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Artigas A, Carissan Y, Hagebaum-Reignier D, Bock H, Durola F, Coquerel Y. Aromaticity in Semi-Condensed Figure-Eight Molecules. Chemistry 2024; 30:e202401016. [PMID: 38642001 DOI: 10.1002/chem.202401016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2024] [Revised: 04/08/2024] [Accepted: 04/19/2024] [Indexed: 04/22/2024]
Abstract
Electron delocalization and aromaticity was comparatively evaluated in recently synthesized figure-eight molecules made of two condensed U-shaped polycyclic aromatic hydrocarbon moieties connected either by two single bonds or by two para-phenylene groups. The selected examples include molecules that incorporate eight-membered and sixteen-membered rings, as well as a doubly [5]helicene-bridged (1,4)cyclophane. We probe whether some electron delocalization could occur through the stereogenic single bonds in these molecules: Is aromaticity purely (semi-)local, or possibly also global in these molecules? It was concluded that the situation can go from a purely (semi-)local character when the dihedral angle at the connecting single bonds is large, such as in biphenyl, to a predominantly (semi-)local character with a minor global contribution when the dihedral angle is small, such as in the para-phenylene connectors of the [5] helicene-bridged cyclophane.
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Affiliation(s)
- Albert Artigas
- Facultat de Ciències, Universitat de Girona, Campus Montilivi, Carrer de Maria Aurèlia Capmany i Farnès 69, 17003, Girona, Catalunya, Spain
| | - Yannick Carissan
- Aix Marseille Univ, CNRS, Centrale Méditerranée, iSm2, Marseille, France
| | | | - Harald Bock
- Centre de Recherche Paul Pascal, CNRS, 115 av. Schweitzer, 33600, Pessac, France
| | - Fabien Durola
- Centre de Recherche Paul Pascal, CNRS, 115 av. Schweitzer, 33600, Pessac, France
| | - Yoann Coquerel
- Aix Marseille Univ, CNRS, Centrale Méditerranée, iSm2, Marseille, France
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Cummings E, Karadakov PB. Aromaticity in the Electronic Ground and Lowest Triplet States of Molecules with Fused Thiophene Rings. Chemistry 2024; 30:e202303724. [PMID: 38038597 DOI: 10.1002/chem.202303724] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2023] [Revised: 11/30/2023] [Accepted: 12/01/2023] [Indexed: 12/02/2023]
Abstract
Analysis of the variations of the off-nucleus isotropic magnetic shielding, σiso(r), around thiophene, thienothiophenes, dithienothiophenes and sulflowers in their electronic ground (S0) and lowest triplet (T1) states reveals that some of the features of aromaticity and bonding in these molecules do not fit in with predictions based on the popular Hückel's and Baird's rules. Despite having 4n π electrons, the S0 states of the sulflowers are shown to be aromatic, due to the local aromaticities of the individual thiophene rings. To reduce its T1 antiaromaticity, the geometry of thiophene changes considerably between S0 and T1: In addition to losing planarity, the carbon-carbon two 'double' and one 'single' bonds in S0 turn into two 'single' and one 'double' bonds in T1. Well-defined Baird-style aromaticity reversals are observed between the S0 and T1 states of only three of the twelve thiophene-based compounds investigated in this work, in contrast, the sulflower with six thiophene rings which is weakly aromatic in S0 becomes more aromatic in T1. The results suggest that the change in aromaticity between the S0 and T1 states in longer chains of fused rings is likely to affect mostly the central ring (or the pair of central rings); rings sufficiently far away from the central ring(s) can retain aromatic character.
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Affiliation(s)
- Edward Cummings
- Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK
| | - Peter B Karadakov
- Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK
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Fowler PW, Anstöter CS. Tuning (Anti)Aromaticity: Variations on the [8]-Circulene Framework. Chemphyschem 2024; 25:e202300791. [PMID: 38279875 DOI: 10.1002/cphc.202300791] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Revised: 01/10/2024] [Accepted: 01/22/2024] [Indexed: 01/29/2024]
Abstract
Optoelectronic properties of organic molecules are underpinned by delocalisation and delocalisability of π-electrons. These properties are sensitive to small changes in electron count, whether achieved by heteroatom substitution or redox chemistry. One measure of the delocalisability of π-electrons is the current induced by an external magnetic field, which is diagnostic of (anti)aromaticity. The ab initio ipsocentric method is used here to model diverse ring-current patterns in the family of [8]-circulenes based on tetracyclopenta[def,jkl,pqr,vwx]tetraphenylene (TCPTP), in different charge states, with disjoint hetero-atom substitution, and with CC units systematically replaced by BN pairs. Maps calculated at the CHF/CTOCD-DZ2/6-31G** level reveal that these modifications of the TCPTP framework access the full range of possibilities for current from concentric global circulations (typically counter rotating) to full (non-aromatic) localisation. In the ipsocentric approach, induced current density is partitioned into robust orbital contributions that obey selection rules based on orbital symmetry, energy and nodal character. The selection rules are applied here to interpret current-density and exploit insights gained from simpler models to suggest design strategies for fine-tuning of π-delocalisability (aromaticity and antiaromaticity) in macrocyclic frameworks.
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Affiliation(s)
- Patrick W Fowler
- Department of Chemistry, University of Sheffield, Sheffield, United Kingdom
| | - Cate S Anstöter
- School of Chemistry, University of Edinburgh, Edinburgh, Edinburgh, United Kingdom
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Leyva-Parra L, Pino-Rios R. Update for Isomerization Stabilization Energies: The Fulvenization Approach. ACS OMEGA 2024; 9:1436-1442. [PMID: 38222592 PMCID: PMC10785285 DOI: 10.1021/acsomega.3c07881] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/09/2023] [Revised: 11/28/2023] [Accepted: 12/04/2023] [Indexed: 01/16/2024]
Abstract
An alternative approach for calculating aromatic stabilization energies is proposed based on transforming an (anti)aromatic ring into a fulvene isomer. This fulvenization process gives a value of 34.05 kcal·mol-1 for benzene in the singlet state and a value of -17.85 kcal·mol-1 in the triplet state. Additionally, it is possible to use experimental values (as long as they exist) for the calculation as the gas-phase formation enthalpies of benzene and fulvene, whose difference is 33.72 kcal·mol-1. On the other hand, this same approach has been evaluated on several six-membered rings, including those persubstituted, biradicals, azines, and inorganic analogues, giving results in agreement with those reported in the literature using different criteria. Additionally, it is possible to differentiate the aromaticity of the rings in polycyclic aromatic hydrocarbons according to Clar's rules. Assigning the (anti)aromatic character in various nonbenzenoid rings (neutral and charged), except for five- and seven-membered rings, is also possible. The construction of the fulvene isomers in PAHs is set such that nonaromaticity-related effects are not considered. The results show that the fulvenization approach is an effective and efficient approach that can serve as an alternative or complement to existing tools.
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Affiliation(s)
- Luis Leyva-Parra
- Departamento
de Ciencias Químicas, Centro de Química Teórica
& Computacional (CQT&C), Universidad
Andrés Bello, Facultad de Ciencias Exactas, Avenida República 275, 8370146 Santiago de Chile, Chile
| | - Ricardo Pino-Rios
- Instituto
de Estudios de la Salud, Universidad Arturo
Prat, 1100000 Iquique, Chile
- Química
y Farmacia, Facultad de Ciencias de la Salud, Universidad Arturo Prat, Casilla 121, 1100000 Iquique, Chile
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Leyva-Parra L, Pino-Rios R, Inostroza D, Solà M, Alonso M, Tiznado W. Aromaticity and Magnetic Behavior in Benzenoids: Unraveling Ring Current Combinations. Chemistry 2024; 30:e202302415. [PMID: 37955853 DOI: 10.1002/chem.202302415] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2023] [Indexed: 11/14/2023]
Abstract
Nowadays, an active research topic is the connection between Clar's rule, aromaticity, and magnetic properties of polycyclic benzenoid hydrocarbons. In the present work, we employ a meticulous magnetically induced current density analysis to define the net current flowing through any cyclic circuit, connecting it to aromaticity based on the ring current concept. Our investigation reveals that the analyzed polycyclic systems display a prominent global ring current, contrasting with subdued semi-local and local ring currents. These patterns align with Clar's aromatic π-sextets only in cases where migrating π-sextet structures are invoked. The results of this study will enrich our comprehension of aromaticity and magnetic behavior in such systems, offering significant insights into coexisting ring current circuits in these systems.
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Affiliation(s)
- Luis Leyva-Parra
- Centro de Química Teórica & Computacional (CQT&C), Departamento de Ciencias Químicas, Facultad de Ciencias Exactas, Universidad Andrés Bello, Av. República 275, 8370146, Santiago, Chile
- Programa de Doctorado en Fisicoquímica Molecular, Facultad de Ciencias Exactas, Universidad Andrés Bello, Av. República 275, 8370146, Santiago, Chile
| | - Ricardo Pino-Rios
- Instituto de Estudios de la Salud, Universidad Arturo Prat, Iquique, 1100000, Chile
- Química y Farmacia, Facultad de Ciencias de la Salud, Universidad Arturo Prat, Casilla 121, Iquique, 1100000, Chile
| | - Diego Inostroza
- Centro de Química Teórica & Computacional (CQT&C), Departamento de Ciencias Químicas, Facultad de Ciencias Exactas, Universidad Andrés Bello, Av. República 275, 8370146, Santiago, Chile
- Programa de Doctorado en Fisicoquímica Molecular, Facultad de Ciencias Exactas, Universidad Andrés Bello, Av. República 275, 8370146, Santiago, Chile
| | - Miquel Solà
- Institute of Computational Chemistry and Catalysis, Departament of Chemistry, University of Girona, C/M Aurèlia Campmany 69, 17003, Girona, Catalonia, Spain
| | - Mercedes Alonso
- Departament of General Chemistry (ALGC), Vrije Universiteit Brussel, Pleinlaan 2, 1050, Brussels, Belgium
| | - William Tiznado
- Centro de Química Teórica & Computacional (CQT&C), Departamento de Ciencias Químicas, Facultad de Ciencias Exactas, Universidad Andrés Bello, Av. República 275, 8370146, Santiago, Chile
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Karadakov PB. How Different are the Diamagnetic and Paramagnetic Contributions to Off-Nucleus Shielding in Aromatic and Antiaromatic Rings? Chemphyschem 2023; 24:e202300038. [PMID: 36811600 DOI: 10.1002/cphc.202300038] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Revised: 02/15/2023] [Accepted: 02/21/2023] [Indexed: 02/24/2023]
Abstract
The spatial variations in the diamagnetic and paramagnetic contributions to the off-nucleus isotropic shielding, σ i s o r = σ i s o d r + σ i s o p r ${\ {{\sigma }_{{\rm i}{\rm s}{\rm o}}\left({\bf r}\right)=\ \sigma }_{{\rm i}{\rm s}{\rm o}}^{{\rm d}}\left({\bf r}\right)+{\sigma }_{{\rm i}{\rm s}{\rm o}}^{{\rm p}}\left({\bf r}\right)}$ , and to the zz component of the off-nucleus shielding tensor, σ z z r = σ z z d r + σ z z p r ${{{\sigma }_{zz}\left({\bf r}\right)=\sigma }_{zz}^{{\rm d}}\left({\bf r}\right)+{\sigma }_{zz}^{{\rm p}}\left({\bf r}\right)}$ , around benzene (C6 H6 ) and cyclobutadiene (C4 H4 ) are investigated using complete-active-space self-consistent field wavefunctions. Despite the substantial differences between σ i s o r ${{\sigma }_{{\rm i}{\rm s}{\rm o}}\left({\bf r}\right)}$ and σ z z r ${{\sigma }_{zz}\left({\bf r}\right)}$ around the aromatic C6 H6 and the antiaromatic C4 H4 , the diamagnetic and paramagnetic contributions to these quantities, σ i s o d r ${{\sigma }_{{\rm i}{\rm s}{\rm o}}^{{\rm d}}\left({\bf r}\right)}$ and σ z z d r ${{\sigma }_{zz}^{{\rm d}}\left({\bf r}\right)}$ , and σ i s o p r ${{\sigma }_{{\rm i}{\rm s}{\rm o}}^{{\rm p}}\left({\bf r}\right)}$ and σ z z P r ${{\sigma }_{zz}^{{\rm P}}\left({\bf r}\right)}$ , are found to behave similarly in the two molecules, shielding and deshielding, respectively, each ring and its surroundings. The different signs of the most popular aromaticity criterion, the nucleus-independent chemical shift (NICS), in C6 H6 and C4 H4 are shown to follow from a change in the balance between the respective diamagnetic and paramagnetic contributions. Thus, the different NICS values for antiaromatic and antiaromatic molecules cannot be attributed to differences in the ease of access to excited states only; differences in the electron density, which determines the overall bonding picture, also play an important role.
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Affiliation(s)
- Peter B Karadakov
- Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK
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Gutierrez VS, Arnault A, Ferreira V, Artigas A, Hagebaum-Reignier D, Carissan Y, Coquerel Y, Hiebel MA, Suzenet F. Synthesis, Photophysical Properties, and Aromaticity of Pyrazine-Fused Tetrazapentalenes. J Org Chem 2022; 87:13653-13662. [PMID: 36197438 DOI: 10.1021/acs.joc.2c01308] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Pyrazine-fused 1,2,6,6a-tetrazapentalenes (PyTeAP) are zwitterionic tricyclic compounds exhibiting an original pattern with four consecutive nitrogen atoms. They were obtained by a challenging cyclization through the formation of a N-N bond under thermolytic conditions. Ten derivatives were synthesized, and the original scaffold of PyTeAP was confirmed by single-crystal X-ray diffraction analysis of one derivative. Examination of their photophysical properties in solution revealed blue fluorescence with λem = 416-426 nm. Theoretical investigations of the aromaticity in these compounds through magnetic criteria evidenced the presence of a dominant 14-electron circuit at the periphery.
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Affiliation(s)
| | - Axel Arnault
- Université d'Orléans, CNRS, ICOA, UMR 7311,Orléans, France
| | | | - Albert Artigas
- Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France
| | | | - Yannick Carissan
- Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France
| | - Yoann Coquerel
- Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France
| | | | - Franck Suzenet
- Université d'Orléans, CNRS, ICOA, UMR 7311,Orléans, France
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