Concerted and nonconcerted pathways for thermal conversions of deuterium-labeled cyclohexenes to butadienes and ethylenes

Lewis, David; Brandt, Benjamin; Crockford, L.; Glenar, D. A.; Rauscher, Grant; Rodriguez, J. A.; Baldwin, John E.

doi:10.1021/ja00078a011

Cited by 23 publications

(27 citation statements)

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“…As it was discussed in the previous section, considering the results obtained by Lewis [13,14] and the good agreement with the kinetic and thermodynamic parameters from Tsang's experiment, the more probable reaction pathway is mechanism A. TS2c opening has no inductive or resonance stabilization and resembles with Mechanism B in the case of cyclohexene. C4-C12 distance has no important variations in both compounds since C12 is not adjacent to the carbon bearing the unpaired electron.…”

Section: Transition State and Reaction Mechanismssupporting

confidence: 58%

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Inquiry of the reaction paths in thermal retro-Diels–Alder reactions in the gas phase: Theoretical study on the concerted and stepwise elimination mechanisms of cyclohexenes

Ramirez

Córdova

Ruette

et al. 2015

Computational and Theoretical Chemistry

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Section: Transition State and Reaction Mechanismssupporting

confidence: 58%

“…The retro-Diels-Alder reaction of deuterated cis-4,5-d 2 -cyclohexene was also examined above 820 o C by Lewis et al [13,14]. The percentage of product distribution of the cis/trans deuterated ethylene increased with temperature from 5% to 33%.…”

Section: Introductionmentioning

confidence: 99%

Inquiry of the reaction paths in thermal retro-Diels–Alder reactions in the gas phase: Theoretical study on the concerted and stepwise elimination mechanisms of cyclohexenes

Ramirez

Córdova

Ruette

et al. 2015

Computational and Theoretical Chemistry

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“…Trajectories were run for reactions R1-8 at 298 K and reactions R1-3 at higher temperatures: 1,180 K for R1, 849 K for R2, and 1,017 K for R3, which correspond to Lewis and Baldwin's experimental temperatures (12,13). High temperature trajectories were initialized at variational transition states for concerted cycloaddition located by Polyrate (36).…”

Section: Methodsmentioning

confidence: 99%

“…Similarly, 1.0% of trajectories in the reaction of cyclohexadiene and ethylene (R3) lead to diradicals at 1,017 K, while no trajectories in the reaction of cyclopentadiene and ethylene (R2) at 849 K involve diradical intermediates. Lewis and Baldwin determined that the retro-DA reaction of cis-4,5-d 2 -cyclohexene (R1) at 1,180 K yields 9% transd 2 -ethylene (12), and the maximum amount of trans-d 2 -ethylene that could have gone undetected was 1.3% for R2 and 6.3% for R3 (13). We have not included an estimate of diradicals formed from the higher energy stepwise TS.…”

mentioning

confidence: 99%

Dynamics, transition states, and timing of bond formation in Diels–Alder reactions

Black

Liu

et al. 2012

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

190

203

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The time-resolved mechanisms for eight Diels-Alder reactions have been studied by quasiclassical trajectories at 298 K, with energies and derivatives computed by UB3LYP/6-31G(d). Three of these reactions were also simulated at high temperature to compare with experimental results. The reaction trajectories require 50-150 fs on average to transverse the region near the saddle point where bonding changes occur. Even with symmetrical reactants, the trajectories invariably involve unequal bond formation in the transition state. Nevertheless, the time gap between formation of the two new bonds is shorter than a C─C vibrational period. At 298 K, most Diels-Alder reactions are concerted and stereospecific, but at high temperatures (approximately 1,000 K) a small fraction of trajectories lead to diradicals. The simulations illustrate and affirm the bottleneck property of the transition state and the close connection between dynamics and the conventional analysis based on saddle point structure.molecular dynamics | density functional theory | transition state theory | cycloadditions | concerted reaction T he Diels-Alder reaction is one of the most important reactions used in organic synthesis (1, 2), and its discovery was recognized by the Nobel Prize in Chemistry in 1950. The reaction is a paradigm for methods that efficiently increase structural complexity, because two single bonds, a six-membered ring, and up to four stereocenters are formed in a single step.Mechanisms of Diels-Alder reactions have been the subject of intensive scrutiny by experimental and theoretical methods (3-6). The timing of bond formation has been the focus of attention. Many experimental studies show that the Diels-Alder reaction is stereospecific with respect to both reactants (7), a result that is compatible with a concerted mechanism, traditionally defined as a reaction path involving no intermediates. DFT and ab initio calculations based on transition state theory predict that a concerted, one-step mechanism is the lowest energy pathway on the ground-state potential energy surface (PES) (8). However, at the time-resolved level, the two new carbon-carbon bonds may not form simultaneously along a dynamical trajectory. The time gap between formation of the two bonds is strongly connected to the expected degree of stereospecificity observed in the reaction, but the details of this relationship are uncertain due to several recent reports: (i) In studies of retro-Diels-Alder (retro-DA) dynamics at femtosecond time resolution of reaction R2 in Scheme 1, Zewail and coworkers found two sets of transients, one identified with concerted asynchronous trajectories, the other with diradicaloid stepwise trajectories (9, 10). Because reactants are photochemically activated, a full understanding of the experiments must include the role of conical intersections between ground and excited states (11). (ii) In thermal shock tube studies of the retro-DA reactions R1, R2, and R3 in Scheme 1, Lewis, Baldwin, and coworkers found that the retro-DA reaction of cis-4...

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“…Interesting enough, the polymer chains ended with reactive alkyne and azide functional groups could be reclicked under ultrasonication. Thus, addition of CuI and irradiation with stirring at 80 C for 19 h resulted in a polymeric material having a molecular weight similar to that of the presonicated material. In short, ultrasound convincingly converts a usually irreversible reaction into a useful reversible process with further expectations.…”

mentioning

confidence: 95%

Harnessing mechanochemical effects with ultrasound-induced reactions

Cravotto

Cintas

2012

Chem. Sci.

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Chemical reactions may experience numerous and varied effects under the influence of ultrasound. This soft radiation, often viewed as a lab trick, induces and improves both physical and chemical transformations by means of efficient agitation, dissolution, mass and heat transfers, and reagents sonolysis, which all arise from the cavitational collapse. An empirical rationale that distinguishes between true chemical effects and mechanical ones, especially in heterogeneous reactions, was introduced more than two decades ago and has been a useful guidance on reporting sonochemical mechanisms. Recent studies have witnessed a truly remarkable data set that boosts sonochemistry over the wall of applied science. This perspective highlights the importance of the so-called false sonochemistry-closely related to mechanochemistry-in modern synthesis, thus illustrating the advantages of using pressure waves in chemistry. Emphasis is put on green transformations, mild polymerization reactions and the selective cleavage of functionalized polymers, which may have an effective impact in process chemistry and represent a realistic option in industry.

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Concerted and nonconcerted pathways for thermal conversions of deuterium-labeled cyclohexenes to butadienes and ethylenes

Cited by 23 publications

References 0 publications

Inquiry of the reaction paths in thermal retro-Diels–Alder reactions in the gas phase: Theoretical study on the concerted and stepwise elimination mechanisms of cyclohexenes

Inquiry of the reaction paths in thermal retro-Diels–Alder reactions in the gas phase: Theoretical study on the concerted and stepwise elimination mechanisms of cyclohexenes

Dynamics, transition states, and timing of bond formation in Diels–Alder reactions

Harnessing mechanochemical effects with ultrasound-induced reactions

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