Concerning the Stability of Some Substituted Cyclopropenyl Radicals; Evidence From Polarography of the Corresponding Cations

Breslow, Ronald; Bahary, W. S.; Reinmuth, W. H.

doi:10.1021/ja01468a051

Cited by 41 publications

(15 citation statements)

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“…Thus we went to faster methods where we could observe both the reduction process and the subsequent oxidation of radicals back to cations, giving better values for the true energy costs of reduction. [25] Then we went to even faster methods, and were able to see the reversible reduction of simple cyclopropenyl cation to the corresponding radical and then to the carbanion. [26] The new technique was second harmonic ac voltammetry, with a simple concept.…”

Section: Aromaticitymentioning

confidence: 99%

“…Guided by the electrochemical expertise of my Columbia colleague William Reinmuth, we have used electrochemistry to investigate the properties of cyclopropenyl radicals and anions, specifically the energies required to add the needed electrons to the cations. In our first study co‐authored with Reinmuth we at first used simple polarography to reduce various cyclopropenyl cations to the radicals, but the subsequent coupling of the radicals was very fast, and this disturbed any equilibrium between cation and radical so the potentials observed were not true thermodynamic values. The relevant reducing potential is that which produces an equal concentration of starting material and product.…”

Section: Antiaromaticitymentioning

confidence: 99%

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Novel Aromatic and Antiaromatic Systems

Breslow

2014

The Chemical Record

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Note from the Editor: August Kekulé's dream and his theory of the structure of benzene (1865). Julius Thomsen's logic that benzene contains equivalent electrons between its carbon atoms (ca. 1900). Richard Willstätter's synthesis and observation that 1,3,5,7‐cyclooctatetraene is not aromatic (early 1900s). Sir Robert Robinson's proposal of the ‘aromatic sextet’ (1925). Erich Hückel's molecular orbital treatment of benzene and other unsaturated compounds that separated sigma and pi electrons (early 1930s). Tetsuo Nozoe and Michael Dewar's independent proposal of a new aromatic structure for a cycloheptatrieneone (mid‐1940s). Ronald Breslow's demonstration that cyclopropenyl cation is aromatic (1958). Breslow's proposal of ‘antiaromaticity’ (1965). I offer several comments. First, in the field of aromaticity, Breslow is in mighty exceptional company. Second, his research has extended well beyond aromaticity. Yes, Breslow is applying the concepts of antiaromaticity toward the development of highly conductive organic materials. But his research has encompassed enzyme mimics, remote functionalization reactions, unnatural DNA analogues and cancer chemotherapy. Indeed, Breslow is the co‐discoverer of a highly successful drug, Vorinostat, which is FDA‐approved for the treatment of cutaneous T‐cell lymphoma. We thank Professor Breslow for joining our project honoring his and our friend, Tetsuo Nozoe. Tetsuo Nozoe would have would have been deeply touched. —Jeffrey I. Seeman Guest Editor University of Richmond Richmond, Virginia 23173, USA E‐mail: jseeman@richmond.edu Ronald Breslow with Koji Nakanishi (left) and Tetsuo Nozoe (center), Sendai, 1970. Abstract We contributed to the field of non‐benzenoid aromatic compounds by creating the cyclopropenyl cation and various of its derivatives, including cyclopropenone; it was the first aromatic system with other than six pi electrons in a single ring, and the simplest aromatic system. The pioneering work of Tetsuo Nozoe in tropolone chemistry was celebrated with the founding of ISNA, the International Symposium on Non‐Benzenoid Aromatic Compounds, where I described our work in the field. It fit the prediction that aromaticity would be found in systems with 4n + 2 pi electrons, where n is an integer. I was also concerned with the properties of monocyclic systems with 4n cyclically conjugated pi electrons. They were expected not to be aromatic, but the interesting question was whether they were actually antiaromatic, especially destabilized by the cyclic conjugation in such 4n species as the cyclopropenyl anion, cyclobutadiene, and cyclopentadienyl cation. The evidence supports antiaromaticity in these cases. We also examined compounds where 4n cyclic pi systems were fused with aromatic systems, and most interestingly systems in which two 4n pi systems were fused. In these cases the periphery of the molecules had 4n + 2 pi electrons, for aromaticity, but the components were antiaromatic. Recently we have studied electrical conductivities in aromatic molecules such as thiophe...

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Section: Aromaticitymentioning

confidence: 99%

Section: Antiaromaticitymentioning

confidence: 99%

Novel Aromatic and Antiaromatic Systems

Breslow

2014

The Chemical Record

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“…In acetonitrile, the reduction potential of TrCl is approximately +0.51-0.53 V vs. SHE. 53,54 TrCl has been reacted in the past with lithium naphthalenide to generate the parent naphthalene and trityl radical dimer. 55 The focus of this paper is to distinguish if and which chemical discharging agents can provide a simple and effective way to avoid oxidations and adventitious functionalizations in restoring pristine nanocarbons.…”

Section: •−mentioning

confidence: 99%

Chemical routes to discharging graphenides

et al. 2017

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Chemical and electrochemical reduction methods allow the dispersion, processing, and/or functionalization of discrete sp-hybridised nanocarbons, including fullerenes, nanotubes and graphenes. Electron transfer to the nanocarbon raises the Fermi energy, creating nanocarbon anions and thereby activating an array of possible covalent reactions. The Fermi level may then be partially or fully lowered by intended functionalization reactions, but in general, techniques are required to remove excess charge without inadvertent covalent reactions that potentially degrade the nanocarbon properties of interest. Here, simple and effective chemical discharging routes are demonstrated for graphenide polyelectrolytes and are expected to apply to other systems, particularly nanotubides. The discharging process is inherently linked to the reduction potentials of such chemical discharging agents and the unusual fundamental chemistry of charged nanocarbons.

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“…Thus in spite of the greater number of resonance forms that can be written for the system with the double bond, the conjugation in the 3-membered ring of four  electrons was destabilizing [76][77][78]. Using electrochemistry on some of the stable cations in the cyclopropene series we were also able to get information about the energy of the corresponding radicals in which we had added one electron to the system [79] and later used electrochemistry to generate the highly reactive cyclopropenyl anion and measure its energy.…”

Section: Anti-aromaticitymentioning

confidence: 99%