Theoretical investigation of the oxidation pathways of HO•-initiated reactions of acrolein, methacrolein, and trans-crotonaldehyde

2009 ◽  
Vol 87 (12) ◽  
pp. 1716-1726 ◽  
Author(s):  
Sabry El-Taher
Keyword(s):  
Double Bond ◽  
Transition State ◽  
Correlation Energy ◽  
Single Point ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Methyl Substitution ◽  
Reactive Complex ◽  
Moller Plesset ◽  
Transition State Structures

Ab initio molecular-orbital calculations have been performed to investigate the reaction mechanisms of the HO•-initiated reactions of the α,β-unsaturated aldehydes: acrolein (ACR), methacrolein (MACR), and trans-crotonaldehyde (CROT). All geometries were fully optimized at the MP2(Full)/6–31G(d,p) level. The correlation energy corrections were introduced by carrying out single-point calculations using both spin-projected second-order Møller–Plesset perturbation theory (PMP2) and coupled-cluster theory (CCSD(T)) using basis sets of different sizes. All reaction pathways studied proceed via a barrierless formation of a loosely bound pre-reactive complex in the entrance channel. The transition-state structures of the HO• additions to the terminal (β) and to the central (α) carbon atoms of the C=C double bond are found to be reactant-like structures. The lowest-energy barrier pathways are found to be the aldehydic H-atom abstraction. The β-addition pathways are found to be energetically more favored than the α-addition pathways. The HO• addition and aldehydic H-atom abstraction pathways are found to be highly exoergic, with the H-atom abstraction pathway being more exoergic than the addition pathways. Although the methyl substitution at the C=C double bond of methacrolein and crotonaldehyde lowers the energies of the transition-state structures of both α- and β-addition pathways, it destabilizes the energies of the transition-state structures of the corresponding aldehydic H-atom abstraction pathways, compared with that of acrolein.

Abinitio study on radical anions of nitro compounds

1992 ◽  
Vol 70 (2) ◽  
pp. 314-326 ◽  
Author(s):  
Fabio Ramondo
Keyword(s):  
Correlation Energy ◽  
Nitro Compounds ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Radical Anions ◽  
Electron Correlation Energy ◽  
Structural Differences ◽  
Moller Plesset ◽  
Planar Electron ◽  
Abinitio Calculations

The results of abinitio molecular orbital calculations on some nitro compounds, RNO2 (R = CH3, CF3, CH2F, BH2, BF2, BHF, C6H5) and on the corresponding radical anions are reported. The geometries of the neutral and charged species were optimized at the SCF and MP2 levels of theory employing the 6-31G* and the 6-31 + G* basis sets. The rotation about the CN and BN bonds reveals distinct conformations for each molecule and vibrational frequencies were determined for such structures. All the employed levels of theory predict structural differences between neutral and charged molecules. The major geometrical changes occurring by electron adding to RNO2 consist in the lengthening of the NO bonds and in the shortening of the CN and BN bonds. The radical anions are calculated to be pyramidal at nitrogen in the stable conformers of CH3NO2−, CF3NO2−, CH2FNO2−, while, for the π-electron-accepting substituents (BH2, BHF, BF2, C6H5), the anion is planar. Electron correlation energy corrections in the framework of Møller–Plesset perturbation theory were included to determine relative stabilities between different conformations. At the MP4/6-31G*//MP2/6-31G* level, an easy rotation of the NO2 group is predicted for all the radical anions and neutral molecules with the exception of BH2NO2−, BF2NO2−, and BHFNO2−, which show high torsional barriers about the BN bond. Keywords: nitro compounds, radical anions, abinitio calculations, molecular structure.

scholarly journals Popular Integration Grids Can Result in Large Errors in DFT-Computed Free Energies

2019 ◽  
Author(s):  
Andrea N. Bootsma ◽  
Steven Wheeler
Keyword(s):  
Transition State ◽  
Molecular Orientation ◽  
Density Functional ◽  
Basis Sets ◽  
Free Energies ◽  
Functional Theory ◽  
Metal Free ◽  
Stereoselective Reactions ◽  
Functionalization Reaction ◽  
Transition State Structures

<div>Density functional theory (DFT) has emerged as a powerful tool for analyzing organic and organometallic systems and proved remarkably accurate in computing the small free energy differences that underpin many chemical phenomena (e.g. regio- and stereoselective reactions). We show that the lack of rotational invariance of popular DFT integration grids reveals large uncertainties in computed free energies for isomerizations, torsional barriers, and regio- and stereoselective reactions. The result is that predictions based on DFT-computed free energies for many systems can change qualitatively depending on molecular orientation. For example, for a metal-free propargylation of benzaldehyde, predicted enantioselectivities based on B97-D/def2-TZVP free energies using the popular (75,302) integration grid can vary from 62:38 to 99:1 by simply rotating the transition state structures. Relative free energies for the regiocontrolling transition state structures for an Ir-catalyzed C–H functionalization reaction computed using M06/6-31G(d,p)/LANL2DZ and the same grid can vary by more than 5 kcal mol–1, resulting in predicted regioselectivities that range anywhere from 14:86 to >99:1. Errors of these magnitudes occur for different functionals and basis sets, are widespread among modern applications of DFT, and can be reduced by using much denser integration grids than commonly employed.</div>

Theoretical study on the insertion reaction of CH(X2Π) with CH4

1997 ◽  
Vol 75 (7) ◽  
pp. 996-1001 ◽  
Author(s):  
Zhi-Xiang Wang ◽  
Ming-Bao Huang. ◽  
Ruo-Zhuang Liu
Keyword(s):  
Electron Correlation ◽  
Energy Surface ◽  
Theoretical Study ◽  
Reaction Path ◽  
Basis Sets ◽  
Insertion Reaction ◽  
Molecular Orbital Calculations ◽  
Insertion Reactions ◽  
Moller Plesset ◽  
Ch Radical

The CH + CH4 reaction has been studied by means of ab initio molecular orbital calculations incorporating electron correlation with Møller–Plesset perturbation theory up to second and fourth orders with the 6-31G(d,p) and 6-311++G(2d,p) basis sets. An energetically feasible insertion reaction path has been found in the potential energy surface that confirms the experimental proposal for the mechanism of the CH + CH4 reaction. The feature of the mechanism for the CH + CH4 insertion reaction is found to be different from the feature of the mechanisms for the CH + NH3, CH + H2O, and CH + HF insertion reactions, but somewhat similar to that for the CH2 + CH4 insertion reaction. Energetic results for the CH + CH4 reactions are in agreement with experiment. Keywords: CH radical, methane, reaction mechanism.

Ab initio molecular orbital study of simple 1,3-dipolar reactions

1976 ◽  
Vol 29 (3) ◽  
pp. 465 ◽  
Author(s):  
D Poppinger
Keyword(s):  
Transition State ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Transition States ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Molecular Orbital Study ◽  
Orbital Study ◽  
Extended Basis ◽  
Optimized Geometries

Ab initio molecular orbital calculations with minimal and extended basis sets have been carried out for the 1,3-dipolar addition of fulminic acid to acetylene, ethylene, ethynamine and propynenitrile. Optimized geometries are reported for the transition states HCNO+C2H2, HCNO+C2H4, HCNO+ C2HNH2, for the adducts isoxazole and 2-isoxazoline, and for nitrosocyclopropene as a possible intermediate. The calculations indicate that (a) these 1,3-dipolar reactions are synchronous processes, (b) the geometry of the transition state is insensitive to substitution and (c) of the isomeric substituted adducts, 5-aminoisoxazole and isoxazole-4-carbonitrile should be formed preferentially.

scholarly journals Popular Integration Grids Can Result in Large Errors in DFT-Computed Free Energies

2019 ◽  
Author(s):  
Andrea N. Bootsma ◽  
Steven Wheeler
Keyword(s):  
Transition State ◽  
Molecular Orientation ◽  
Density Functional ◽  
Low Frequency ◽  
Basis Sets ◽  
Vibrational Modes ◽  
Free Energies ◽  
Functional Theory ◽  
Stereoselective Reactions ◽  
Transition State Structures

Density functional theory (DFT) has emerged as a powerful tool for analyzing (bio-)organic and organometallic systems and proved remarkably accurate in computing the small free energy differences that underpin many chemical phenomena (e.g. regio- and stereoselective reactions). We show that the lack of rotational invariance of popular DFT integration grids reveals large uncertainties in computed free energies for some isomerizations, torsional barriers, and regio- and stereoselective reactions. The result is that predictions based on DFT-computed free energies for systems with very low-frequency vibrational modes can change qualitatively depending on molecular orientation. For example, for a metal-free propargylation of benzaldehyde, predicted enantioselectivities based on B97-D/def2-TZVP free energies using a popular pruned (75,302) integration grid can vary from 62:38 to 99:1 by simply rotating the transition state structures. Relative free energies for the regiocontrolling transition state structures for an Ir-catalyzed C–H functionalization reaction computed using M06/6-31G(d,p)/LANL2DZ and the same grid can vary by more than 5 kcal/mol, resulting in predicted regioselectivities that range anywhere from 14:86 to >99:1. Errors of these magnitudes occur for different functionals and basis sets, are potentially widespread among modern applications of DFT, and can be reduced by using much denser integration grids than commonly employed.<br>

AB INITIO CALCULATIONS OF INTERMOLECULAR INTERACTION POTENTIALS OF FULLERENE-FRAGMENTS SYSTEMS

2005 ◽  
Vol 04 (01) ◽  
pp. 49-58 ◽  
Author(s):  
YUKIUMI KITA ◽  
KEI WAKO ◽  
ISAMU OKADA ◽  
MASANORI TACHIKAWA
Keyword(s):  
Ab Initio ◽  
Intermolecular Interaction ◽  
Correlation Energy ◽  
Basis Set ◽  
Basis Sets ◽  
Cubic Phase ◽  
Molecular Orbital Calculations ◽  
Interaction Potentials ◽  
Basis Set Superposition Error ◽  
Intermolecular Distances

We have performed the ab initio molecular orbital calculations for combinations of the fullerene-fragments as the models of the nonbonding interaction of C 60 dimer at the preferred configurations in the simple cubic phase. The intermolecular interaction potentials have been calculated using several basis sets with MP2 level of the electron correlation energy and the basis set superposition error correction. The strong dispersion attractions that is dominant in the van der Waals interaction has been found for the combinations of the fullerene-fragments. The equilibrium intermolecular distances obtained are in good agreement with the corresponding experimental value. The repulsive region of the intermolecular interaction calculated by ab initio method is found to be express by an atom–atom interaction potential with an anisotropic exponential type repulsive term, which is less steep than the conventional Lennard–Jones type potential.

scholarly journals Popular Integration Grids Can Result in Large Errors in DFT-Computed Free Energies

2019 ◽  
Author(s):  
Andrea N. Bootsma ◽  
Steven Wheeler
Keyword(s):  
Transition State ◽  
Molecular Orientation ◽  
Density Functional ◽  
Basis Sets ◽  
Free Energies ◽  
Functional Theory ◽  
Metal Free ◽  
Stereoselective Reactions ◽  
Functionalization Reaction ◽  
Transition State Structures

<div>Density functional theory (DFT) has emerged as a powerful tool for analyzing organic and organometallic systems and proved remarkably accurate in computing the small free energy differences that underpin many chemical phenomena (e.g. regio- and stereoselective reactions). We show that the lack of rotational invariance of popular DFT integration grids reveals large uncertainties in computed free energies for isomerizations, torsional barriers, and regio- and stereoselective reactions. The result is that predictions based on DFT-computed free energies for many systems can change qualitatively depending on molecular orientation. For example, for a metal-free propargylation of benzaldehyde, predicted enantioselectivities based on B97-D/def2-TZVP free energies using the popular (75,302) integration grid can vary from 62:38 to 99:1 by simply rotating the transition state structures. Relative free energies for the regiocontrolling transition state structures for an Ir-catalyzed C–H functionalization reaction computed using M06/6-31G(d,p)/LANL2DZ and the same grid can vary by more than 5 kcal/mol, resulting in predicted regioselectivities that range anywhere from 14:86 to >99:1. Errors of these magnitudes occur for different functionals and basis sets, are widespread among modern applications of DFT, and can be reduced by using much denser integration grids than commonly employed.</div>

An ab initio study on the reaction of CH(X2π) with CH4

1993 ◽  
Vol 71 (4) ◽  
pp. 512-519 ◽  
Author(s):  
Zhonghua Yu ◽  
Congxiang Chen ◽  
Mingbao Huang
Keyword(s):  
Ab Initio ◽  
Correlation Energy ◽  
Reaction Path ◽  
Addition Reaction ◽  
High Energy ◽  
Insertion Reaction ◽  
Molecular Orbital Calculations ◽  
Configuration Interaction Method ◽  
State Abstraction ◽  
Moller Plesset

The mechanism of the reaction CH(X2π) + CH4 has been investigated by ab initio molecular orbital calculations. Addition, insertion, and abstraction–addition reaction paths have been examined by, in total, five methods of approach. The addition reaction path has a rather high energy barrier. Our calculations have implied that the assumed insertion reaction path does not seem to exist for the reaction CH + CH4, and a two-step mechanism (abstraction–addition reaction path) was then proposed. For the abstraction–addition reaction, the reactants, transition state, intermediates, and products were optimized at the HF/3-21G and HF/6-31G* levels, and vibrational frequencies were calculated at the HF/3-21G level. Electronic correlation energy was estimated by means of the Møller–Plesset perturbation theory and configuration interaction method. The excited-state abstraction reaction was also studied in some detail.

scholarly journals Mechanisms and consequences of oxygen transfer reactions

2000 ◽  
Vol 72 (12) ◽  
pp. 2259-2264 ◽  
Author(s):  
Peter Beak ◽  
David R. Anderson ◽  
Stephen G. Jarboe ◽  
Mitchell L. Kurtzweil ◽  
Keith W. Woods
Keyword(s):  
Double Bond ◽  
Transition State ◽  
Molecular Oxygen ◽  
Oxygen Transfer ◽  
Large Angle ◽  
Transfer Reactions ◽  
Oblique Angle ◽  
Leaving Groups ◽  
Transition State Structures

The geometry about oxygen in the transition-state structures for oxygen transfers from a nitrone to phosphorous, from a percarboxylic acid to a carbon­carbon double bond, and from an N-sulfonyl oxaziridine to a carbon­carbon double bond have been evaluated by the endocyclic restriction test. The former can proceed at an oblique angle, while the latter two require a large angle between the entering and leaving groups on oxygen. This information is used to determine the mechanism of the aldehyde-dependent oxygen transfer from molecular oxygen to a carbon­carbon double bond.

scholarly journals Popular Integration Grids Can Result in Large Errors in DFT-Computed Free Energies

2019 ◽  
Author(s):  
Andrea N. Bootsma ◽  
Steven Wheeler
Keyword(s):  
Transition State ◽  
Molecular Orientation ◽  
Density Functional ◽  
Basis Sets ◽  
Free Energies ◽  
Functional Theory ◽  
Metal Free ◽  
Stereoselective Reactions ◽  
Functionalization Reaction ◽  
Transition State Structures

Density functional theory (DFT) has emerged as a powerful tool for analyzing organic and organometallic systems and proved remarkably accurate in computing the small free energy differences that underpin many chemical phenomena (e.g. regio- and stereoselective reactions). We show that the lack of rotational invariance of popular DFT integration grids reveals large uncertainties in computed free energies for some isomerizations, torsional barriers, and regio- and stereoselective reactions. The result is that predictions based on DFT-computed free energies for many systems can change qualitatively depending on molecular orientation. For example, for a metal-free propargylation of benzaldehyde, predicted enantioselectivities based on B97-D/def2-TZVP free energies using the popular (75,302) integration grid can vary from 62:38 to 99:1 by simply rotating the transition state structures. Relative free energies for the regiocontrolling transition state structures for an Ir-catalyzed C–H functionalization reaction computed using M06/6-31G(d,p)/LANL2DZ and the same grid can vary by more than 5 kcal/mol, resulting in predicted regioselectivities that range anywhere from 14:86 to >99:1. Errors of these magnitudes occur for different functionals and basis sets, are potentially widespread among modern applications of DFT, and can be reduced by using much denser integration grids than commonly employed.<br>

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