The .nu.14(b2u) Mode of Benzene in S0 and S1 and the Distortive Nature of the .pi. Electron System: Theory and Experiment

Haas, Yehuda; Zilberg, Shmuel

doi:10.1021/ja00124a033

Cited by 73 publications

(69 citation statements)

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“…31 Berry 32 used this suggestion to account for the observed increased frequency of the b2u Kekule vibrational mode when going from the ground 1 A1g to the first 1 B2u excited state. The same idea was reinforced later on by the work of Haas and Zilberg, 33,34 and especially by that of Hiberty, Shaik, and co-workers 35,36 and others 37,38 Finally, more recently Pierrefixe and Bickelhaupt [39][40][41] showed that the regular geometry of benzene is a consequence of how  and overlaps depend on bond distances. In aromatic annulenes the authors confirmed that bond equalisation is due to the  electrons whereas the -electron system favours doublebond localisation.…”

Section: Introductionmentioning

confidence: 88%

Quantifying aromaticity with electron delocalisation measures

et al. 2015

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Aromaticity cannot be measured directly by any physical or chemical experiment because it is not a well-defined magnitude. Its quantification is done indirectly from the measure of different properties that are usually found in aromatic compounds such as bond length equalisation, energetic stabilisation, and particular magnetic behaviour associated with induced ring currents. These properties have been used to set up the myriad of structural-, energetic-and magnetic-based indices of aromaticity known to date. Cyclic delocalisation of mobile electrons in two or three dimensions is probably one of the key aspects that characterise aromatic compounds. However, it has not been until the last decade that electron delocalisation measures have been widely employed to quantify aromaticity. Some of these new indicators of aromaticity such as the PDI, FLU, ING, and INB were defined in our group. In this paper, we review the different existent descriptors of aromaticity that are based on electron delocalisation properties, we compare their performance with indices based on other properties, and we summarise a number of applications of electronic-based indices for the analysis of aromaticity in interesting chemical problems.2

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Section: Introductionmentioning

confidence: 88%

Quantifying aromaticity with electron delocalisation measures

et al. 2015

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“…6,8,13,15 After the synthesis of [N]phenylenes of various topologies, [16][17][18][19][20][21][22][23][24][25][26][27][28] the experimental confirmation of the theoretical data has become possible. The cyclohexatriene nature of the central ring of (1) in the ground state has been demonstrated experimentally by the chemical reactivity of this compound 29,30 and the X-ray diffraction data. 19 31 Therefore, an analysis of the vibronic structure of the fluorescence and absorption spectra of [N]phenylenes is necessary.…”

Section: Introductionmentioning

confidence: 91%

“…Indeed, the calculated NICS values and π-ring current maps for (1) suggest that the central ring is not aromatic by these criteria. 6,8,13,15 After the synthesis of [N]phenylenes of various topologies, [16][17][18][19][20][21][22][23][24][25][26][27][28] the experimental confirmation of the theoretical data has become possible.…”

Section: Introductionmentioning

confidence: 96%

“…1 One explanation for the abnormal shift of this vibration to higher energies in the S 1 -state was the concept of the excited twin state introduced by Shaik. [2][3][4][5] This model suggested that the delocalization of the CC-bonds in benzene is enforced by the σ-system, whereas the π-system tends to adopt a localized structure.…”

Section: Introductionmentioning

confidence: 99%

“…If the π-bond length is enlarged in an alternating manner, as in the angular [N]phenylenes, the central six-membered ring will be deformed in a cyclohexatriene-type way, with the effect being maximal for (1). As a result of the influence of the cyclobutadienoid rings, the aromatic character of the central ring changes to a non aromatic system, which can be measured in terms of NMR-shifts or vibrational energies.…”

Section: Introductionmentioning

confidence: 99%

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Deuteration effects on the vibronic structure of the fluorescence spectra and the internal conversion rates of triangular [4]phenylene

Dosche

Kumke

Löhmannsröben

et al. 2004

Phys. Chem. Chem. Phys.

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The electron-pair origin of antiaromaticity: Spectroscopic manifestations

Zilberg

Haas

1999

Int. J. Quant. Chem.

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ABSTRACT:It is shown that the antiaromatic character of certain conjugated cyclic hydrocarbons is due to the presence of an even number of distinct electron pairs in the Ž . system such as, but not necessarily electrons . In these systems, the ground state is Ž . constructed from an out-of-phase combination of two valence bond VB structures, and its equilibrium geometry is necessarily distorted along the coordinate that interchanges these structures. If a new symmetry element appears during the transition between the two structures, the ground electronic state at the symmetric point transforms as one of the nontotally symmetric irreducible representations of the point group. The conjugate excited state, formed from the in-phase combination of the same two structures, transforms as the totally symmetric representation of the group and is strongly bound. Its structure is similar to that of the ground state at the symmetric point, and the energy separation between the two states is small compared to that of conjugated cyclic hydrocarbons having an odd number of distinct electron pairs. Motion along the ''Kekule-type'' vibrational mode on the excited-state potential surface is very similar tó motion along the reaction coordinate connecting the two distorted structures on the ground-state surface. It is characterized by a significantly higher vibrational frequency compared to frequencies of similar modes in ground-state molecules. These qualitative predictions are supported by quantum chemical calculations on cyclobutadiene, cyclooctatetraene, and pentalene.

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The .nu.14(b2u) Mode of Benzene in S0 and S1 and the Distortive Nature of the .pi. Electron System: Theory and Experiment

Cited by 73 publications

References 2 publications

Quantifying aromaticity with electron delocalisation measures

Quantifying aromaticity with electron delocalisation measures

Deuteration effects on the vibronic structure of the fluorescence spectra and the internal conversion rates of triangular [4]phenylene

The electron-pair origin of antiaromaticity: Spectroscopic manifestations

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