Ground states of molecules. 58. The C4H4 potential surface

Kollmar, Herbert; Carrión, Francisco J.; Dewar, Michael J. S.; Bingham, Richard C.

doi:10.1021/ja00408a004

Cited by 89 publications

(53 citation statements)

References 5 publications

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“…Indeed, the GD and DC vectors at CI tetra show that the diagonal carbon or hydrogen atoms partly intersect. Our preliminary calculation indicates that CI tetra is connected to the diradical S 0 intermediate [22,23] of S 0 tetrahedrane. This criss-cross reaction process is expected to be similar to that of cyclooctatetraene [25].…”

Section: Tetra-radical S 1 /S 0 Conical Intersectionmentioning

confidence: 84%

“…However, the shape of a PES around the intermediate structure sometimes becomes a conical intersection (CI) between a ground state and an excited state [19][20][21]. Although the S 0 PES of C 4 H 4 has been explored in detail [22,23], the possible existence of CIs has not been considered. Consequently, we were motivated to locate the structure where the PES of Ia intersects with that of Ib.…”

Section: Introductionmentioning

confidence: 99%

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Tetra-radical and ionic S1/S0 conical intersections of cyclobutadiene

Sumita

Saito

2010

Chemical Physics

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Section: Tetra-radical S 1 /S 0 Conical Intersectionmentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Tetra-radical and ionic S1/S0 conical intersections of cyclobutadiene

Sumita

Saito

2010

Chemical Physics

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“…Of course there are many other C4H4 isomers [601 which could be involved. However, none of these is as stable as VA 1601, and under shock tube conditions they would be collisionally stabilized only after isomerization to VA. Both the H, elimination processes, (2) and (41, and the H-atom scissions of reactions (3) the path analogous to C2H4 dissociation suggested by KWKY [51, and…”

Section: Kinetic Mechanismmentioning

confidence: 99%

The mechanism of the homogeneous pyrolysis of acetylene

Kiefer

Drasek

1990

Int J of Chemical Kinetics

118

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The experimental literature on the pyrolysis of C,H2 is reviewed and summarized. These observations divide naturally into three temperature regimes: (i) T < 1100 K, where the homogeneous reaction is a molecular polymerization; (ii) 1100 < T < 1800 K, where the process is still dominated by a molecular polymerization, but a fragment radical chain is clearly involved; and (iii) T > 1800 K, where a fragment chain carried by C2H and H drives a polymerization to polyacetylenes. A combined molecular/fragment chain mechanism is developed and applied to the modeling of three shock-tube studies which span the two higher-temperature regimes. The core of the mechanism is a set of 5 mainly molecular reactions whose rates are derived from an application of unimolecular rate theory and detailed balance to recent measurements on the decomposition of vinylacetylene. The combination of this core with consequent fragment radical reactions provides a satisfactory description of most features of the chosen experiments including several-isotope exchange, hydrogenation to CzH4, and CsH, formation-which are almost entirely the result of fragment radical chain reaction. Possible detailed paths for the molecular dimerization are suggested and some possible molecular paths for the "Berthelot synthesis" of benzene are also proposed.The last 30 years has seen a tremendous increase in our understanding of the pyrolysis and combustion reactions of hydrocarbon fuels. Detailed, very complete, and quite successful mechanisms have now been devised for simple fuels [l-31. Despite all this progress there remain many unresolved questions of mechanism, some of the most serious being those which involve the reactions of acetylene, which is of course a major product, or at least an important intermediate, in all high temperature hydrocarbon pyrolysis and combustion.The C,H2 pyrolysis mechanism has been particularly unyielding. Here both molecular (possibly diradical) and fragment-radical (monoradical) chain mechanisms have been proposed, but neither seems consistent with all the data, and it remains unclear how either process might be initiated.This article presents an attempt to arrive at a fully consistent model of the pyrolysis mechanism, albeit one which only treats the early stages of the process. The basis for this model lies in the recent resurrection of the molecular reaction concept by Duran, Amorbieta, and Colussi (DAC) [41, and Kiefer, Mitchell, Kern, and Yong (KMKY) [51. The core of the paper is a detailed, quantitative modeling of some recent shock-tube data [6-91, using a mechanism which contains both molecular and fragment-radical chain reactions. This is followed by a consideration of the full range of

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“…Thus, the rearrangement of tetrahedrane to cyclobutadiene or two acetylenes is strongly unfavorable, as reactions to 6-8 are, since the corresponding reaction barriers are sizable, in marked contrast to previous lower-level predictions. [15,24] Although 1 is highly strained, [13,19,20,23,29,32] it is not reactive, and should, in principle, be isolable. This is even more intriguing in light of the fact that strain, measured as a net effect is generally underestimated because of the neglect of thermodynamically stabilizing factors.…”

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confidence: 99%

Tetrahedrane—Dossier of an Unknown

Nemirowski

Reisenauer

Schreiner

2006

Chemistry A European J

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To probe whether tetrahedrane should be isolable the thermodynamics and kinetics of C4H4 singlet and triplet structures were studied extensively at the CCSD(T)/cc-pVTZ//CCSD(T)/cc-pVDZ, CCSD(T)/cc-pVDZ, CCSD(T)/cc-pVDZ//B3 LYP/6-311G**, and B3 LYP/6-311G** levels of theory. The reaction of cyclopropene with atomic carbon, which was previously suggested to involve tetrahedrane as a reactive intermediate, was re-examined experimentally with low-temperature matrix-isolation techniques. While experimental and theoretical results exclude the intermediacy of tetrahedrane in the above reaction, it is predicted to be an isolable molecule. Among the many C4H4 species, we pay special attention to the electronic effects on the ground state multiplicity of the respective carbenes.

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Ground states of molecules. 58. The C4H4 potential surface

Cited by 89 publications

References 5 publications

Tetra-radical and ionic S1/S0 conical intersections of cyclobutadiene

Tetra-radical and ionic S1/S0 conical intersections of cyclobutadiene

The mechanism of the homogeneous pyrolysis of acetylene

Tetrahedrane—Dossier of an Unknown

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