Structural dependence of the rotational barrier in calicenes

Gleicher, Gerald Jay; Arnold, James C.

doi:10.1016/0040-4020(73)80002-x

Cited by 9 publications

(4 citation statements)

References 21 publications

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“…23 The first calculations on the rotational barrier were performed in 1972 24 and predicted a value of 27 kcal mol -1 . A subsequent semiempirical prediction of more than 55 kcal mol -1 was recognized as unlikely to be accurate, 25 although a later calculation at the Hartree-Fock (HF) level predicted a barrier of 44 kcal mol -1 . 11 Substituent effects were estimated to have influences of 10-30% on the computed rotational barriers.…”

Section: Introductionmentioning

confidence: 99%

Quantum Chemical Characterization of Low-Energy States of Calicene in the Gas Phase and in Solution

et al. 2007

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The ground and excited electronic state properties of calicene (triapentafulvalene or 5-(cycloprop-2-en-1-ylidene)cyclopenta-1,3-diene) have been studied with a variety of density functional models (mPWPW91, PBE, TPSS, TPSh, B3LYP) and post-Hartree-Fock models based on single (MP2 and CCSD(T)) and multideterminantal (CASPT2) reference wave functions. All methods agree well on the properties of ground-state calicene, which is described as a conjugated double bond system with substantial zwitterionic character deriving from a charge-separated mesomer in which the three-and five-membered rings are both aromatic. Although the two rings are joined by a formal double bond, contributions from the aromatic mesomer reduce its bond order substantially. A rotational barrier of 40-41 kcal mol -1 is predicted in the gas phase and solvation effects reduce the barrier to 37 and 33 kcal mol -1 in benzene and water, respectively, because of increased zwitterionic character in the twisted transition-state structure. Multistate CASPT2 (MS-CASPT2) is used to characterize the first few excited singlet and triplet states and indicates that the most important transition occurs at 4.93 eV (251 nm). A cis-trans photoisomerization about the inter-ring double bond is found to be inefficient.

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Section: Introductionmentioning

confidence: 99%

Quantum Chemical Characterization of Low-Energy States of Calicene in the Gas Phase and in Solution

et al. 2007

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“…Since, in polarized structures such as 2 , the interring CC double bond is formally a single bond, rotation about this bond can be anticipated, although it is likely to be restricted and thus potentially slow on the NMR time scale. However, experimental dynamic NMR studies have not yet been reported, although theoretical calculations at various levels of theory have been published. − In this respect, 1 is the best studied molecule, where the barriers to rotation calculated at the MP2 level in the gas phase (40−41 kcal mol -1 ), in benzene (37 kcal mol -1 ), and in water (33 kcal mol -1 ) have been reported . For sesquifulvalene 6 , a similar value at the same level of theory has been obtained (41.5 kcal mol -1 ) 12a.…”

Section: Introductionmentioning

confidence: 71%

“…However, experimental dynamic NMR studies have not yet been reported, although theoretical calculations at various levels of theory have been published. [9][10][11] In this respect, 1 is the best studied molecule, where the barriers to rotation calculated at the MP2 level in the gas phase (40-41 kcal mol -1 ), in benzene (37 kcal mol -1 ), and in water (33 kcal mol -1 ) have been reported. 11 For sesquifulvalene 6, a similar value at the same level of theory has been obtained (41.5 kcal mol -1 ).…”

Section: Introductionmentioning

confidence: 99%

Quantification of the (Anti)Aromaticity of Fulvalenes Subjected to π-Electron Cross-Delocalization

2007

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Fulvalenes 3-12 were theoretically studied at the ab initio level of theory. For the global minima structures, the occupation of the bonding (pi)C=C orbital of the interring C=C double bond obtained by NBO analysis quantitatively proves pi-electron cross-delocalization resulting in, at least partially, 2- or 6pi-electron aromaticity and 8pi-electron antiaromaticity for appropriate moieties. The cross-conjugation was quantified by the corresponding occupation numbers and lengths of the interring C=C double bonds, while the aromaticity or antiaromaticity due to cross-delocalization of the pi-electrons was visualized and quantified by through-space NMR shielding surfaces.

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“…[172] The structural dependence of the rotational barrier in calicenes received theoretical consideration as early as 1973. [173] Comparisons of singlet biradical and zwitterionic states in the planar and 90°twisted forms allows for predictions on the relative stabilities of the two states from the degree of polarisation in the planar structure. [125] The excitation of calicene is associated with considerable molecular charge transfer [174] and the electro-optical absorption spectrum of tetrachlorodiphenyl 74 (see Scheme 14) has been examined.…”

Section: Triapentafulvalenes (Calicenes)mentioning

confidence: 99%

The Fulvalenes

Halton

2005

Eur J Org Chem

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The fulvalenes are the class of hydrocarbons obtained by formally cross‐conjugating two rings through a common exocyclic double bond. Although the first report of such a compound dates to 1915, study of the series began in earnest only in the 1950s, and even today many of the unsubstituted parent hydrocarbons remain unknown. The following report, the first to specifically address this class of molecules, summarises the information available from research published to the end of 2004 and offers some suggestions for future study. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

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Structural dependence of the rotational barrier in calicenes

Cited by 9 publications

References 21 publications

Quantum Chemical Characterization of Low-Energy States of Calicene in the Gas Phase and in Solution

Quantum Chemical Characterization of Low-Energy States of Calicene in the Gas Phase and in Solution

Quantification of the (Anti)Aromaticity of Fulvalenes Subjected to π-Electron Cross-Delocalization

The Fulvalenes

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