Gas-Phase Ionic Reactions: Dynamics and Mechanism of Nucleophilic Displacements

Chabinyc, Michael L.; Craig, Stephen L.; Regan, Colleen K.; Brauman, John I.

doi:10.1126/science.279.5358.1882

Cited by 292 publications

(233 citation statements)

References 52 publications

(27 reference statements)

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“…[18][19][20][21][22] Having been so extensively studied, by both experimental [23][24][25][26][27] and computational [28][29][30][31][32][33][34][35][36] means, lends this class of reactions to be an outstanding starting position for benchmarking and refining new computational methods and techniques. In particular, the chloride/methyl chloride reaction is a strong candidate as a prototype reaction as it has been quite extensively studied in order to understand the exact nature of the transition state in the gas and condensed phases.…”

Section: Introductionmentioning

confidence: 99%

Quantum mechanical study of solvent effects in a prototype SN2 reaction in solution: Cl− attack on CH3Cl

Kuechler

York

2014

The Journal of Chemical Physics

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The nucleophilic attack of a chloride ion on methyl chloride is an important prototype S N 2 reaction in organic chemistry that is known to be sensitive to the effects of the surrounding solvent. Herein, we develop a highly accurate Specific Reaction Parameter (SRP) model based on the Austin Model 1 Hamiltonian for chlorine to study the effects of solvation into an aqueous environment on the reaction mechanism. To accomplish this task, we apply high-level quantum mechanical calculations to study the reaction in the gas phase and combined quantum mechanical/molecular mechanical simulations with TIP3P and TIP4P-ew water models and the resulting free energy profiles are compared with those determined from simulations using other fast semi-empirical quantum models. Both gas phase and solution results with the SRP model agree very well with experiment and provide insight into the specific role of solvent on the reaction coordinate. Overall, the newly parameterized SRP Hamiltonian is able to reproduce both the gas phase and solution phase barriers, suggesting it is an accurate and robust model for simulations in the aqueous phase at greatly reduced computational cost relative to comparably accurate ab initio and density functional models. © 2014 AIP Publishing LLC. [http://dx

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Section: Introductionmentioning

confidence: 99%

Quantum mechanical study of solvent effects in a prototype SN2 reaction in solution: Cl− attack on CH3Cl

Kuechler

York

2014

The Journal of Chemical Physics

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“…1,2 The Walden inversion reaction mechanism of the X − + CH 3 Ytype S N 2 reactions is a textbook example of stereo-specific reaction pathways, in which the nucleophile (X − ) attacks the backside of the CH 3 Y molecule and replaces the leaving group (Y − ) while the configuration is being inverted around the carbon center. However, recent theoretical and experimental investigations showed that the dynamics is not so simple.…”

Section: Introductionmentioning

confidence: 99%

Accurate ab initio potential energy surface, thermochemistry, and dynamics of the F− + CH3F SN2 and proton-abstraction reactions

Szabó

Telekes

Czakó

2015

The Journal of Chemical Physics

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Articles you may be interested inWe develop a full-dimensional global analytical potential energy surface (PES) for the F − + CH 3 F reaction by fitting about 50 000 energy points obtained by an explicitly correlated composite method based on the second-order Møller-Plesset perturbation-F12 and coupled-cluster singles, doubles, and perturbative triples-F12a methods and the cc-pVnZ-F12 [n = D, T] basis sets. The PES accurately describes the (a) back-side attack Walden inversion mechanism involving the pre-and post-reaction (b) ion-dipole and (c) hydrogen-bonded complexes, the configuration-retaining (d) front-side attack and (e) double-inversion substitution pathways, as well as (f) the proton-abstraction channel. The benchmark quality relative energies of all the important stationary points are computed using the focal-point analysis (FPA) approach considering electron correlation up to coupled-cluster singles, doubles, triples, and perturbative quadruples method, extrapolation to the complete basis set limit, core-valence correlation, and scalar relativistic effects. The FPA classical(adiabatic) barrier heights of (a), (d), and (e) are −0.45(−0.61), 46.07(45.16), and 29.18(26.07) kcal mol −1 , respectively, the dissociation energies of (b) and (c) are 13.81(13.56) and 13.73(13.52) kcal mol −1 , respectively, and the endothermicity of (f) is 42.54(38.11) kcal mol −1 . Quasiclassical trajectory computations of cross sections, scattering (θ) and initial attack (α) angle distributions, as well as translational and internal energy distributions are performed for the F − + CH 3 F(v = 0) reaction using the new PES. Apart from low collision energies (E coll ), the S N 2 excitation function is nearly constant, the abstraction cross sections rapidly increase with E coll from a threshold of ∼40 kcal mol −1 , and retention trajectories via double inversion are found above E coll = ∼30 kcal mol −1 , and at E coll = ∼50 kcal mol −1 , the front-side attack cross sections start to increase very rapidly. At low E coll , the indirect mechanism dominates (mainly isotropic backward-forward symmetric θ distribution and translationally cold products) and significant long-range orientation effects (isotropic α distribution) and barrier recrossings are found. At higher E coll , the S N 2 reaction mainly proceeds with direct rebound mechanism (backward scattering and hot product translation). C 2015 AIP Publishing LLC. [http://dx

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“…Both experiments and simulations have shown that the chemical dynamics of gas-phase X − + CH 3 Y → XCH 3 + Y − S N 2 nucleophilic substitution reactions are nonstatistical [36][37][38]. Reactions, such as Cl − + CH 3 Br → ClCH 3 + Br − , have X − -CH 3 Y and XCH 3 -Y − ion-dipole complexes separated by a central barrier and the unimolecular dynamics of these complexes are intrinsically non-RRKM.…”

Section: P(t) = I F I K I Ementioning

confidence: 99%

Models for Intrinsic Non-RRKM Dynamics. Decomposition of the SN2 Intermediate Cl––CH3Br

Paranjothy

Sun

Paul

et al. 2013

Zeitschrift Für Physikalische Chemie

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Chemical dynamics simulations, based on both an analytic potential energy surface (PES) and direct dynamics, were used to investigate the intrinsic non-RRKM dynamics of the Cl products were fit with multi-exponential functions. The intrinsic non-RRKM dynamics is more pronounced for the simulations with the analytic PES than by direct dynamics, with the populations for the former and latter primarily represented by tri-and bi-exponential functions, respectively. For the analytic PES and direct dynamics simulations, the intrinsic non-RRKM dynamics is more important for the isomerization pathway to form ClCH 3 -Br − than for dissociation to Cl − + CH 3 Br. Since the decomposition probability of Cl − -CH 3 Br is non-exponential, the Cl − -CH 3 Br unimolecular rate constant depends on pressure, with both high and low pressure limits. The high pressure limit is the RRKM rate constant and for the simulations with the analytic PES the rate constant decreased by a factor of 3.0, 5.6, and 4.3 in going from the high to low pressure limit for total energies of 40, 60, and 80 kcal/mol. For the direct dynamics simulations these respective factors are 2.4, 1.4, and 1.2. A separable phase space model with intermolecular and intramolecular complexes describes some of the simulation results, but overall models advanced for intrinsic non-RRKM dynamics give incomplete representations of the intermediate and product populations vs. time determined from the simulations.

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Gas-Phase Ionic Reactions: Dynamics and Mechanism of Nucleophilic Displacements

Cited by 292 publications

References 52 publications

Quantum mechanical study of solvent effects in a prototype SN2 reaction in solution: Cl− attack on CH3Cl

Quantum mechanical study of solvent effects in a prototype SN2 reaction in solution: Cl− attack on CH3Cl

Accurate ab initio potential energy surface, thermochemistry, and dynamics of the F− + CH3F SN2 and proton-abstraction reactions

Models for Intrinsic Non-RRKM Dynamics. Decomposition of the SN2 Intermediate Cl––CH3Br

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