Zur Konjugation in makrocyclischen Bindungssystemen [1] XX. Charakterordnung, magnetische Suszeptibilit�ten und chemische Verschiebungen von Corannulenen

Ege, Günter; Vogler, Helmut

doi:10.1007/bf00527653

Cited by 45 publications

(33 citation statements)

References 19 publications

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“…The last row for each ring is the sum of bond orders for the ring and represents a "C=C deficiency" measure for the ring, the value of 3.000 characterizing the benzene ring. @ @ @ (4,4,4) (222R2, + 156R2 + 96R3 + 2Q3)/54 4.464 0.124 0.496 (2,4,2,4) (300R, + 192R2 + 138R3)/68 4.625 0.116 0.462 (3,4,3,4) Finally in Table V we list ring characters for all symmetry unrelated rings in molecules of Figure 1 . As we see from the entries in Table V none of the rings shows visible similarity to the benzene ring.…”

Section: Resultsmentioning

confidence: 99%

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Conjugation and aromaticity of macrocyclic systems

Randić

Henderson

Stout

et al. 1988

Int. J. Quantum Chem.

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Using a graph theoretical approach we have analyzed the aromatic stability of macrocyclic systems having ten and fewer fused benzene rings. The approach requires construction and examination of Kekule valence structures of the macrocyclic systems considered. The Kekule valence structures for a molecule were systematically derived and the conjugated circuits in the individual Kekule formulas were enumerated subsequently. The counting results is the expression for molecular resonance energy, from which relative aromatic stabilities can be established. We report also on molecular local features, including ring benzene characters and Pauling bond orders.

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Section: Resultsmentioning

confidence: 99%

“…We use numbers of CC bonds between neighboring CH atomic groups as the basis for the names. Thus we obtain the codes: ( 5 , 5 ) ; (4,4,4); (1,5,3,5); (2,5,2,5); and (3,4,3,4) for the five structures of Figure 1. The NPAC names for these compounds (as illustrated in Table I) are cumbersome, to say the least.…”

Section: Introductionmentioning

confidence: 99%

Conjugation and aromaticity of macrocyclic systems

Randić

Henderson

Stout

et al. 1988

Int. J. Quantum Chem.

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“…We wish to conclude this section by some remarks on py~ene and eo~onene, which both have been reckoned among eokannutene6 (Ege and Vogler 1972a;1972b;Vogler 1980). Figure 4 shows how two forms of the dualist (or a dualist-like figure) can distinguish between say [4]~eutene and py~ene on one hand, as well as (6]~ eutene and eo~onene on the other.…”

Section: The Story Of Kekulenementioning

confidence: 98%

Theory of Coronoid Hydrocarbons

Cyvín

Brunvoll

Cyvin

1991

Lecture Notes in Chemistry

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“…[6] The aim is to find p systems based on a circulene-like template, but with conrotating paratropic currents on both outer and inner cycles of carbon atoms. For annular belts of hexagonal rings, it has been shown [1,7] that coupling of inner and outer circuits leads to counterrotation of ring currents. A belt of 2m fused pentagons around a central 2m-gon, as in the case of 1, has four KekulØ structures corresponding to the pairings of the two conjugated structures on rim and hub cycles.…”

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Designing Paramagnetic Circulenes

et al. 2007

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In an axial magnetic field, the annular molecules coronene, corannulene, kekulene, and nonplanar [7]circulene support disjoint, counterrotating, diatropic-rim/paratropic-hub ring currents. [1] This remarkable feature represents a failure of the very popular "annulene within an annulene" (AWA) model. [2] On the other hand, a circulene comprising 10 fused pentagons around a central decagon, namely [10,5]coronene (1), is predicted to have inverted counterrotating paratropic-rim/ diatropic-hub ring currents. [3] In this case, the outer and inner cycles, which contain respectively 20 (4n) and 10 (4n + 2) carbon atoms, are essentially decoupled and here the AWA picture is compatible with the ab initio result. For all these systems, the ipsocentric approach [4] provides a unified account of the opposed currents in terms of simultaneous translational and rotational p-p* virtual excitations, and so provides a basis for further prediction and possible control of magnetic response properties in potential materials applications. For example, extensive paratropic (antiaromatic) perimeter circulation is an unusual property that is reflected in calculated magnetizability and nuclear magnetic shieldings, even when partially cancelled by the effects of a central diatropic current, as in 1.[3] Can we eliminate the cancellation and achieve greater paratropicity by reversing the central current? Here we predict that two closed-shell neutral circulenes, 2 and 3, support disjoint conrotating paratropic ring currents on both rim and hub. Indeed, the calculations indicate that 2 and 3 have a net paramagnetic response in one direction, and that in 3, remarkably, this outweighs the diamagnetic contributions to magnetizability to give a closed-shell paramagnetic molecule. Retention of paratropic current at equilibrium geometry is rare, and the received wisdom is that antiaromatic molecules will exhibit fluxionality [5] or distort to "escape" their antiaromaticity. [6] The aim is to find p systems based on a circulene-like template, but with conrotating paratropic currents on both outer and inner cycles of carbon atoms. For annular belts of hexagonal rings, it has been shown [1,7] that coupling of inner and outer circuits leads to counterrotation of ring currents. A belt of 2m fused pentagons around a central 2m-gon, as in the case of 1, has four KekulØ structures corresponding to the pairings of the two conjugated structures on rim and hub cycles. In all four, the radial 5/5 graph edges are formal single bonds and hence have zero Pauling p bond order. Thus, inner and outer circuits are decoupled, and this suggests that the AWA picture is applicable to this electronic structure. When 2m = 4n, the inner cycle should be antiaromatic; the outer 4m cycle should always be antiaromatic, independent of m. Two series of molecules can be postulated: one with 2m = 4n + 2, for which the AWA picture predicts counterrotating (paratropic-rim/diatropic-hub) ring currents, as in the case of 1, and a second with 2m = 4n, for which AWA would predict the des...

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Zur Konjugation in makrocyclischen Bindungssystemen [1] XX. Charakterordnung, magnetische Suszeptibilit�ten und chemische Verschiebungen von Corannulenen

Cited by 45 publications

References 19 publications

Conjugation and aromaticity of macrocyclic systems

Conjugation and aromaticity of macrocyclic systems

Theory of Coronoid Hydrocarbons

Designing Paramagnetic Circulenes

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