syn, Anti isomerization of 5,5?-Bis-5H-dibenzo[a,d]cyclohepten-5-ylidene

Agranat, Israel; Suissa, M. Rachel

doi:10.1007/bf00672100

Cited by 18 publications

(18 citation statements)

References 36 publications

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“…[73] Adding the PM3-calculated relative energy of s Ϫ 0.5 kcal/mol Ϫ one arrives at 36.9 kcal/ mol, which compares very well with the PM3-calculated energy of the [a-s] transition state: 37.6 kcal/mol. However, the complete conversion of s to a observed in the experiment [76] is not consistent with the calculated relative energy of 0.5 kcal/mol.…”

Section: Dynamic Stereochemistry Of Bi-5h-dibenzo[ad]-cyclohepten-5-supporting

confidence: 51%

“…Energies of the twisted and syn-folded conformations and of the transition states for enantiomerization, conformational inversion, and E,Z isomerization, relative to the global minimum (anti-folded) conformations of 2, 3, 9, and 11 [kcal/mol] Twisted conformation [a] syn-Folded conformation Enantiomerization or E,Z Isomerization barrier [ [73] ant transition states are summarized in Table 9. For comparison, experimental values are given in parenthesis.…”

Section: Discussionmentioning

confidence: 99%

“…[103] The syn ǟ Ǟ anti isomerization barrier of bi-5H-dibenzo[a,d]cyclohepten-5-ylidene (11) was found to be even higher Ϫ ∆G ‡ 347 ϭ 36.4 kcal/mol Ϫ in a bistricyclic ene with central seven-membered rings. [73] A PM3 study of the a ǟ Ǟ t conformational isomerization of bianthrone (4) has previously been reported. [110,111] PM3 results on bifluorenylidene (2), dixanthylene (3), diselenoxanthylene (1, X,Y: Se), ditelluroxanthylene (1, X,Y: Te), the methylene-bridged ene 10, and the isopropylidenebridged 1 (1, X,Y: C(CH 3 ) 2 ) have been reported.…”

Section: Dynamic Stereochemistrymentioning

confidence: 99%

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Conformational Space and Dynamic Stereochemistry of Overcrowded Homomerous Bistricyclic Aromatic Enes − A Theoretical Study

2001

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The conformational spaces and dynamic stereochemistry of representative overcrowded homomerous bistricyclic aromatic enes (1, X = Y) are investigated, applying the semiempirical PM3 method. The experimental energy barriers for E,Z isomerizations, enantiomerizations, and conformational inversions of 1 and related compounds, derived from DNMR and other kinetic studies, are reviewed. This study focuses on the analysis of the minima, transition states, and dynamic mechanisms of the conformational isomerizations of bifluorenylidene (2), dixanthylene (3), dithioxanthylene (9), and bi-5H-dibenzo[a,d]cyclohepten-5-ylidene (11). The four representative bistricyclic enes differ in the sizes of their central rings and in their bridging groups. The mechanisms of the interconversions

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Section: Dynamic Stereochemistry Of Bi-5h-dibenzo[ad]-cyclohepten-5-supporting

confidence: 51%

Section: Discussionmentioning

confidence: 99%

Section: Dynamic Stereochemistrymentioning

confidence: 99%

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Conformational Space and Dynamic Stereochemistry of Overcrowded Homomerous Bistricyclic Aromatic Enes − A Theoretical Study

2001

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“…Recently, the concept of biradicaloid has been extended to non-planar aromatic systems such as overcrowded ethylenes (OCEs). [24][25][26][27][28] While planar biradicaloids undergo rapid thermal equilibrium between singlet and triplet states in the absence of an attending conformational change, non-planar biradicaloids embedded with anthraquinodimethane (AQD) groups undergo large conformational changes between folded closed-shell singlet and twisted open-shell triplet forms. Wu, [29,30] Campos, [31] Suzuki, [32,33] Campaña, [34] Sun, [35] and we [36] have described various AQD-based non-planar biradicaloids which incorporate diarylmethyl, fluorenyl, dihydrodimethylanthryl (DMA), dibenzosuberenyl (DBS) and nanohoop units (Figure 1b).…”

Section: Introductionmentioning

confidence: 99%

Synthesis of π-Extended Thiele's and Chichibabin's Hydrocarbons and Effect of the π-congestion on Conformations and Electronic States

Nishiuchi

Aibara

Sato

et al. 2022

Preprint

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The biradicaloid of Chichibabin’s hydrocarbon exits in a unique thermal equilibrium between closed-shell singlet and open-shell triplet forms. Conceptually, the incorporation of non-planar aromatic groups, such as anthraquinodimethane (AQD), in these species could bring about stabilization of the individual singlet and triplet spin biradicaloids by creating a high energy barrier for con-formational interconversion between folded (singlet) and twisted (triplet) forms. Moreover, this alteration could introduce the possibility of controlling spin states through conformational changes induced by chemical and physical processes. Herein, we report the preparation of AQD containing, π-extended Thiele's (A-TH) and Chichibabin's (A-CH) hydrocarbons, which have highly π-congested structures resulting from the presence of bulky 9-anthryl units. The π-congestion in these substances leads to steric frustration about carbon-carbon double bonds, and creates flexible dynamic motion with a moderate activation barrier between folded singlet and twisted triplet states. These constraints make it possible to isolate the twisted triplet state of A-CH. In addition, simple mechanical grinding of the folded singlet of A-CH produces the twisted triplet.

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“…The parent TBHF exhibits photo-and thermal isomerization between their anti-and syn-folded isomers because flipping of a seven-membered ring is hampered by steric hindrance in the overcrowded fjord region around the central C=C double bond (Scheme 1). [37][38][39][40] . This observation can also be found in other types of TBHFs, as reported by Miao and co-workers.…”

Section: ■ Introductionmentioning

confidence: 99%

Photo- and Thermal Interconversion of Multiconfigurational Strained Hydrocarbons Exhibiting Completely Switchable Oxidation to Stable Dicationic Dyes

2019

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Highly strained hydrocarbons with two di-/tri-benzocycloheptatriene units were designed as electrochromic overcrowded ethylenes that undergo reversible interconversion with stable dicationic dyes. Due to severe steric repulsion, two configurational isomers (anti,anti-folded and syn,anti-folded forms) were isolated as stable entities. Photo-and thermal interconversion of these isomers proceeded cleanly: one-way photoisomerization occurred from anti,anti-to syn,anti-form and one-way thermal isomerization was observed from syn,anti-to anti,anti-form. Even though both isomers undergo twoelectron oxidation into the same twisted dications, quite different oxidation potentials enable completely selective oxidation of syn,anti-isomers. Thus, the present multi-configurational strained hydrocarbons are capable of switching of activation/deactivation of their electrochromic properties by light/heat.

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syn, Anti isomerization of 5,5?-Bis-5H-dibenzo[a,d]cyclohepten-5-ylidene

Cited by 18 publications

References 36 publications

Conformational Space and Dynamic Stereochemistry of Overcrowded Homomerous Bistricyclic Aromatic Enes − A Theoretical Study

Conformational Space and Dynamic Stereochemistry of Overcrowded Homomerous Bistricyclic Aromatic Enes − A Theoretical Study

Synthesis of π-Extended Thiele's and Chichibabin's Hydrocarbons and Effect of the π-congestion on Conformations and Electronic States

Photo- and Thermal Interconversion of Multiconfigurational Strained Hydrocarbons Exhibiting Completely Switchable Oxidation to Stable Dicationic Dyes

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