On Molecular Orbital Correlation Diagrams, the Occurrence of Möbius Systems in Cyclization Reactions, and Factors Controlling Ground- and Excited-State Reactions. I

Zimmerman, Howard E.

doi:10.1021/ja00959a052

Cited by 293 publications

(163 citation statements)

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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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“…The classical [4n+2] rule to rationalize aromaticity was first proposed by Erich Hückel in 1931 and was later developed by Doering 1,2 . In 1960s, Dewar gave the first explanation on Hückel's rule, which was later extended to Möbius topology by Heilbronner and Zimmerman but inverted [3][4][5][6] . The concept of ground-state aromaticity has been well developed and serves as a robust tool for rationalizing chemical reactions and properties 7,8 .…”

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Adaptive aromaticity in S0 and T1 states of pentalene incorporating 16 valence electron osmium

Chen

Shen

et al. 2018

Commun Chem

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Aromaticity is a fundamental chemical concept of ever-increasing diversity. According to Hückel's and Baird's rules, cyclic conjugated species with 4n+2 π-electrons are aromatic in the singlet electronic ground state (S 0 ) and antiaromatic in the lowest triplet state (T 1 ), and vice-versa. Thus, species with aromaticity in both states have not yet been reported. Here we carry out density functional theory calculations on recently synthesized organometallics, namely osmapentalyne and osmapentalenes, and demonstrate the first example (16-electron osmapentalene) of aromaticity in both S 0 and T 1 states, which we term adaptive aromaticity. Further electronic structure analysis reveals that the excitation pattern for the formation of the T 1 state plays a crucial role in the achievement of adaptive aromaticity. Our findings highlight the role of a transition metal in unorthodox excitation behavior, and may aid the design of adaptive aromatics for photochemical and molecular magnetism applications.

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On Molecular Orbital Correlation Diagrams, the Occurrence of Möbius Systems in Cyclization Reactions, and Factors Controlling Ground- and Excited-State Reactions. I

Abstract: for this spectrum. (4) Due to miscalibration, the nmr signals previously reported for this compound are in error; we now find a complex group of signals at S (CCI4) 1.5-2.3 ppm with three sharp signals at 0.93, 0.98, and 1.20 ppm.

Cited by 293 publications

References 1 publication

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

Adaptive aromaticity in S0 and T1 states of pentalene incorporating 16 valence electron osmium

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