Gas-phase elimination kinetics of ethyl esters of chloroacetate, 3-chloropropionate, and 4-chlorobutyrate. The electronic effects of substituents at the acyl carbon

Chuchani, Gabriel; Triana, Juana Ledia; Rotinov, Alexandra; CARABALLO, D. F.

doi:10.1021/j150609a030

Cited by 13 publications

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“… a Ref . b Ref . c Ref . d Ref . e Ref . f Ref . g Ref . h Ref . i Ref . j Ref . k Ref . l Ref . m Ref . n Ref . o Note that the selection of internal coordinate systems does not affect UM-T since it only samples torsional modes. …”

Section: Resultsmentioning

confidence: 99%

Comparative Analysis of Uncoupled Mode Approximations for Molecular Thermochemistry and Kinetics

Lin

2022

J. Chem. Theory Comput.

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The accurate prediction of thermochemistry and kinetic parameters is an important task for reaction modeling. Unfortunately, the commonly used harmonic oscillator model is often not accurate enough due to the absence of anharmonic effects. In this work, we improve the representation of an anharmonic potential energy surface (PES) using uncoupled mode (UM) approximations, which model the full-dimensional PES as a sum of one-dimensional potentials of each mode. We systematically analyze different PES sampling schemes and coordinate systems for constructing the one-dimensional potentials, and benchmark the performance of UM methods on data sets of molecular thermochemistry and kinetic properties. The results show that the accuracy of the UM approach strongly depends on how the one-dimensional potentials are defined. If one-dimensional potentials are constructed by sampling along normal mode directions (UM-N) or along the directions that minimize intermode coupling (E- and E′-optimized), the accuracies of the predicted properties are not significantly improved compared to the harmonic oscillator model. However, significant improvements can be achieved by sampling the torsional modes separately from the vibrational modes (UM-T and UM-VT). In this work, three types of coordinate systems are examined, including redundant internal coordinates (RIC), hybrid internal coordinates (HIC), and translation-rotation-internal coordinates (TRIC). The HIC and TRIC coordinate systems can outperform RIC since transition state species may contain large-amplitude interfragmentary motions that regular internal coordinates can not describe adequately. Among all the methods we examined, the activation energies and pre-exponential factors calculated using UM-VT with either TRIC or HIC best agree with the reference values. Since UM-VT requires only a number of additional single point energy calculations for each independent mode, the scaling of computational costs of UM-VT is the same as that of the standard harmonic oscillator model, making UM-VT an appealing way of calculating the thermochemistry and kinetic properties for large-size systems.

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Section: Resultsmentioning

confidence: 99%

Comparative Analysis of Uncoupled Mode Approximations for Molecular Thermochemistry and Kinetics

Lin

2022

J. Chem. Theory Comput.

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“…All the pathways proposed have contributed immensely to the outcome of the reaction. The most favourable pathway to this thermal decomposition through the experimental research has focused on pathways that give acetic acid and olefin [Chuchani et al, 1981;Rosas et al, 2010]. The first mechanism employed in the thermal decomposition of 1-phenyl ethyl acetate is based on the elimination pathway (Taylor 1983;Blades 1954;Hurd and Blunck, 1938).…”

Section: Introductionmentioning

confidence: 99%

Computational Investigation Into the Kinetics, Mechanism and Thermodynamics Properties of the Gas-Phase Thermal Decomposition of 1-Phenyl Ethyl Acetate

Esan¹,

Ogunyemi²,

Oyeneyin³

et al. 2023

FJS

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Kinetics and thermodynamics of gas-phase thermal decomposition of 1-phenylethyl acetate to vinyl benzene and acetic acid (ethanoic) were carried out using the density functional theory (DFT) method at B3LYP/6-31++G**. Geometric parameters obtained include atomic charge distribution, dihedral angles, bond lengths, and bond angle for the ground state reactant (GS), transition state (TS), and the product (PRD) while the thermodynamic parameters such as a change in entropy change (∆S), change in enthalpy (∆Hreaction) and free Gibbs energy were calculated at 623K with an interval of 25K. Kinetic parameters determined include activation energy (Ea), Pre-exponential Arrhenius factor (log A) and rate (k). Geometric results revealed that the decomposition reaction is through asynchronous cleavage of α-ether oxygen bonds and β-carbon-hydrogen in the six-membered cyclic transition state: C2-H1 and C5-O7 bond breaking occurred first while the C9-H1 bond formation process is lagging behind in a single step. The ∆S (5.867 J/mol/K); ∆Hreaction (38.45 kcal/mol), ∆G (39.69 kJ/mol), Ea (43.7 kcal/mol), log A (12.70) and k (6.1 x 10 -2 S -1 ) compared well with the experimental available results in literature at 623K. The intrinsic reaction coordinate (IRC) on the TS structures shows that the reactant connects to the respective minima while the Wilberg bond index shows that the TS possesses 'an early' character closer to the reactant than the products. The theoretical calculation method can be used to study the thermodynamics, mechanism and kinetics of the thermal decomposition of acetates thus reducing the cost, laboratory experiments time and exposure to hazardous chemicals.

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Homogeneous, unimolecular, gas-phase elimination of leaving groups at the alkoyl side of carboxylic acids

Chuchani

Rotinov

Domínguez

et al. 1996

J. Phys. Org. Chem.

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The molecular gas-phase elimination kinetics of the series CI (CH,).COOH (n = 1-4), show changes in mechanisms from polar five-centered intramolecular displacement of the CI leaving group by the acidic hydrogen of the COOH to neighboring group participation of the oxygen carbonyl of the COOH group. The mechanisms for the series 2-, 3-and 4-chlorobutyric acids are explained similarly as above. The leaving chloride at the 2-position of acetic, propionic, and butyric acids is displaced by the hydrogen of the COOH group through a prevaling path of a five-centered cyclic transition-state mechanism. This type of mechanism is also described for the pyrolysis of 2-hydroxy-, 2-alkoxy-, 2-phenoxy-, and 2-acetoxycarboxylic acids. The ease with which the groups at the 2-position of acetic and propionic acids are displaced by the H of COOH give rise theThese two sequences differ only in the OH leaving group position. Additional work on glycolic acid pyrolysis is needed to explain the above differences.

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Gas-phase elimination kinetics of ethyl esters of chloroacetate, 3-chloropropionate, and 4-chlorobutyrate. The electronic effects of substituents at the acyl carbon

Cited by 13 publications

References 0 publications

Comparative Analysis of Uncoupled Mode Approximations for Molecular Thermochemistry and Kinetics

Comparative Analysis of Uncoupled Mode Approximations for Molecular Thermochemistry and Kinetics

Computational Investigation Into the Kinetics, Mechanism and Thermodynamics Properties of the Gas-Phase Thermal Decomposition of 1-Phenyl Ethyl Acetate

Homogeneous, unimolecular, gas-phase elimination of leaving groups at the alkoyl side of carboxylic acids

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