Antiaromaticity in Open-Shell Cyclopropenyl to Cycloheptatrienyl Cations, Anions, Free Radicals, and Radical Ions

Allen, Annette D.; Tidwell, Thomas T.

doi:10.1021/cr990316t

Cited by 152 publications

(117 citation statements)

References 146 publications

(130 reference statements)

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“…Accordingly, cyclic conjugation of 4nπ-electrons is considered to be energetically unfavorable. In fact, some 4nπ-electron systems such as cyclobutadiene [8,9] and cyclopropenyl anion [10,11] led to strong destabilization of the compound in contrast to the stabilization characteristic of aromatic compounds. Breslow proposed the term of antiaromaticity to describe such systems [12,13].…”

Section: Open Accessmentioning

confidence: 99%

Recent Studies on the Aromaticity and Antiaromaticity of Planar Cyclooctatetraene

2010

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Cyclooctatetraene (COT), the first 4nπ-electron system to be studied, adopts an inherently nonplanar tub-shaped geometry of D 2d symmetry with alternating single and double bonds, and hence behaves as a nonaromatic polyene rather than an antiaromatic compound. Recently, however, considerable 8π-antiaromatic paratropicity has been shown to be generated in planar COT rings even with the bond alternated D 4h structure. In this review, we highlight recent theoretical and experimental studies on the antiaromaticity of hypothetical and actual planar COT. In addition, theoretically predicted triplet aromaticity and stacked aromaticity of planar COT are also briefly described.

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Section: Open Accessmentioning

confidence: 99%

Recent Studies on the Aromaticity and Antiaromaticity of Planar Cyclooctatetraene

2010

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“…It has been argued that such odd-electron systems are, at least in some cases, destabilized by antiaromaticity. [18] However, NICS calculations of the [2+2] cycloreversion of the cyclobutane radical cation show a non-aromatic character of the transition structure. [19] In addition, many concerted transition states of radical cations are also symmetric and subject to first-and secondorder Jahn-Teller distortions as discussed above, which makes a symmetry-preserving pathway even more unfavorable.…”

Section: Aromaticity Of Transition Statesmentioning

confidence: 99%

Structure and Reactivity of Radical Ions: New Twists on Old Concepts

Donoghue¹,

Wiest²

2006

Chemistry A European J

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Electron transfer is the simplest reaction possible, yet it has a profound impact on the structure and reactivity of organic compounds. These changes allow a new look at some of the fundamental concepts that are used to explain organic chemistry, such as symmetry, aromaticity, and bonding. The results from high-level electronic structure calculations are used to analyze the mechanistic differences in the pericyclic reactions of simple hydrocarbons and their radical cation counterparts. The importance of state symmetry correlation, Jahn-Teller distortions, delocalization, and fractional bonding for the reaction pathways of hydrocarbon radical cations is discussed.

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“…Interestingly, the NICS profiles of this series ( Figure 5) show that, while neutral 1 and monoanionic compound [1] − behave the same way, the dianion [1] 2− exhibits a shallow minimum at ca. 1 Å above/below the central ring.…”

Section: Monoborolesmentioning

confidence: 92%

“…[1,2] To this class of compounds belong the five-membered boroles, compounds that are isoelectronic to the cyclopentadienyl cation C5H5 + and comprise four π electrons. The unfavorable π-conjugation in these systems exerts a destabilizing effect and thus contributes to their high reactivity, which is the reason why stable borole derivatives can only be achieved by annulation [3] or employing bulky substituents around the reactive BC4 core.…”

Section: Introductionmentioning

confidence: 99%

A theoretical study of the aromaticity in neutral and anionic borole compounds

et al. 2015

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Abstract:In this contribution, we have evaluated the (anti)aromatic character of thirty-four different borole compounds in their neutral and reduced states based on two aromaticity indices, namely nucleus-independent chemical shift (NICS) and multicenter indices (MCI), calculated at the PBE0/6-31+G(d,p) level of theory. Both indices corroborate the notion that neutral borole compounds are antiaromatic and become increasingly aromatic upon addition of electrons. Effects of the ring substituents on the degree of (anti)aromaticity are discussed together with differences in the two theoretical methods, which are on the one hand based on magnetic (NICS) and on the other hand based on electronic criteria (MCI).

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Antiaromaticity in Open-Shell Cyclopropenyl to Cycloheptatrienyl Cations, Anions, Free Radicals, and Radical Ions

Cited by 152 publications

References 146 publications

Recent Studies on the Aromaticity and Antiaromaticity of Planar Cyclooctatetraene

Recent Studies on the Aromaticity and Antiaromaticity of Planar Cyclooctatetraene

Structure and Reactivity of Radical Ions: New Twists on Old Concepts

A theoretical study of the aromaticity in neutral and anionic borole compounds

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