Nonstatistical Dynamics in Unlikely Places: [1,5] Hydrogen Migration in Chemically Activated Cyclopentadiene

Goldman, Lawrence Michael; Glowacki, David R.; Carpenter, Barry K.

doi:10.1021/ja1095717

Cited by 44 publications

(47 citation statements)

References 57 publications

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“…Even when the branching of reaction paths does occur at a local PES minimum, classical molecular dynamics (MD) simulations have shown that one cannot rely on the validity of the statistical approximation for gas-phase reactions. 15,16,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] The Figure 1. Schematic depiction of a PES with a bifurcating reaction path.…”

Section: Changes In the Code Of Behaviormentioning

confidence: 99%

The Study of Reactive Intermediates in Condensed Phases

2016

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Novel experimental techniques and computational methods have provided new insight into the behavior of reactive intermediates in solution. The results of these studies show that some of the earlier ideas about how reactive intermediates ought to behave in solution were incomplete or even incorrect. This perspective summarizes what the new experimental and computational methods are, and draws attention to the shortcomings that their application has brought to light in previous models. Key areas needing further research are highlighted.

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Section: Changes In the Code Of Behaviormentioning

confidence: 99%

The Study of Reactive Intermediates in Condensed Phases

2016

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“…[11][12][13][14][15][16][17][18][19] Alongside these observations, a growing number of studies have shown that the extent of vibrational excitation and its subsequent relaxation dynamics can actually impact reaction outcomes in solvents. [20][21][22] For example, there is good evidence that thermal reactions as well-known as alkene hydroboration have a Markovnikov/AntiMarkovnikov product ratio which is determined by the extent of nascent vibrational excitation in the short lived addition complex. 12,23 Recently, it has even been suggested that solute/solvent interactions which take place in the course of transient vibrational relaxation dynamics provide a route to enantioselective amplification.…”

Section: Introductionmentioning

confidence: 99%

Non-equilibrium reaction and relaxation dynamics in a strongly interacting explicit solvent: F + CD3CN treated with a parallel multi-state EVB model

Glowacki

Orr-Ewing

Harvey

2015

The Journal of Chemical Physics

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We describe a parallelized linear-scaling computational framework developed to implement arbitrarily large multi-state empirical valence bond (MS-EVB) calculations within CHARMM and TINKER. Forces are obtained using the Hellmann-Feynman relationship, giving continuous gradients, and good energy conservation. Utilizing multi-dimensional Gaussian coupling elements fit to explicitly correlated coupled cluster theory, we built a 64-state MS-EVB model designed to study the F + CD3CN → DF + CD2CN reaction in CD3CN solvent (recently reported in Dunning et al. [Science 347(6221), 530 (2015)]). This approach allows us to build a reactive potential energy surface whose balanced accuracy and efficiency considerably surpass what we could achieve otherwise. We ran molecular dynamics simulations to examine a range of observables which follow in the wake of the reactive event: energy deposition in the nascent reaction products, vibrational relaxation rates of excited DF in CD3CN solvent, equilibrium power spectra of DF in CD3CN, and time dependent spectral shifts associated with relaxation of the nascent DF. Many of our results are in good agreement with time-resolved experimental observations, providing evidence for the accuracy of our MS-EVB framework in treating both the solute and solute/solvent interactions. The simulations provide additional insight into the dynamics at sub-picosecond time scales that are difficult to resolve experimentally. In particular, the simulations show that (immediately following deuterium abstraction) the nascent DF finds itself in a non-equilibrium regime in two different respects: (1) it is highly vibrationally excited, with ∼23 kcal mol−1 localized in the stretch and (2) its post-reaction solvation environment, in which it is not yet hydrogen-bonded to CD3CN solvent molecules, is intermediate between the non-interacting gas-phase limit and the solution-phase equilibrium limit. Vibrational relaxation of the nascent DF results in a spectral blue shift, while relaxation of the post-reaction solvation environment results in a red shift. These two competing effects mean that the post-reaction relaxation profile is distinct from what is observed when Franck-Condon vibrational excitation of DF occurs within a microsolvation environment initially at equilibrium. Our conclusions, along with the theoretical and parallel software framework presented in this paper, should be more broadly applicable to a range of complex reactive systems.

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“…There has been some contention over the best way to model the energy loss, but on the whole such models have been highly successful for gas-phase calculations, and have started to see use in condensed phases. 6,7,8,9 Importantly, the selectivity expected for propene in the absence of collisional cooling would be lower than experiment while the selectivity expected if INT (R = Me) cooled fully is higher than experiment. As a result, any model for the energy loss would necessarily be able to reproduce experiment with a fitted cooling parameter.…”

Section: Introductionmentioning

confidence: 83%

Failure and Redemption of Statistical and Nonstatistical Rate Theories in the Hydroboration of Alkenes

Bailey

Singleton

2017

J. Am. Chem. Soc.

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Our previous work found that canonical forms of transition state theory incorrectly predict the regioselectivity of the hydroboration of propene with BH3 in solution. In response, it has been suggested that alternative statistical and nonstatistical rate theories can adequately account for the selectivity. This paper uses a combination of experimental and theoretical studies to critically evaluate the ability of these rate theories, as well as dynamic trajectories and newly developed localized statistical models, to predict quantitative selectivities and qualitative trends in hydroborations on a broader scale. The hydroboration of a series of terminally substituted alkenes with BH3 was examined experimentally, and a classically unexpected trend is that the selectivity increases as the alkyl chain is lengthened far from the reactive centers. Conventional and variational transition state theories can neither predict the selectivities nor the trends. The canonical competitive nonstatistical model makes somewhat better predictions for some alkenes but fails to predict trends, and it performs poorly with an alkene chosen to test a specific prediction of the model. Added nonstatistical corrections to this model make the predictions worse. Parameterized RRKM-master equation calculations correctly predict the direction of the trend in the selectivity versus alkene size but overpredict its magnitude, and the selectivity with large alkenes remains unpredictable with any parameterization. Trajectory studies in explicit solvent can predict selectivities without parameterization but are impractical for predicting small changes in selectivity. From a lifetime and energy analysis of the trajectories, “localized RRKM-ME” and “competitive localized noncanonical” rate models are suggested as steps toward a general model. These provide the best predictions of the experimental observations and insight into the selectivities.

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Nonstatistical Dynamics in Unlikely Places: [1,5] Hydrogen Migration in Chemically Activated Cyclopentadiene

Cited by 44 publications

References 57 publications

The Study of Reactive Intermediates in Condensed Phases

The Study of Reactive Intermediates in Condensed Phases

Non-equilibrium reaction and relaxation dynamics in a strongly interacting explicit solvent: F + CD3CN treated with a parallel multi-state EVB model

Failure and Redemption of Statistical and Nonstatistical Rate Theories in the Hydroboration of Alkenes

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