Effect of nonplanarity in bridged [14]annulenes on the electron spin resonance spectra of their radical anions

Gerson, Fabian; Muellen, K.; Vogel, E.

doi:10.1021/ja00764a004

Cited by 37 publications

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“…Such a situation is, indeed, encountered in the [ 14lannulene 4. The observed sequence of the molecular orbitals can thereby be understood on the basis of a simple perturbation model [26]. This straightforward argument is not valid in 3-since the two lowest-lying HMO's exhibit a nodal plane through the ring atoms C (1) and C (8).…”

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confidence: 99%

The Dianions of Pyrene and Pyrene Isomers as (4n)π‐Perimeters

Müllen¹

1978

Helvetica Chimica Acta

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~~ SummaryMetal reduction of pyrene and of pyrene isomers under carefully controlled conditions yields the corresponding dianions. The properties of the neutral compounds and of the dianions are studied via 'H-NMR. spectroscopy. Whereas the former exhibit similar behaviour, the charge distribution within the dianionic species proves to be very different. As a consequence, some of the polycyclic dianions can be regarded essentially as (4n)~-perimeters, an approach which is satisfactorily rationalized by simple MO-models. Further evidence in favour of this bonding scheme comes from the ESR. spectroscopic measurement of the spin density distribution within the corresponding radical anions.1. Introduction. -Due to the simple topology of annulenes their eigenvalues within a HMO-model can be determined in a closed form [l]. It is well known that the resulting orbital patterns exhibit certain regularities which allow a straightforward interpretation of various spectroscopic properties [2]. Thus, as the annulenes constitute suitable probes for the ascertainment of theoretical predictions [l] [2] it is not surprising that they also have been invoked as model compounds for more complicated rr-species. Typical examples are represented by the transition states of electrocyclic rearrangements [3] or by unsaturated polycycles.When depicting the possible KekulP-structures for an unsaturated polycycle one can well raise the question whether perimeter-type structures contribute to the ground-state of the molecule. Various molecular properties have been referred to in order to estimate the importance of perimeter structures in polycycles. The charge distribution, e.g. within porphyrin systems, which represent potential [ 181annulenes [4] [5], has been determined from 13C-chemical shifts and from MO-calculations or characteristic ring current effects have been evaluated from 'H-NMR. data in corannulenes [6] and annuleno-annulenes [7].The spectroscopic characterization of n-systems does not necessarily provide a clear-cut conclusion about the specific bonding situations. This short-coming can in part be attributed to the fact that the resulting data depend on geometrical factors such as the configuration or conformation of the rings. However, when transforming

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The Dianions of Pyrene and Pyrene Isomers as (4n)π‐Perimeters

Müllen¹

1978

Helvetica Chimica Acta

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“…Typical examples of [n]annulene derivatives with n obeying the Huckel rule of stability are l,6-methano [10]annulene (9), 1,6:8,13-bridged [14]annulenes 10 and 11, 10a,10b-dimethyl-10a,10b-dihydropyrene (12), and bisdehydro[n]annulenes with n = 14,18,22, and 26 (13). The radical ions of alkyl-substituted benzenes (16,23,26,65,111,119) and of [n]annulene derivatives (23,38,61,64,118,(120)(121)(122)(123) have been extensively studied by EPR spectroscopy since 1958 (16) and 1964 (38), respectively.…”

Section: Moderate Electron Acceptors and Donorsmentioning

confidence: 99%

“…In turn, the effect of the perturbation can be determined, which for alkylbenzenes and bridged [n]annulenes is usually classified as inductive, homoconjugative, and/or hyperconjugative. Interestingly, the radical cations of the diimino-bridged [14]annulenes (11) are N-centered, with a three-electron N-N o-bond (for m>3, % = 1.7-2.6 mT) (64), while in the corresponding anions (a N < 0.1 mT), as in both radical ions of 10, the spin population is almost entirely accommodated in the nperimeter (61,121). For the radical anions of 9-11, the coupling constants of the protons at the perimeter are strongly affected by deviations of the latter from planarity and can serve as a measure of such deviations (121).…”

Section: Moderate Electron Acceptors and Donorsmentioning

confidence: 99%

“…Interestingly, the radical cations of the diimino-bridged [14]annulenes (11) are N-centered, with a three-electron N-N o-bond (for m>3, % = 1.7-2.6 mT) (64), while in the corresponding anions (a N < 0.1 mT), as in both radical ions of 10, the spin population is almost entirely accommodated in the nperimeter (61,121). For the radical anions of 9-11, the coupling constants of the protons at the perimeter are strongly affected by deviations of the latter from planarity and can serve as a measure of such deviations (121). Structurally related to annulenes is porphyrin, of which some novel isomers and derivatives were recently converted to radical ions (124,125).…”

Section: Moderate Electron Acceptors and Donorsmentioning

confidence: 99%

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Organic Radical Ions as Studied by Epr Spectroscopy

Gerson¹

1998

Foundations of Modern EPR

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“…Deviations of the p-system from planarity are known to decrease the |a H | value of the proton attached to a p-center because they provide positive contributions to the negative coupling constant of such a proton. 10,11 On the other hand, the symmetry of 1 •2 may be lower owing to Jahn-Teller distortion, modifying the coupling constant.…”

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confidence: 99%