confirmed by the NICS(0) values of −12.64 ppm. Macrocycle 5 has various reactive centers, including two amidrazone fragments with primary amino groups, which makes it possible to modify it in many ways [51][52][53][54

• macrocyclic core [NICS(0) = +2.23 ppm calculated at the HF/6-31+G(d) level]. Since numerous heterocyclic and carbocyclic analogs of 3-amino-1-methyl-1H-pyrazole-4-carbonitrile (3), which is the starting material in the synthesis of macrocycle 5, are readily available, we believe that our results will be

One-pot synthesis of dicyclopenta-fused peropyrene via a fourfold alkyne annulation

• Ji Ma,
• Yubin Fu,
• Junzhi Liu and
• Xinliang Feng

Beilstein J. Org. Chem. 2020, 16, 791–797, doi:10.3762/bjoc.16.72

• nucleus-independent chemical shift (NICS) calculation was conducted. As shown in Figure 2d, the positive NICS(1) values of the five-membered rings A and C reveal the slightly anti-aromatic feature. The rings B, F and I appear to have more aromatic character, while the rings D, E, G and H become less

• . Hydrogen atoms and solvent molecules are omitted for clarity. (d) Selected bond lengths (from the crystal structure) and calculated NICS(1) values of rings A–I in 1. (e) Clar valence structure representation of 1 with three benzeneoid rings. (a) UV–vis absorption spectra of precursor 5 and 1 in CH2Cl2

The activity of indenylidene derivatives in olefin metathesis catalysts

• Maria Voccia,
• Steven P. Nolan,
• Luigi Cavallo and
• Albert Poater

Beilstein J. Org. Chem. 2018, 14, 2956–2963, doi:10.3762/bjoc.14.275

• the phosphine release, and the relative stability of the corresponding metallacycle over classical ylidene ligands. Mayer bond orders and steric maps provide structural reasons for these effects, whereas NICS aromaticity and conceptual DFT confirm that the electronic parameters do not play a

• ]. In order to evaluate the change of the aromaticity of the phenyl ring of the indenylidene derivatives 3–6, we evaluated the aromaticity of the six-membered aryl rings, as well as the ring current on the five-membered ring by means of magnetic-based aromaticity criterion NICS (GIAO, see all NICS

• scaled by 1.17, and a mesh of 0.1 Å was used to scan the sphere for buried voxels. The steric maps were generated also with the SambVca package [69]. Aromaticity was evaluated by means of the nucleus independent chemical shift (NICS) [70][71], proposed by Schleyer et al., as a magnetic descriptor of

Synthesis and characterization of π–extended “earring” subporphyrins

• Haiyan Guan,
• Mingbo Zhou,
• Bangshao Yin,
• Ling Xu and
• Jianxin Song

Beilstein J. Org. Chem. 2018, 14, 1956–1960, doi:10.3762/bjoc.14.170

• antiaromatic character of the ear-containing macrocycle, which is quite similar to the analogous “earring” porphyrin [38]. Furthermore, the antiaromaticity of the ear-containing macrocycle is proved by the large positive NICS value in the hole as well as the anticlockwise ring currency (see Supporting

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

Interactions between tetrathiafulvalene units in dimeric structures – the influence of cyclic cores

• Huixin Jiang,
• Virginia Mazzanti,
• Christian R. Parker,
• Søren Lindbæk Broman,
• Jens Heide Wallberg,
• Karol Lušpai,
• Adam Brincko,
• Henrik G. Kjaergaard,
• Anders Kadziola,
• Peter Rapta,
• Ole Hammerich and
• Mogens Brøndsted Nielsen

Beilstein J. Org. Chem. 2015, 11, 930–948, doi:10.3762/bjoc.11.104

• that required to reduce the acyclic TEE compound 1a (−1.70 V vs Fc/Fc+) [10]. We explained this readiness of 2a to accommodate electrons by a gain of aromaticity; a resonance form with a 14 πz core can be drawn for the dianion and a diatropic ring-current was supported by NICS calculations. The new

Synthetic scope and DFT analysis of the chiral binap–gold(I) complex-catalyzed 1,3-dipolar cycloaddition of azlactones with alkenes

• María Martín-Rodríguez,
• Luis M. Castelló,
• Carmen Nájera,
• José M. Sansano,
• Olatz Larrañaga,
• Abel de Cózar and
• Fernando P. Cossío

Beilstein J. Org. Chem. 2013, 9, 2422–2433, doi:10.3762/bjoc.9.280

• : asymmetric catalysis; DFT; 1,3-dipolar cycloaddition; gold catalysis; NICS; NTR; oxazolones; prolines; Introduction The synthesis of α-amino acids employing an α-amino carbonyl template constitutes the most straightforward route to introduce the α-side chain [1]. As a valid example, oxazol-5-(4H)-ones

• described in a preliminary communication [28] concerning the catalytic activity of complexes 3 and 4 in the 1,3-DC of oxazolones with electrophilic alkenes. Here, a deep DFT analysis and the application of other computational experiments (NRT, NICS) were compared to the experimentally observed results in

• negative charge in the Lewis structure of Ylide I is mainly placed on C5. In the case of Ylide II, this negative charge is placed on the oxygen of the carboxy group instead. The importance of these electronic distributions was verified by Nucleus Independent Chemical Shifts (NICS) calculations in the ring

A quantitative approach to nucleophilic organocatalysis

• Herbert Mayr,
• Sami Lakhdar,
• Biplab Maji and
• Armin R. Ofial

Beilstein J. Org. Chem. 2012, 8, 1458–1478, doi:10.3762/bjoc.8.166

• chemical shifts (NICS) [109][110][111], which are considered to be a measure of aromaticity. In agreement with the almost equal lengths of the exocyclic C–C bonds in 45a (136.1 pm) and 45c (135.4 pm), as determined by X-ray crystallography, none of the two heterocyclic rings in 47a and 47c shows aromatic

• character (NICS(1)). However, while the electrophilic addition to the exocyclic double bond of 47a yields the cyclic conjugated 6π system in 48a, the analogous electrophilic addition to 47c yields the nonaromatic amidinium ion 48c. The high nucleophilicity of 45a, which is mirrored by the high proton

• ]) of the corresponding carbenes 49a–c (in kJ mol–1, MP2/6-31+G(2d,p)//B98/6-31G(d)), and the NICS(1) values of 47–49 (B3LYP/6-311+G(d)) (from [107]). Berkessel’s synthesis of a Breslow intermediate (51, keto tautomer) from carbene 43 [112]. Synthesis of O-methylated Breslow intermediates [114

Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues

• Helen Jansen,
• J. Chris Slootweg and
• Koop Lammertsma

Beilstein J. Org. Chem. 2011, 7, 1713–1721, doi:10.3762/bjoc.7.201

• -orbitals [41], as is the case for cyclohepta-1,3,5-triene (1) [19][20]. Through the use of nucleus-independent chemical shifts (NICS(1)) [48], it was shown that thiepine (−2.3 ppm) [49] and phenyl phosphepine (−4.8 ppm) [7] display aromatic character when compared to the well-known 6π-electron Hückel

• -aromatic tropylium cation [46], which has a NICS(1) value of −8.2 ppm. Adding electronegative substituents enhances the effect, and fully aromatic systems are obtained after complete fluorination of the heteropines (Figure 1) [50]. In contrast, the flattened transition structures for ring inversion of

• thiepine and phosphepine are indeed highly antiaromatic planar 8π-electron systems, with positive NICS(1) values of 19.3 [47] and 6.4 ppm [7], respectively. The inherent instability of thiepine (5) has been attributed to this effect [51][52]. Oxepine – benzene oxide Oxepine (3) was isolated first by Vogel