Aromaticity and homoaromaticity of annulene ring carbomers

Lepetit, Christine; Godard, Cyril; Chauvin, Rémi

doi:10.1039/b009188j

Cited by 46 publications

(65 citation statements)

References 27 publications

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“…Figure 12 compares various aromaticity measures of [N]annulenes and their ring carbomers (N = 3-6) from optimized geometries at the B3PW91/6-31G** level [34,35]. The experimentally unknown carbo-cyclopentadienyl cation [16b] possesses virtually the same NICS and Breslow resonance energy (BRE) values as carbo-benzene.…”

Section: Carbo-[n]annulenic Species N ≠mentioning

confidence: 99%

“…This formula also holds for any dehydro[N]annulene as soon as the sp-sp and sp-sp 2 resonance integrals can be averaged. This was found to be possible for carbo-annulenes, since DFT and Hartree-Fock (HF) π-MO levels accurately vary as cos(2kπ/N) [34]. It was also incidentally observed that the extracted β values vary with the annulene size as: β = β ∞ N/(N + 2), where β ∞ = cste.…”

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confidence: 99%

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Ring carbo-mers: From questionable homoaromaticity to bench aromaticity

Zou

Lepetit

Coppel

et al. 2006

Pure and Applied Chemistry

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Abstract:The title journey is undertaken at the levels of both theory and experiment. Since 1983, homoaromaticity has been shown to play at most a minor role in the stability of Scott's [N]pericyclyne hydrocarbons-the first ring carbo-mers of cycloalkanes. This statement has been systematically refined for N = 3-6 by using both classical theoretical tools and newly designed tools based on electron localization function (ELF) analysis. The compatibility of the [5]-and [6]-pericyclyne cores with vertex functionalities was established by the synthesis of 20 oxy (carbo-cyclitol) derivatives. The stereoisomeric resolution of two of them has been achieved. pericyclynes are actually potential precursors of the carbo-benzenes. Criteria based on density functional theory (DFT) calculations (magnetic, energetic, structural/"electronic") show that the aromaticity of carbo- [N]annulenic species is comparable to that of their parent molecule. This has been challenged by the synthesis of several novel carbo-benzenic molecules with various substitution patterns. The theory-experiment interplay is pursued by considering ring carbo-mers of other conjugated ring systems such as radialenes. The second carbo-mers (butadiyndiyl-expanded rings) of [3]radialene and benzene are also envisioned. Hexaphenyl-carbo 2 -benzene has been observed by 1 H NMR and UV-vis spectroscopy.

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Section: Carbo-[n]annulenic Species N ≠mentioning

confidence: 99%

mentioning

confidence: 99%

Ring carbo-mers: From questionable homoaromaticity to bench aromaticity

Zou

Lepetit

Coppel

et al. 2006

Pure and Applied Chemistry

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“…For the sake of completeness we have included two non-aromatic seven and eight-membered rings molecules (C 7 H 14 and C 8 H 16 ), an aromatic seven-membered ring (C 7 H + 7 ) and hexaethynyl-carbo-benzene (C 18 H 6 ) as the molecule with a very large ring. 46 This gives a total of seventeen 6-MRs, three 7-MRs, four 8-MRs, one 9-MR, four 10-MRs and one 12-MR (total 30 points) that will be used to compare the performance of MCI and AV1245. In addition, there is four 14-MRs, one 16-MR and two 18-MRs data for which only AV1245 values will be provided.…”

Section: Computational Detailsmentioning

confidence: 99%

An electronic aromaticity index for large rings

Matito

2016

Phys. Chem. Chem. Phys.

134

139

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We introduce a new electronic aromaticity index, AV1245, consisting in the average of the 4-center MCI values along the ring that keep a positional relationship of 1,2,4,5. AV1245 measures the extent of transferability of the delocalized electrons between bonds 1-2 and 4-5, which is expected to be large in conjugated circuits and, therefore, in aromatic molecules. A new algorithm for the calculation of MCI for large rings is also introduced and used to produce the data for the calibration of the new aromaticity index. AV1245 does not rely on reference values, does not suffer from large numerical precision errors, and it does not present any limitation on the nature of atoms, the molecular geometry or the level of calculation. It is a size-extensive measure with a small computational cost that grows linearly with the number of ring members. Therefore, it is specially suitable to study the aromaticity of large molecular rings as those occurring in belt-shaped Möbius structures or porphyrins.

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“…[25] Ac losed-shells inglet ground state was reported for carbo-benzene, the ring carbo-mer of benzene. [26] In contrast to the above-described acyclic systems, the open-shell singlet state of thesem acrocyclesm ay be contaminated not only by the triplet spin state, but also by several higher multiplets up to the septets pin state. The sixth-order symmetry of the above-described macrocyclesa nd the NOON occupations significantly shiftedf rom 0o r2 ,a re suggesting that the septet could be the major contaminant and thus anatural candidate for spin decontamination by using method A.…”

Section: From Acyclic To Macrocyclic Molecular Magnetsmentioning

confidence: 98%

Towards Magnetic Carbo‐meric Molecular Materials

Poidevin

Malrieu

Trinquier

et al. 2016

Chemistry A European J

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Numerous studies have underlined the putative diradical character of π-conjugated molecules that can be described by closed-shell Lewis structures, for instance, p-dimethylene p-n phenylenes, or long polyacenes. In the latter compounds, the only way to save the aromaticity of the six-membered rings is to give up the Lewis electron pairing in the singlet biradical ground state. The present work considers the possibility of doing the same by using the basic C2 units of carbo-meric architectures. A series of acyclic and cyclic carbo-meric architectures is studied by using UB3LYP DFT broken-symmetry calculations, including spin decontaminations and subsequent geometry optimization of the singlet diradical. The C2 units are shown to stabilize the singlet biradical by spin delocalization, two of them playing approximately the same role as one radical-insulating 1,4 phenylene moiety. The results are generalized to the investigation of open-shell polyradical singlet states of rigid hydrocarbon structures, the symmetry and rigidity of which can assist cooperativity and self spin polarization effect. Several synthesis targets with challenging magnetic/spin properties are suggested in the carbo-mer series.

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Aromaticity and homoaromaticity of annulene ring carbomers

Cited by 46 publications

References 27 publications

Ring carbo-mers: From questionable homoaromaticity to bench aromaticity

Ring carbo-mers: From questionable homoaromaticity to bench aromaticity

An electronic aromaticity index for large rings

Towards Magnetic Carbo‐meric Molecular Materials

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