Highly Aromatic Planar <i>all</i>-<i>cis</i>-[10]Annulene Derivatives

Schleyer, Paul von Ragué; Jiao, Haijun; Sulzbach, Horst M.; Schaefer, Henry F.

doi:10.1021/ja953126i

Cited by 70 publications

(48 citation statements)

References 20 publications

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“…A strategy has been proposed [185] to generate planar [10]annulenes analogues of benzene where cyclopropene or cyclobutene units are fused with the D 10h ring. Density functional results indicate that derivatives with attached five cyclopropene or cyclobutene units arrange as planar D 5h structures that are local minima on the energy surface [185]. Introducing one alkyne moiety, 1,2-didehydro [10]annulene is formed, characterized by several conformational minima and transition states [186].…”

Section: [10]annulenementioning

confidence: 99%

Structures of Annulenes and Model Annulene Systems in the Ground and Lowest Excited States

Gellini

Salvi

2010

Symmetry

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The paper introduces general considerations on structural properties of aromatic, antiaromatic and non-aromatic conjugated systems in terms of potential energy along bond length alternation and distortion coordinates, taking as examples benzene, cyclobutadiene and cyclooctatetraene. Pentalene, formally derived from cyclooctatetraene by cross linking, is also considered as a typical antiaromatic system. The main interest is concerned with [n]annulenes and model [n]annulene molecular systems, n ranging from 10 to 18. The rich variety of conformational and configurational isomers and of dynamical processes among them is described. Specific attention is devoted to bridged [10]-and [14]annulenes in the ground and lowest excited states as well as to s-indacene and biphenylene. Experimental data obtained from vibrational and electronic spectroscopies are discussed and compared with ab initio calculation results. Finally, porphyrin, tetraoxaporphyrin dication and diprotonated porphyrin are presented as annulene structures adopting planar/non-planar geometries depending on the steric hindrance in the inner macrocycle ring. Radiative and non-radiative relaxation processes from excited state levels have been observed by means of time-resolved fluorescence and femtosecond transient absorption spectroscopy. A short account is also given of porphycene, the structural isomer of porphyrin, and of porphycene properties.

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Section: [10]annulenementioning

confidence: 99%

Structures of Annulenes and Model Annulene Systems in the Ground and Lowest Excited States

Gellini

Salvi

2010

Symmetry

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“…Such species could be investigated experimentally, as has been reported for the cyclooctatetraene derivative 5. [32] Like the small ring-fused cyclodecapentaenes 6, 7, [33] planar structures 8X also are predicted computationally here.…”

Section: Introductionmentioning

confidence: 54%

“…[33] Likewise, annelation of the CϭC bonds by three-membered rings results in planar nine-membered rings: 8CH 2 , 8O and 8S have planar minima with well equalized bond lengths. Furthermore, the planarization barrier of 8PH, 7.6 kcal/mol, is smaller than the 10.7 kcal/mol computed for 1PH (Table 1).…”

Section: Experimentally Realizable Planar Heteroninsmentioning

confidence: 99%

To What Extent Can Nine‐Membered Monocycles Be Aromatic?

2003

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Ab initio and density functional computations have been used to characterize the heteronins. New targets for synthesis are suggested on the basis of the results. The aromaticity of the heteronins was evaluated via numerous criteria such as magnetic properties (NICS and δH), geometric indices (Bird, BDSHRT and HOMA), aromatic stabilization energies (ASE), and the barriers to planarity. Along with the experimentally characterized cyclononatetraenyl (1CH−) and azonide (1N−) anions, the phosphonide ion (1P−, which has not been reported before), favors planar (C2v) symmetry. All the other heteronins are nonplanar in order to alleviate ring strain. Comparisons of the neutral planar heteronins (constrained to C2v symmetry) show the extent to which heteroatoms like P and S, as well as N and O (in oxonin, 1O), can participate in the cyclic electron delocalization. Due to hyperconjugation, the C2v‐symmetric 9,9‐distannylcyclononatetraene 1C(SnH3)2 is moderately aromatic, in contrast to 1CH2, which is a nonaromatic, conjugated system. The planar C2v‐symmetric 1BH and 1AlH and 1CF2 are antiaromatic, like the planar form of 1CH+. Annelation with three‐membered rings resulted in planar heteronins. The sole exception was phosphonin (8PH), but the barrier to planarity decreased to 1.8 kcal/mol in 8PR, due to the bulky R: 2,6‐di‐tert‐butylphenyl substituent at the phosphorus atom. Among the 8π heteronins, only the previously reported 1CH+ is Möbius‐aromatic; 1BH, 1AlH and 1CF2 also have C2 structures but are nonaromatic due to large torsional angles which preclude cyclic delocalization. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

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“…Generally, as recommended [31], the present study employs geometries obtained from standard MNDO [32] calculations, which have been optimized within the same point group as in the reference ab initio and density functional studies [3][4][5][6][7][8][9][10][11][12]. The differences between the MNDO and the reference geometries will cause some of the observed deviations between the corresponding NICS values.…”

Section: Methodsmentioning

confidence: 99%

“…In a few rare cases, however, these differences were large enough to necessitate the use of constrained geometries (details see below). Table 1 compares the NICS values from GIAO-MNDO with those from published ab initio and density functional studies [3][4][5][6][7][8][9][10][11][12]. Figure 1 shows a corresponding correlation plot, and Table 2 presents a statistical evaluation of the data.…”

Section: Methodsmentioning

confidence: 99%

Nucleus-Independent Chemical Shifts from Semiempirical Calculations

Patchkovskii

Thiel

2000

J Mol Model

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A recently developed special MNDO parameterization for NMR chemical shifts is used to compute the nucleus-independent chemical shifts (NICS) for a wide range of organic molecules, including [n]annulenes, polycyclic hydrocarbons, heterocycles, cage molecules, fullerenes, and pericyclic transition states. The results are compared with published NICS data from ab initio and density functional calculations. In general, there is reasonable agreement. The semiempirical NICS values tend to be smaller in absolute value than their ab initio counterparts, but they often show similar trends. The aromatic or antiaromatic character of a given system can normally be assigned correctly on the basis of the MNDO NICS values

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Highly Aromatic Planar all-cis-[10]Annulene Derivatives

Cited by 70 publications

References 20 publications

Structures of Annulenes and Model Annulene Systems in the Ground and Lowest Excited States

Structures of Annulenes and Model Annulene Systems in the Ground and Lowest Excited States

To What Extent Can Nine‐Membered Monocycles Be Aromatic?

Nucleus-Independent Chemical Shifts from Semiempirical Calculations

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