NEW REACTION PATHWAYS OF PROPENE + BCl3 DECOMPOSITION IN CHEMICAL VAPOR DEPOSITION PROCESS

2012 ◽  
Vol 11 (01) ◽  
pp. 53-85 ◽  
Author(s):  
JIANHUA YANG ◽  
KEHE SU ◽  
YAN LIU ◽  
YANLI WANG ◽  
QINGFENG ZENG ◽  
...  
Keyword(s):  
Density Functional ◽  
Chemical Vapor ◽  
Deposition Process ◽  
Reaction Pathways ◽  
Electronic Correlation ◽  
Free Energies ◽  
Functional Theory ◽  
Reaction Coordinates ◽  
The Density Functional Theory ◽  
Correct Reaction

More reaction pathways in the CVD process of preparing boron-carbides with BCl3-C3H6(propene)-H2 precursors were examined in addition to the "lowest" path proposed by Jiang et al. in Theor Chem Acc127:519–538, 2010. The new pathways investigated in this work involve 81 new transition states and 79 new intermediates. Geometries of the species were optimized with the density functional theory at B3PW91/6-311G(d,p) level. Intrinsic reaction coordinates were analyzed to confirm the correct reaction linkages. Energy barriers and reaction energies were calculated with the accurate model chemistry method G3(MP2) after a non-dynamical electronic correlation detection using CASSCF method. Heat capacities and entropies were obtained with the statistical thermodynamics and fitted as a function of temperature. Gibbs free energies at 298.15 K and 1200 K were used to examine the reaction paths. It was found that some steps in the new paths at both 298.15 K and 1200 K are different from the "lowest" path obtained previously and the pathways for the new products CB and C2B were obtained.

scholarly journals THEORETICAL STUDY ON THE REACTION MECHANISM OF CO2 FORMATION FROM ACYLOXY RADICALS

2018 ◽  
Vol 55 (6A) ◽  
pp. 105
Author(s):  
Nguyen Thi Minh Hue
Keyword(s):  
Reaction Mechanism ◽  
Density Functional ◽  
Basis Sets ◽  
Free Energies ◽  
Combustion Chemistry ◽  
Functional Theory ◽  
Mechanism Of Decomposition ◽  
Energy Profiles ◽  
The Density Functional Theory ◽  
Experimental Values

The decomposition mechanism of acyloxy radicals has been studied by the Density Functional Theory (DFT) using B3LYP functional in conjunction with the 6-311++G(d,p) and 6-311++G(3df,2p) basis sets. The potential energy profiles for reaction systems were generally established. Calculated results indicate that the formation of products including hydrocarbon radicals and CO2 molecule is energetically favored. The rate of decomposition increases with the number of carbon in non-cyclic saturated acyloxy radicals. Calculated enthalpies and Gibbs free energies of reactions well agree with experimental values. This study is a contribution to the understanding of the reaction mechanism of decomposition of acyloxy radicals in atmosphere and combustion chemistry. 

scholarly journals Substituição nucleofílica alifática: qual o mecanismo preferencial? Estudo computacional dos efeitos da estrutura do substrato e solvente

2020 ◽  
Author(s):  
Bárbara Pereira Peixoto ◽  
José Walkimar de M. Carneiro ◽  
Rodolfo Goetze Fiorot
Keyword(s):  
Density Functional ◽  
Reaction Pathway ◽  
Computational Method ◽  
Reaction Pathways ◽  
Substitution Reactions ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
High Dielectric ◽  
Energy Reaction ◽  
Bimolecular Mechanism

Nucleophilic aliphatic substitution reactions constitute important steps in the synthesis of substances with biological activity and industrial appeal, beyond to participating in steps in biosynthetic routes of natural products. Unimolecular (SN1) and bimolecular (SN2) pathways can be understood as limiting cases of a mechanistic continuum. In between them, borderline mechanisms are proposed. The preference for one path over another depends on several factors, such as the structure of the substrate, the nucleophile and the solvent used. This plurality is still a topic of discussion and needs further understanding. In this context, the present work aims to rationalize the preferential reaction pathway for nucleophilic aliphatic substitutions, whose substrates do not fit only in the uni- and bimolecular models, by identifying lower energy reaction pathways due to the structural and electronic characteristics. The evaluation was carried out by molecular modeling at the Density Functional Theory (DFT) level, simulating substrates with the nucleofuge (Cl and NH3 + ) connected to secondary carbon atoms, with the computational method M06-2X/aug-cc-pVTZ, previously validated according to geometrical and energetic parameters. Besides, we checked the effect of a polar solvent with high dielectric constant in the reaction pathways. The analyzed substrates demonstrated preference for the bimolecular mechanism and the influence of a solvent in these reactions was evident.

scholarly journals Low-Temperature Polymorphic Transformation of β-Lactam Antibiotics

Crystals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 460
Author(s):  
Luo ◽  
Liu ◽  
He ◽  
Li
Keyword(s):  
Low Temperature ◽  
Density Functional ◽  
Polymorphic Transformation ◽  
Ab Initio Method ◽  
Free Energies ◽  
Functional Theory ◽  
Research Areas ◽  
The Density Functional Theory ◽  
Drug Storage ◽  
Moller Plesset

Abstract: Polymorphic screening and transformation of molecular crystals are presently popular research areas in pharmaceutical studies. In this study, we developed an ab initio method to examine the structures, spectra, and stabilities of β-lactam (trans-13-azabicyclo[10.2.0]tetradecan-14-one), an important component of antibiotics. Based on the density functional theory (DFT) and second-order Møller-Plesset perturbation (MP2) methods, the present work demonstrated that forms I and II have isomorphic structures but can be distinguished by their Gibbs free energies and vibrational spectra. Forms I and II show a low-temperature polymorphic transformation at 308 K, where form I is stable below 308 K and form II is stable above 308 K. The proposed method suggests that the theoretical calculation can be used as a tool to effectively distinguish the isomorphic structures, and temperature-induced polymorphic transformation has far-reaching significance for drug storage and design.

First-principles study of intrinsic defects in CdO

2018 ◽  
Vol 32 (06) ◽  
pp. 1850059 ◽  
Author(s):  
V. P. Zhukov ◽  
N. I. Medvedeva ◽  
V. N. Krasilnikov
Keyword(s):  
Density Functional ◽  
Oxygen Vacancies ◽  
Cadmium Oxide ◽  
Metallic Phase ◽  
Hydrogen Atmosphere ◽  
Free Energies ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Metallic Cadmium ◽  
P Type

Using the density functional theory (DFT) in the GGA and LSDA + U approximations, we studied the effect of cadmium atoms in the interstitial sites and vacancies in the oxygen and cadmium sublattices on the electronic structure of rock-salt cadmium oxide (CdO). Migration of cadmium atoms into interstitial sites was shown to be unlikely. In the presence of oxygen vacancies, the behavior of CdO remains semiconducting and nonmagnetic. Cadmium vacancies induce d0 ferromagnetism and spin-dependent conductivity, which is semiconducting for spin-up electrons and is p-type metallic for spin-down electrons. The formation energies and free energies were calculated for oxygen vacancies and metallic cadmium phase, which allowed an explanation to be offered for the large number of vacancies and the metallic phase formed during reduction in hydrogen atmosphere.

Density functional theory studies of methanol adsorption and decomposition mechanism on Al13 clusters

2014 ◽  
Vol 92 (4) ◽  
pp. 293-298 ◽  
Author(s):  
Cai-Chao Ye ◽  
Feng-Qi Zhao ◽  
Si-Yu Xu ◽  
Xue-Hai Ju
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Reaction Pathways ◽  
Bond Dissociation Energies ◽  
Generalized Gradient ◽  
Aluminum Clusters ◽  
Functional Theory ◽  
Dissociation Energies ◽  
Generalized Gradient Approximation ◽  
The Density Functional Theory

The adsorption and decomposition of the CH3OH molecule on Al13 clusters were investigated by generalized gradient approximation of the density functional theory. The strong attractive forces between the CH3OH molecule and aluminum atoms induce the breaking of the H–O and C–O bonds of CH3OH. Subsequently, the dissociated CH3O and OH radical fragments oxidize the aluminum clusters. The largest adsorption energy is –205.4 kJ/mol. We also investigated five reaction pathways of the CH3OH molecule on the Al13 clusters. The activation energies are in the range of 10.3−113.1 kJ/mol. Compared with the bond dissociation energies of the C–O and O–H bonds in the isolated methanol, Al13 performs very well in decreasing the bond break barrier of CH3OH. In addition, although the C–O bond is slightly weaker than the O−H bond, the O−H bond is even easier to decompose on the Al13 surface. The rate constants of five adsorption paths over the temperature range 300−700 K are presented.

Thermodynamic Stability of Hexagonal and Rhombohedral Bn at Cvd Conditions from Van der Waals Corrected First Principles Calculations

2019 ◽  
Author(s):  
Henrik Pedersen ◽  
Björn Alling ◽  
Hans Högberg ◽  
Annop Ektarawong
Keyword(s):  
Thin Films ◽  
Thermodynamic Stability ◽  
First Principles ◽  
Thermal Equilibrium ◽  
Density Functional ◽  
Van Der Waals ◽  
Chemical Vapor ◽  
First Principles Calculations ◽  
Functional Theory ◽  
The Stability

Thin films of boron nitride (BN), particularly the sp<sup>2</sup>-hybridized polytypes hexagonal BN (h-BN) and rhombohedral BN (r-BN) are interesting for several electronic applications given band gaps in the UV. They are typically deposited close to thermal equilibrium by chemical vapor deposition (CVD) at temperatures and pressures in the regions 1400-1800 K and 1000-10000 Pa, respectively. In this letter, we use van der Waals corrected density functional theory and thermodynamic stability calculations to determine the stability of r-BN and compare it to that of h-BN as well as to cubic BN and wurtzitic BN. We find that r-BN is the stable sp<sup>2</sup>-hybridized phase at CVD conditions, while h-BN is metastable. Thus, our calculations suggest that thin films of h-BN must be deposited far from thermal equilibrium.

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