Limits on the activation parameters for automerization of cyclobutadiene-1,2-d2

Whitman, David W.; Carpenter, Barry K.

doi:10.1021/ja00387a065

Cited by 133 publications

(108 citation statements)

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“…[40] To summarize, the present theoretical results provide strong computational evidence that isomers 1 and 3 are bond-stretch isomers, thus enriching a set of these very rare species encompassing 1,2-and 1,8-dichloroperfluoro-cyclooctatetraene pair, [7] as well as cyclobutadiene as a special case. [6] It is, therefore, hoped that our results will stimulate additional synthetic efforts to prepare both isomers in pure or substituted forms. A judicious choice of substituents should be helpful in this respect, as discussed in the preceding paper.…”

Section: Discussionmentioning

confidence: 87%

“…[5] The situation is more promising in organic chemistry. In addition to the paradigmatic cyclobutadiene automerization interconversion, [6] there is a well-established pair of bond-stretch isomers: 1,2-and 1,8-dichloroperfluorocyclooctatetraenes. [7] However, these systems are more exceptions than a rule, and the bottom line is that the experimental detection of bond-stretch isomerism turned out to be extremely difficult and elusive.…”

Section: Introductionmentioning

confidence: 99%

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On the Bond‐Stretch Isomerism in the Benzo[1,2:4,5]dicyclobutadiene System—An ab initio MR‐AQCC Study

Antol¹,

Eckert‐Maksić²,

Lischka³

et al. 2004

ChemPhysChem

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Bond-stretch isomerism in benzo[1,2:4,5]dicyclobutadienle (BDCB) has been investigated using the MR-AQCC/6-31G(d) method, a high-level multireference ab initio approach including size-extensivity corrections. The applied theoretical approach includes both nondynamical and dynamical electron correlation effects. Full MR-AQCC geometry optimizations of localized (1) and delocalized (3) isomers as well as the transition structure (TS) have been determined using D2h, symmetry restriction. The calculations show that both isomers are approximately of equal stability separated by a barrier with a height of about 5 kcal mol(-1). Thus, the present results strongly indicate that benzof[1,3:4,5]dicyclobutadiene is a very good candidate for an organic compound exhibiting bond-stretch isomerism, since isomers 1 and 3 correspond to true minima on the double-well potential energy surface, which are separated by a sufficiently high barrier. It is particularly important to emphasize that isomer 3 represents a realization of the highly elusive quasi-[10]annulene.

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Section: Discussionmentioning

confidence: 87%

Section: Introductionmentioning

confidence: 99%

On the Bond‐Stretch Isomerism in the Benzo[1,2:4,5]dicyclobutadiene System—An ab initio MR‐AQCC Study

Antol¹,

Eckert‐Maksić²,

Lischka³

et al. 2004

ChemPhysChem

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“…The barrier height has been measured to be in the range 1.6-10 kcal/mol [96,97]. The stabilization energy ∆E(1 1 B 1g − 1 1 A g ) going from square to rectangular geometry has been calcultated [85][86][87][88][89][90][91]93,94,98] between 5 and 13 kcal/mol according to the results of Table 4.…”

Section: Structural Instabilitiesmentioning

confidence: 99%

Structures of Annulenes and Model Annulene Systems in the Ground and Lowest Excited States

Gellini

Salvi

2010

Symmetry

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The paper introduces general considerations on structural properties of aromatic, antiaromatic and non-aromatic conjugated systems in terms of potential energy along bond length alternation and distortion coordinates, taking as examples benzene, cyclobutadiene and cyclooctatetraene. Pentalene, formally derived from cyclooctatetraene by cross linking, is also considered as a typical antiaromatic system. The main interest is concerned with [n]annulenes and model [n]annulene molecular systems, n ranging from 10 to 18. The rich variety of conformational and configurational isomers and of dynamical processes among them is described. Specific attention is devoted to bridged [10]-and [14]annulenes in the ground and lowest excited states as well as to s-indacene and biphenylene. Experimental data obtained from vibrational and electronic spectroscopies are discussed and compared with ab initio calculation results. Finally, porphyrin, tetraoxaporphyrin dication and diprotonated porphyrin are presented as annulene structures adopting planar/non-planar geometries depending on the steric hindrance in the inner macrocycle ring. Radiative and non-radiative relaxation processes from excited state levels have been observed by means of time-resolved fluorescence and femtosecond transient absorption spectroscopy. A short account is also given of porphycene, the structural isomer of porphyrin, and of porphycene properties.

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“…It dimerizes in solid matrices at ! 35 K, is a transient reactive intermediate in solution, and has a lifetime of only 2 ms at 0.1 Torr in the gas phase.[1a] Nevertheless, trapping [4] and spectroscopic results have revealed that cyclobutadiene has a ground-state singlet configuration and adopts a rectangular D 2h structure which rapidly undergoes automerization. An isolable and room temperature stable complex consisting of 1 in the cavity of a spherical crown ether (that is, a hemicarceplex) has even been prepared, [5] but the thermodynamic stability of cyclobutadiene remains experimentally unknown.…”

mentioning

confidence: 99%

The Heat of Formation of Cyclobutadiene

et al. 2006

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Cyclobutadiene (1) and its derivatives have beckoned to chemists ever since Kekules deduction of the structure of benzene and his attempt to synthesize 1 in 1872.[1] Pioneering efforts by Willstätter and Finkelstein were followed by a century of studies which produced many remarkable findings. Room temperature stable derivatives such as tri-tert-butylcyclobutadiene [2] and tetra-tert-butylcyclobutadiene [3] were successfully prepared and spectroscopically characterized, whereas the parent compound was found to be more elusive. It dimerizes in solid matrices at ! 35 K, is a transient reactive intermediate in solution, and has a lifetime of only 2 ms at 0.1 Torr in the gas phase.[1a] Nevertheless, trapping [4] and spectroscopic results have revealed that cyclobutadiene has a ground-state singlet configuration and adopts a rectangular D 2h structure which rapidly undergoes automerization. An isolable and room temperature stable complex consisting of 1 in the cavity of a spherical crown ether (that is, a hemicarceplex) has even been prepared, [5] but the thermodynamic stability of cyclobutadiene remains experimentally unknown.Conventional calorimetric methods are precluded when it comes to cyclobutadiene and its simple derivatives because of their high reactivity. Electrochemical, [6] pK a , [7] and kinetic [8] measurements of model compounds have been carried out and interpreted as indicating that 1 has a negative resonance energy of at least 50-67 kJ mol À1 . This conclusion is in accord with many of the early computational findings and a

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Limits on the activation parameters for automerization of cyclobutadiene-1,2-d2

Abstract: In this communication we report temperature and concentration dependence studies on the trapping of vicinally dideuterated cyclobutadiene in dichloromethane solution. The results allow limits

Cited by 133 publications

References 0 publications

On the Bond‐Stretch Isomerism in the Benzo[1,2:4,5]dicyclobutadiene System—An ab initio MR‐AQCC Study

On the Bond‐Stretch Isomerism in the Benzo[1,2:4,5]dicyclobutadiene System—An ab initio MR‐AQCC Study

Structures of Annulenes and Model Annulene Systems in the Ground and Lowest Excited States

The Heat of Formation of Cyclobutadiene

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