Are Oxocarbon Dianions Aromatic?

Schleyer, Paul von Ragué; Najafian, Katayoun; Kiran, Boggavarapu; Jiao, Haijun

doi:10.1021/jo991267n

Cited by 135 publications

(111 citation statements)

References 77 publications

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“…Aromaticity and coordination properties of this family have been investigated widely. 29,30 Squarate is a well-known member due to its unique electronic properties, vibration characteristics, and the simplicity of its cyclic species. A substantial degree of π -electron delocalization exists over the aromatic nucleus of squarate.…”

Section: Introductionmentioning

confidence: 99%

Compression studies of face-to-face π-stacking interaction in sodium squarate salts: Na2C4O4 and Na2C4O4•3H2O

Wang

et al. 2012

The Journal of Chemical Physics

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High-pressure Raman scattering and synchrotron X-ray diffraction measurements of sodium squarate (Na(2)C(4)O(4), SS) are performed in a diamond anvil cell. SS possesses a rare, but typical structure, which can show the effect of face-to-face π-stacking without interference of other interactions. At ~11 GPa, it undergoes a phase transition, identified as a symmetry transformation from P2(1)/c to P2(1). From high-pressure Raman patterns and the calculated model of SS, it can be proved that the phase transition results from the distorted squarate rings. We infer it is the enhancement of π-stacking that dominates the distortion. For comparison, high-pressure Raman spectra of sodium squarate trihydrate (Na(2)C(4)O(4)●3H(2)O, SST) are also investigated. The structure of SST is determined by both face-to-face π-stacking and hydrogen bonding. SST can be regarded as a deformation of SS. A phase transition, with the similar mechanism as SS, is observed at ~10.3 GPa. Our results can be well supported by the previous high-pressure studies of ammonium squarate ((NH(4))(2)C(4)O(4), AS), and vice versa. High-pressure behaviors of the noncovalent interactions in SS, SST, and AS are compared to show the impacts of hydrogen bonding and the role of electrostatic interaction in releasing process.

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Section: Introductionmentioning

confidence: 99%

Compression studies of face-to-face π-stacking interaction in sodium squarate salts: Na2C4O4 and Na2C4O4•3H2O

Wang

et al. 2012

The Journal of Chemical Physics

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“…In this index, the NICS value of studied molecule is computed as the negative magnetic shielding at some selected point in space, e.g. at a ring or cage center, 0.5 Å [19], 0.6 Å [20], 0.8 Å [21], 1.0 Å [22], and etc, above the plane of the rings. Comparing with other criteria, NICS does not require reference standards, increment schemes and calibrating (homodesmic) equations for evaluation; and more important, in several sets of related molecules, NICS correlates well with other aromaticity indexes based on geometric, energetic, and other magnetic criteria [23].…”

Section: Introductionmentioning

confidence: 99%

Using three major criteria to evaluate aromaticity of five-member C-containing rings and their Si-, N-, and P-substituted aromatic heterocyclics

Wang

Dong

et al. 2006

Struct Chem

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In this paper, we used bond-length equalization, aromatic stabilization energies (ASE) and nucleusindependent chemical shifts (NICS), calculated with (density functional theory) B3LYP levels at the 6-311 + G * * basis set, to evaluate the aromaticity of a set of 38 five-member planar π -electron aromatic systems: sila-, aza-and phosphaderivatives and their parent systems. The result revealed statistically significant correlations among the above three criteria, and the order of aromaticity of the whole set was: Aza-derivatives rings > Phospha-derivatives rings > Siladerivatives rings > Carbon-containing rings; NICS(0.6) and NICS(0.8) had the same results in evaluating the order of aromaticity in our case.

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“…The use of oxocarbons in organic chemistry synthesis is well known. 1 Crystalline structure of their hydrated alkali metals salts has been determined by X-ray measurements. 2 -4 Ab initio quantum chemistry calculations have been used in quantifying aromaticity in oxocarbon species.…”

Section: Introductionmentioning

confidence: 99%

Vibrational dephasing of the croconate dianion in different environments

Cavalcante

Ribeiro

2005

J. Raman Spectrosc.

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Raman band-shape analysis of croconate dianion, C 5 O 5 2− , was performed in order to reveal the short-time dynamics of this species in different environments: aqueous solution, acetonitrile solution, and the lowtemperature molten salt tetra(n-butyl)ammonium croconate, [(n-C 4 H 9 ) 4 N] 2 C 5 O 5 ·4H 2 O, TBCR. Two totally symmetric normal modes were investigated, the C-O stretching, n 1 , and the ring breathing, n 2 . Vibrational dephasing parameters for n 1 and n 2 display very different behaviour on changing the environment in which the C 5 O 5 2− moiety is located. A quantitative explanation of the changes in parameters is not yet available, but it is argued that strong hydrogen bond with water molecules is the origin of the very different dephasing dynamics of C 5 O 5 2− in aqueous solution in comparison with acetonitrile solution and TBCR. Thus, experimental vibrational time correlation functions nicely illustrate distinct sensitivity of different intramolecular oscillators of the solute to intermolecular dynamics, that is, distinct coupling between intra-and intermolecular degrees of freedom.

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Are Oxocarbon Dianions Aromatic?

Cited by 135 publications

References 77 publications

Compression studies of face-to-face π-stacking interaction in sodium squarate salts: Na2C4O4 and Na2C4O4•3H2O

Compression studies of face-to-face π-stacking interaction in sodium squarate salts: Na2C4O4 and Na2C4O4•3H2O

Using three major criteria to evaluate aromaticity of five-member C-containing rings and their Si-, N-, and P-substituted aromatic heterocyclics

Vibrational dephasing of the croconate dianion in different environments

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