An sp-hybridized all-carboatomic ring, cyclo[18]carbon: Bonding character, electron delocalization, and aromaticity

Liu, Zeyu; Tian, Laijin; Chen, Qinxue

doi:10.1016/j.carbon.2020.04.099

Cited by 226 publications

(274 citation statements)

References 58 publications

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“…For cyclo[18]carbon, the two delocalized donut-like π-electron systems contain 18π electrons each. 5 , 7 , 10 , 25 The two π-electron systems are not identical because the p in orbitals on the outside of the ring have a slightly smaller overlap than the p out orbitals because of the bent curvature of the ring.…”

Section: Introductionmentioning

confidence: 99%

Aromaticity of Even-Number Cyclo[n]carbons (n = 6–100)

et al. 2020

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The recently synthesized cyclo[18]carbon molecule has been characterized in a number of studies by calculating electronic, spectroscopic, and mechanical properties. However, cyclo[18]carbon is only one member of the class of cyclo[ n ]carbons—standalone carbon allotrope representatives. Many of the larger members of this class of molecules have not been thoroughly investigated. In this work, we calculate the magnetically induced current density of cyclo[ n ]carbons in order to elucidate how electron delocalization and aromatic properties change with the size of the molecular ring ( n ), where n is an even number between 6 and 100. We find that the Hückel rules for aromaticity (4 k + 2) and antiaromaticity (4 k ) become degenerate for large C n rings ( n > 50), which can be understood as a transition from a delocalized electronic structure to a nonaromatic structure with localized current density fluxes in the triple bonds. Actually, the calculations suggest that cyclo[ n ]carbons with n > 50 are nonaromatic cyclic polyalkynes. The influence of the amount of nonlocal exchange and the asymptotic behavior of the exchange–correlation potential of the employed density functionals on the strength of the magnetically induced ring current and the aromatic character of the large cyclo[ n ]carbons is also discussed.

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Section: Introductionmentioning

confidence: 99%

Aromaticity of Even-Number Cyclo[n]carbons (n = 6–100)

et al. 2020

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“…The geometric fluctuation of the cyclo[18]carbon must be accompanied by the change of its C−C bond lengths. Figure 11 displays the variations of all bonds of the cyclo[18]carbon during the AIMD simulation at 298.15 K. It is well known that the cyclo[18]carbon contains two kinds of C−C bonds of different lengths connected alternately [21,29] . Although the vibrations of both kinds of bonds are significant, no self‐exchange behavior is observed throughout the simulation period.…”

Section: Resultsmentioning

confidence: 99%

“…Unless otherwise specified, geometry optimizations, harmonic frequency analyses as well as evaluations of IR intensities and Raman activities for various cyclocarbons were all conducted using ωB97XD exchange‐correlation functional [52] in conjunction with def2‐TZVP basis set [53] by Gaussian 16 (A.03) program [54] . We have demonstrated that this calculation level is able to reasonably represent geometric and electronic structures of the cyclo[18]carbon [29–31] . No imaginary frequency was found for the optimized structures.…”

Section: Computational Sectionmentioning

confidence: 96%

“…With the confirmation of experimental evidence, a lot of theoretical efforts have been made to study properties of the cyclo[18]carbon from many aspects, including tunneling effect, [22] electron transfer, [23,24] surface coupling, [25] and so on [26–28] . Lately, we have also carried out a series of theoretical investigations on electron delocalization, aromaticity, electronic spectrum, optical nonlinearity, and intermolecular interaction of the cyclo[18]carbon [29–31] …”

Section: Introductionmentioning

confidence: 99%

“…Considering that experimental IR and Raman spectra are currently not available for the cyclo[18]carbon, theoretical spectra simulated by quantum chemistry calculation must be able to provide a useful guidance for chemists. Therefore, continuing our interest in the study of cyclic molecules with special topology [33–36] and as part of our comprehensive theoretical prediction of various properties of the cyclo[18]carbon, [29–31] we present a careful characterization of vibrational spectra for the cyclo[18]carbon in this paper. Furthermore, in view of other cyclic oligomers such as C 12 Br 4 and C 24 Br 8 were also detected in the debromination reaction mixture, the properties of other kinds of cyclocarbons are not only interesting in theory, but also very important in practical research.…”

Section: Introductionmentioning

confidence: 99%

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Vibrational Spectra and Molecular Vibrational Behaviors of All‐Carboatomic Rings, cyclo[18]carbon and Its Analogues

Liu

Tian²,

Chen³

2020

Chemistry An Asian Journal

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The vibrational spectra of cyclo[18]carbon and its analogues, cyclo[2n]carbon (n=3 to 15), were carefully simulated and characterized. The in‐plane C−C stretching vibrations shows strong rigidity, while out‐of‐plane motions seem to be extremely flexible. The solvation effect can enhance signal strengths of the vibrational spectra, but does not evidently change the shape of the spectral curves. The infrared and Raman spectra of cyclo[2n]carbons are quite sensitive to ring size in the range of n=3 to 7, while the size only modestly affects peak positions and strengths for larger rings. Molecular dynamic trajectories show that the fluctuation period of the skeleton of cyclo[18]carbon is basically constant at different temperatures, and they are all about 300 fs. With increase of simulation temperature, the ring distortion due to thermal motion is notable and becomes much stronger. However, neither ring breaking nor isomerization in cyclo[18]carbon is observed during the simulations untill 298.15 K.

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Realization of Conceptual Density Functional Theory and Information‐Theoretic Approach in Multiwfn Program

Tian¹,

Chen²

2022

Conceptual Density Functional Theory

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An sp-hybridized all-carboatomic ring, cyclo[18]carbon: Bonding character, electron delocalization, and aromaticity

Cited by 226 publications

References 58 publications

Aromaticity of Even-Number Cyclo[n]carbons (n = 6–100)

Aromaticity of Even-Number Cyclo[n]carbons (n = 6–100)

Vibrational Spectra and Molecular Vibrational Behaviors of All‐Carboatomic Rings, cyclo[18]carbon and Its Analogues

Realization of Conceptual Density Functional Theory and Information‐Theoretic Approach in Multiwfn Program

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