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.

scholarly journals An ab initio study on the insertion reactions of CH [X2II] with NH3, H2O, and HF

1996 ◽  
Vol 74 (6) ◽  
pp. 910-917 ◽  
Author(s):  
Zhi-Xiang Wang ◽  
Ruo-Zhuang Liu ◽  
Ming-Bao Huang ◽  
Zhonghua Yu
Keyword(s):  
Ab Initio ◽  
Electron Correlation ◽  
Lower Energy ◽  
Energy Surface ◽  
Molecular Orbital Calculations ◽  
Ab Initio Study ◽  
Insertion Reactions ◽  
Moller Plesset ◽  
Ch Radical ◽  
Water Hydrogen

The mechanisms of the reactions of CH (X2II) with NH3, H2O, and HF have been studied by means of ab initio molecular orbital calculations incorporating electron correlation with Møller–Plesset perturbation theory up to the second order. For each of the three CH reactions, the insertion path has been found in the potential energy surface; in the calculated insertion path there exists an intermediate complex prior to the transition state that has a lower energy than the reactants. Energetic results indicate that insertion paths are favourable channels for these CH reactions, which is in line with proposals based on kinetic experiments. Key words: CH radical, ammonia, water, hydrogen fluoride, reaction mechanism.

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.

Rearrangement of the Fulminate Anion (CNO-) to the Cyanate Anion (OCN-). Possible Intermediacy of the Oxazirinyl Anion

1986 ◽  
Vol 39 (6) ◽  
pp. 913 ◽  
Author(s):  
WK Li ◽  
J Baker ◽  
L Radom
Keyword(s):  
Gas Phase ◽  
Electron Correlation ◽  
Basis Set ◽  
Intramolecular Rearrangement ◽  
Molecular Orbital Calculations ◽  
Potential Well ◽  
Electron Loss ◽  
Diffuse Function ◽  
Moller Plesset ◽  
High Level

The rearrangement of the fulminate anion (CNO-) to the cyanate anion (OCN-) has been examined by using high-level ab initio molecular orbital calculations which include a diffuse-function-augmented polarization basis set and electron correlation incorporated at the full fourth-order Moller-Plesset level (MP4). The reaction is predicted to be exothermic by 275 kJ mol-1. Our best calculations indicate theinvolvement of a metastable cyclic oxazirinyl anion intermediate. However, this lies in an extremely shallow potential well and, in contrast to the predictions of semiempirical calculations, is unlikely to have more than a fleeting existence. The fulminate and cyanate anions are calculated to be stable with respect to electron loss and stable with respect to intramolecular rearrangement; accordingly, both should be observable gas-phase species.

Do the mercaptocarbene (H–C–S–H) and selenocarbene (H–C–Se–H) congeners of hydroxycarbene (H–C–O–H) undergo 1,2-H-tunneling?

2011 ◽  
Vol 76 (6) ◽  
pp. 645-667 ◽  
Author(s):  
János Sarka ◽  
Attila G. Császár ◽  
Peter R. Schreiner
Keyword(s):  
Electron Correlation ◽  
Reaction Path ◽  
Focal Point ◽  
Structural Data ◽  
Basis Sets ◽  
Stationary Points ◽  
One Dimensional ◽  
Point Analysis ◽  
Uncertainty Estimates

The principal purpose of this investigation is the determination of the tunneling half-lives of the trans-HCSH → H2CS and the trans-HCSeH → H2CSe unimolecular isomerization reactions at temperatures close to 0 K. To aid these determinations, accurate electronic structure computations were performed, with electron correlation treatments as extensive as CCSDT(Q) and basis sets as large as aug-cc-pCV5Z, for the isomers of [H,H,C,S] and [H,H,C,Se] on their lowest singlet surfaces and for the appropriate transition states yielding structural data for key stationary points characterizing the isomerization reactions. The computational results were subjected to a focal-point analysis (FPA) that yields accurate relative energies with uncertainty estimates. The tunneling half-lives were determined by a simple Eckart-barrier approach and via the more sophisticated though still one-dimensional Wentzel–Kramers–Brillouin (WKB) approximation. Only stationary-point information is needed for the former while an intrinsic reaction path (IRP) is necessary for the latter approach. Both protocols suggest that, unlike for the parent hydroxymethylene (HCOH), at the low temperatures of matrix isolation experiments no tunneling will be observable for the trans-HCSH and trans-HCSeH systems.

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.

A theoretical insight into the insertion reaction of singlet methylene to the hydrogen molecule

1987 ◽  
Vol 65 (9) ◽  
pp. 1995-1999 ◽  
Author(s):  
M. Ortega ◽  
J. M. Lluch ◽  
A. Oliva ◽  
J. Bertran
Keyword(s):  
Hydrogen Molecule ◽  
Energy Surface ◽  
Correlation Energy ◽  
Geometry Optimization ◽  
Direct Consequence ◽  
Electronic Configuration ◽  
Basis Set ◽  
Insertion Reaction ◽  
Moller Plesset ◽  
Singlet Methylene

The least-motion and non-least-motion energy profiles for the insertion reaction of singlet methylene into the hydrogen molecule have been calculated using the 6-31G* basis set and introducing the correlation energy with the Møller–Plesset perturbation theory and with the MC-SCF technique. From the results obtained the effect of geometry optimization including electron correlation on the shape of the energy surface is discussed. The building up of a bidimensional biconfigurational energy surface has permitted one to interpret the opening of the methylene angle during the least-motion process as a direct consequence of the change in the electronic configuration. The TC-SCF/6-31G* second order transition structure for this forbidden process has been directly located using gradient minimization methods.

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.

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