Configuration Change in [14]Annulene Requires Möbius Antiaromatic Bond Shifting

Moll, Joseph; Pemberton, Ryan P.; Gutierrez, M. Gertrude; Castro, Claire; Karney, William L.

doi:10.1021/ja0678469

Cited by 43 publications

(37 citation statements)

References 24 publications

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“…As a consequence, Möbius aromaticity and antiaromaticity are defined respectively by a doubly even (4n) and singly even electron count (4n + 2). [11] Möbius aromaticity was subsequently invoked in several theoretical discussions, and proposed, sometimes controversially, as possible transition states [128][129][130] or reactive intermediates. [131] However, the first example of a stable, neutral Möbius molecule was experimentally characterized in 2003.…”

Section: Möbius Aromaticitymentioning

confidence: 99%

Figure Eights, Möbius Bands, and More: Conformation and Aromaticity of Porphyrinoids

2011

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The aromatic character of porphyrins, which has significant chemical and biological consequences, can be substantially altered by judicious modifications of the parent ring system. Expansion of the macrocycle, which is achieved by introducing additional subunits, usually increases the so-called free curvature of the ring, leading to larger angular strain. This strain is reduced by a variety of conformational changes, most notably by subunit inversion and p surface twisting. The latter effect creates a particularly convenient access to Möbius aromatic molecules, whose properties, predicted over 40 years ago, are of considerable theoretical importance. The conformational processes occurring in porphyrin analogues are often coupled to other chemical phenomena, and can thus be exploited as a means of constructing functional molecular devices. In this Review, the structural chemistry of porphyrinoids is discussed in the context of their conformational dynamics and p-electron conjugation.

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Section: Möbius Aromaticitymentioning

confidence: 99%

Figure Eights, Möbius Bands, and More: Conformation and Aromaticity of Porphyrinoids

2011

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“…einfach-gerade (4n + 2) Elektronenzählung definiert sein. [11] Verschiedene theoretische Arbeiten befassten sich später teilweise kontrovers mit der Möbius-Aromatizität und schlugen sie als möglichen Übergangszustand [128][129][130] oder reaktive Zwischenstufe [131] vor. Dann jedoch wurde 2003 das erste stabile, neutrale Möbius-Molekül charakterisiert, [87,92] ein Annulen-Bianthrochinondimethan-Hybrid, das eine kombinierte planare und In-plane-p-Konjugation aufweist (siehe Abbildung 3).…”

Section: Möbius-aromatizitätunclassified

Figure‐Eight‐Strukturen, Möbius‐Bänder und mehr: Konformation und Aromatizität von Porphyrinoiden

2011

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Der aromatische Charakter von Porphyrinen, der signifikante chemische und biologische Auswirkungen hat, kann durch gezielte Modifikationen des Stammringsystems beträchtlich verändert werden. Zusätzliche Untereinheiten expandieren den Makrocyclus und erhöhen seine Ringkrümmung, was zu einer höheren Winkelspannung führt. Diese Winkelspannung kann der Ring durch eine Reihe von Konformationsänderungen wieder abbauen, insbesondere durch Invertieren von Untereinheiten und Verdrillen (twisting) der π‐Oberfläche. Letzterer Effekt bietet einen Zugang zu Möbius‐aromatischen Molekülen, deren Eigenschaften, gleichwohl vor über 40 Jahren vorausgesagt, unter theoretischen Aspekten von großer Bedeutung sind. Häufig gehen Konformationsprozesse in den Porphyrinanaloga mit anderen chemischen Phänomenen einher, sodass sie für den Aufbau von molekularen Funktionseinheiten verwendet werden können. In diesem Aufsatz wird die Strukturchemie der Porphyrinoide im Zusammenhang mit ihrer Konformationsdynamik und elektronischen π‐Konjugation diskutiert.

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“…Since ∆ trans, i.e., the difference of trans double bonds between reactant and product, is 1, this means that one trans double bond isomerizes to cis. The reaction mechanism consists of three steps (see Figure 35) and requires in the final step a Möbius antiaromatic transition state [9].…”

Section: [14]annulenementioning

confidence: 99%

“…The reaction requires a Möbius bond shifting step and since [14]annulene is a (4n + 2) π-electron system the bond equalized transition state is antiaromatic, T S1 in Figure 35. The three step reaction CT CT CT T → CCT CT CT has an energy barrier in the bond shifting step of 19.3 kcal/mol [9]. Figure 34.…”

Section: [14]annulenementioning

confidence: 99%

“…For instance, benzene has represented along the years one of the preferred reference systems in order to validate new ab initio theoretical procedures. Higher annulenes, on the other hand, have allowed to investigate about isomeric rearrangements by means of advanced experimental techniques [6] and theoretical methods [7][8][9]. Comprehensive treatments of annulene preparation, structure and properties are available in textbooks [4,10,11], thematic issues [12,13] and review articles [14,15].…”

Section: Introductionmentioning

confidence: 99%

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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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Configuration Change in [14]Annulene Requires Möbius Antiaromatic Bond Shifting

Cited by 43 publications

References 24 publications

Figure Eights, Möbius Bands, and More: Conformation and Aromaticity of Porphyrinoids

Figure Eights, Möbius Bands, and More: Conformation and Aromaticity of Porphyrinoids

Figure‐Eight‐Strukturen, Möbius‐Bänder und mehr: Konformation und Aromatizität von Porphyrinoiden

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

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