Structure of Cyclo-octatetraene

Kaufman, H. S.; Fankuchen, I.; Mark, Howard

doi:10.1038/161165a0

Cited by 55 publications

(17 citation statements)

References 4 publications

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“…In contrast to planar Bz, the isolated COT molecule exists in a "tub-like" conformation [47] in order to reduce angle strain. However, when adsorbed on the surface considered here, the planar structure of the carbon atoms is approximately restored.…”

Section: Structuresmentioning

confidence: 99%

Atomic-scale inversion of spin polarization at an organic-antiferromagnetic interface

et al. 2013

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Using first-principles calculations, we show that the magnetic properties of a two-dimensional antiferromagnetic transition-metal surface are modified on the atomic scale by the adsorption of small organic molecules. We consider benzene (C6H6), cyclooctatetraene (C8H8) and a small transition metal -benzene complex (BzV) adsorbed on a single atomic layer of Mn deposited on the W(110) surface -a surface which exhibits a nearly antiferromagnetic alignment of the magnetic moments in adjacent Mn rows. Due to the spin-dependent hybridization of the molecular pz orbitals with the d states of the Mn monolayer there is a significant reduction of the magnetic moments in the Mn film. Furthermore, the spin-polarization at this organic-antiferromagnetic interface is found to be modulated on the atomic scale, both enhanced and inverted, as a result of the molecular adsorption. We show that this effect can be resolved by spin-polarized scanning tunneling microscopy (SP-STM). Our simulated SP-STM images display a spatially-dependent spin-resolved vacuum charge density above an adsorbed molecule -i.e., different regions above the molecule sustain different signs of spin polarization. While states with s and p symmetry dominate the vacuum charge density in the vicinity of the Fermi energy for the clean magnetic surface, we demonstrate that after a molecule is adsorbed those d-states, which are normally suppressed due to their symmetry, can play a crucial role in the vacuum due to their interaction with the molecular orbitals. We also model the effect of small deviations from perfect antiferromagnetic ordering, induced by the slight canting of magnetic moments due to the spin spiral ground state of Mn/W(110). PACS numbers:arXiv:1308.0934v2 [cond-mat.mtrl-sci]

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Section: Structuresmentioning

confidence: 99%

Atomic-scale inversion of spin polarization at an organic-antiferromagnetic interface

et al. 2013

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“…For instance, Zeonjuk et al (47) investigated six combinations of Lewis acids (boranes) and Lewis bases (phosphines) that showed different reactivity in H 2 activation. One of them, t Bu 3 P plus B(p-C 6 F 4 H) 3 , could catalyze reversible hydrogen activation, with a Gibbs energy barrier of 22.6 kcal/mol in solvent, and an exothermicity of 0.3 kcal/mol. In the context of B,N-based FLPs, Yepes et al (48) studied the hydrogen activation by the geminal aminoborane-based frustrated Lewis pairs (R 2 N-CH 2 -BR′ 2 ).…”

Section: Sidewaysmentioning

confidence: 99%

“…It features four cis-or Z double bonds in a characteristic nonplanar D 2d tub shape (3). From a combined femtosecond rotational coherence spectroscopy and theoretical study we have the molecule's precise gas-phase structure, with bond lengths r e (C-C) = 1.470, r e (C=C) = 1.337, and r e (C-H) = 1.079 Å (4).…”

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confidence: 99%

“…Our structure search in the Cambridge Structural Database (CSD) revealed a subunit in the structure of 9,9′,10,10′-tetradehydrodianthracene that resembles the (Z,E,Z,E)-COT structure (22). The CSD also contains one fascinating molecule, a di-Fe(CO) 3 complex of COT that approximates this geometry (23), but the organometallic bonding naturally changes the bonding picture. We also have not yet studied the possible products of intramolecular rearrangement [which play such an interesting role in the chemistry of the (Z,Z,Z,Z) form (14,16)] of the B isomer.…”

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confidence: 99%

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Stabilizing a different cyclooctatetraene stereoisomer

Lei

Xie

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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An unconventional cis-cis-cis-trans or (Z,Z,Z,E) structure B of cyclooctatetraene (COT) is calculated to lie only 23 kcal/mol above the well-known tub-shaped (Z,Z,Z,Z) isomer A; one example of this type of structure is known. The barrier for B returning to A is small, 3 kcal/mol. However, by suitable choice of substituents, the (Z,Z,Z,E) isomer can be made to lie in energy below the tub-shaped structure. Steric, clamping, and electronic strategies are proposed for achieving this. In the steric strategy, the C 8 H 4 (CH 3 ) 2 (C( t Bu) 3 ) 2 structure B is predicted to lie 21 kcal/mol below structure A, which is separated from form B only by a small barrier. A simple clamping strategy, effective for COT planarization, does not influence the A/B isomerization much. But, if the clamping group is aromatic (a fused benzene, pyrrole, thiophene, furan), the subtle interplay of potential aromaticity with clamping can be used to confer persistence if not stability on the (Z,Z,Z,E) isomer. An electronic strategy of a different kind, push-pull substitution on the COT ring, was not very effective in stabilizing the B form. However, it led us to vicinal amine-borane-substituted normal COTs that proved to be quite good at activating H 2 in a frustrated Lewis pair scenario. The molecule is most certainly not aromatic, in accord with Hückel's rule (2). It features four cis-or Z double bonds in a characteristic nonplanar D 2d tub shape (3). From a combined femtosecond rotational coherence spectroscopy and theoretical study we have the molecule's precise gas-phase structure, with bond lengths r e (C-C) = 1.470, r e (C=C) = 1.337, and r e (C-H) = 1.079 Å (4). Potential ring inversion and bond-bond switching in COT have fascinated the organic community for decades (5-7). The planar D 4h structure of COT is a transition state (TS) for the ring inversion (calculated barrier height of 10-14 kcal/mol) (8-12). The D 8h bondswitching TS lies a few kilocalories per mole higher. The accepted automerization surface is summarized schematically in Fig. 1.Motivated by the recent determination of the structures of some asymmetrically substituted COTs (13), we began a systematic study of COTs. Some peculiar geometries, far away from the tub shape, emerged; in time we identified them as cis-cis-cistrans (Z,Z,Z,E) isomers of COT. Stabilizing these structures is the aim of this article.(Z,Z,Z,E)-COT structures already appear in the theoretical and experimental literature. Conesa and Rzepa in 1998 predicted this isomer to lie 21-29 kcal/mol above the conventional all-Z structure, with a small barrier to return to all-Z COT (14). In their studies of Möbius aromaticity, Havenith et al. (15) optimized a C 8 H 8 (Z,Z,Z,E) structure, finding it again 21-29 kcal/mol above (Z,Z,Z,Z). And, in a comprehensive paper on the photochemistry and thermal rearrangements of COT, Garavelli et al. (16) found the (Z,Z,Z,E) isomer as a reaction intermediate, 24 to 25 kcal/mol above normal COT. The primary interest in their wideranging paper was in the photochemistry o...

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“…A similar conclusion was reached by Bastiansen & Hassel from an electron diffraction investigation (110). However, Kaufman, Fankuchen & Mark concluded from a crystal structure study that the molecule had a "tub" configuration with alternating carbon-carbon bond lengths (111). A prelimi nary report of a recent electron diffraction study by I. Karle supports the "tub" structure with alternating C-C links (112).…”

Section: Structuresmentioning

confidence: 92%

Experimental Molecular Structure

Roth¹

1951

Annu. Rev. Phys. Chem.

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The principal sources of information about the structure of molecules in the free state are electron diffraction of gases, spectroscopy in the infrared, Raman and microwave regions, and x-ray diffraction of crystals. The past year has seen a continuation of the trends noted in the previous review by Beach (1). The general structural principles for most small molecules are reasonably well understood, and interest now is directed toward the under standing of variations of bond distances and angles in different molecules and the study of more complicated systems, such as larger molecules and the nature of intramolecular motions.The advances in experimental technique in electron and x-ray diffraction and the striking interpretations of pure rotational spectra in the microwave region are beginning to provide a body of information relating to interatomic parameters where the distances are reliable to 0.01 'A or better and the angles reliable to 30'. Some success is obtained in accounting for the observed inter atomic distances by modifying the sum of the covalent radii (14) with cor rections for ionic or multiple bond character (18), but it is apparent that there is a need for precise data from a largernumberof molecules. Accordingly, much of the work at the present time is concerned with improving experi mental techniques or with redetermining the structures of many molecules by the newer methods.Electron diffraction.-The need for the determination of a larger number of parameters has led many workers in the field of electron diffraction to search for increased sensitivity and objectivity. The early electron diffraction investigations were accomplished by the visual correlation technique, where calculated intensity patterns based on assumed models were compared with the visually observed diffraction pattern. As the complexity of the molecules studied increased and it became necessary to determine a larger number of parameters, it became increasingly difficult to arrive at a unique model. At the present time, many molecules are being reinvestigated and extensive work is being done to increase the accuracy and sensitivity of the experimen tal techniques.Recent papers by . the Karles (2, 3, 4) and Hastings & Bauer (5, 8) con tain detailed discussions of the effects of various experimental factors on the diffraction patterns: the proper design of a gas nozzle for introducing the sample into the electron beam, the effect of finite sampJe size and divergence of the beam, mUltiple scattering, the use of beam stops and rotating sectors, and the response characteristics of photographic emulsions.1 This review is a continuation of that of Beach (1) and covers approximately the year 19 50.

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Structure of Cyclo-octatetraene

Cited by 55 publications

References 4 publications

Atomic-scale inversion of spin polarization at an organic-antiferromagnetic interface

Atomic-scale inversion of spin polarization at an organic-antiferromagnetic interface

Stabilizing a different cyclooctatetraene stereoisomer

Experimental Molecular Structure

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