Dynamics of the Degenerate Rearrangement of Bicyclo[3.1.0]hex-2-ene

Doubleday, Charles; Suhrada, Christopher P.; Houk, K. N.

doi:10.1021/ja050722w

Cited by 113 publications

(78 citation statements)

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“…In a recent illustration of this effect in a Diels-Alder reaction, Singleton and coworkers found that the product ratio predicted by trajectory calculations is strongly correlated with the direction of momenta at the TS (29). In our trajectory study of a diradical-mediated fourfold degen- erate rearrangement (30) reported experimentally by Baldwin and Keliher (31), we found that the product ratio is related in a simple way to the momentum distribution at the TS and that the distribution of structures is also important. A closely related issue is post-TS product selectivity, often on a bifurcating PES (32,33) or involving chemical activation of an intermediate from high energy reactants (34,35).…”

mentioning

confidence: 63%

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

Black

Liu

et al. 2012

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

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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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mentioning

confidence: 63%

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

Black

Liu

et al. 2012

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

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191

203

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“…Despite these caveats, the projection of the full dynamics into the reduced dimensional space is a powerful method to visualize both the reaction dynamics and the post-TS bifurcation in the reaction mechanism. 57,58 Direct Dynamics. Initial Conditions.…”

Section: ■ Simulation Methodsologymentioning

confidence: 99%

Reaction Path Bifurcation in an Electrocyclic Reaction: Ring-Opening of the Cyclopropyl Radical

et al. 2015

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Following previous work [J. Chem. Phys. 2013, 139, 154108] on a simple model of a reaction with a post-transition state valley ridge inflection point, we study the chemically important example of the electrocyclic cyclopropyl radical ring-opening reaction using direct dynamics and a reduced dimensional potential energy surface. The overall reaction requires con- or disrotation of the methylenes, but the initial stage of the ring-opening involves substantial internal rotation of only one methylene. The reaction path bifurcation is then associated with the relative sense of rotation of the second methylene. Clear deviations of reactive trajectories from the disrotatory intrinsic reaction coordinate (IRC) for the ring-opening are observed and the dynamical mechanism is discussed. Several features observed in the model system are found to be preserved in the more complex and higher dimensional ring-opening reaction. Most notable is the sensitivity of the reaction mechanism to the shape of the potential manifested as a Newtonian kinetic isotope effect upon deuterium substitution of one of the methylene hydrogens. Dependence of the product yield on frictional dissipation representing external environmental effects is also presented. The dynamics of the post-transition state cyclopropyl radical ring-opening are discussed in detail, and the use of low dimensional models as tools to analyze complicated organic reaction mechanisms is assessed in the context of this reaction.

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“…46 The rearrangement occurs through the formation of a diradical. 46 The rearrangement occurs through the formation of a diradical.…”

Section: Bicyclo[310]hex-2-ene 20mentioning

confidence: 99%

“…Doubleday et al 46 then performed classical trajectory simulations for the rearrangement of 20. The trajectories were performed using direct dynamics, where the energy surface was computed using the AM1-SRP method.…”

Section: Bicyclo[310]hex-2-ene 20mentioning

confidence: 99%

Organic Reaction Dynamics

Bachrach

2014

Computational Organic Chemistry

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In the previous chapters, we have focused our discussion of reaction mechanisms on the critical points along the reaction path. These critical points-local energy minima (reactants, intermediates, and products) and transition states (TSs)-were discussed in terms of their geometries and energies. We discussed the nature of the mechanism in terms of the topology of the potential energy surface (PES), the structure of the TSs, and the presence or absence of intermediates. We think of reactants progressing over TSs on to intermediates, perhaps through multiple intermediates and ending at products. This path is called the reaction coordinate and corresponds to the intrinsic reaction coordinate (IRC) or the minimum energy path (MEP) (see Section 1.6 for discussion on these two paths).This standard mechanistic analysis has a long successful history. Organic chemistry textbooks are filled with PESs and discussions of the implication of single-step versus multiple-step mechanisms, concerted TSs, and so on. 1,2 Transition state theory (TST) and Rice-Ramsperger-Kassel-Marcus (RRKM) theory provide tools for predicting rates based upon simple assumptions built upon the notion of reaction on the PES following the reaction coordinate. 3,4 An often-overlooked aspect of standard reaction mechanistic thought is that it really addresses only half of the picture. We talk about the positions of the atoms during the course of the reaction and the relative energies of points along the reaction path, but no mention is made of the time evolution of this process. In classical mechanics, description of a reactive system requires not just the particle positions but their momenta as well. The same is true for a quantum mechanical description, though one must keep in mind the limits imposed by the Heisenberg Uncertainty Principle. A complete description of a molecular reaction requires knowledge of both the position and the momentum of every atom for the entire time it takes for reactants to convert into products. This kind of description falls under the term molecular dynamics (MD).A few simple examples should suffice to demonstrate the critical role that MD plays in chemical reactions. Conservation of momentum must be enforced. Atoms and molecular fragments in motion must maintain their motion unless some barrier or force is applied to them. Consider the reaction of cis-2-butene with Computational Organic Chemistry, Second Edition. Steven M. Bachrach

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Dynamics of the Degenerate Rearrangement of Bicyclo[3.1.0]hex-2-ene

Cited by 113 publications

References 35 publications

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

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

Reaction Path Bifurcation in an Electrocyclic Reaction: Ring-Opening of the Cyclopropyl Radical

Organic Reaction Dynamics

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