Formation of β-O-4 Lignin Models -A Theoretical Study

Holzforschung ◽  
2003 ◽  
Vol 57 (5) ◽  
pp. 466-478 ◽  
Author(s):  
B. Durbeej ◽  
L. A. Eriksson
Keyword(s):  
Reaction Mechanisms ◽  
Density Functional Calculations ◽  
Energy Barrier ◽  
Density Functional ◽  
Theoretical Study ◽  
Coniferyl Alcohol ◽  
Quinone Methide ◽  
Reaction Energy ◽  
Alcohol Radical

Summary The formation of two different β-O-4 lignin models is investigated by means of density functional calculations. It is found that the coupling of two coniferyl alcohol radicals forming a quinone methide proceeds by an energy barrier of ~2–5 kcal/mol, and that the associated reaction energy is negative by more than 20 kcal/mol. On the basis of the corresponding results obtained for the coupling of a coniferyl alcohol radical to a coniferyl alcohol, it is argued that the resulting radical, albeit being formed in an energetically less favourable process, might play an important role in lignin polymerisation. Finally, two different reaction mechanisms for the conversion of a quinone methide into a guaiacylglycerol-β-coniferyl ether dilignol through the addition of water are explored.

A DFT study on the mechanism of reaction between 2, 4-diisocyanatotolune and cellulose

2016 ◽  
Vol 15 (02) ◽  
pp. 1650012 ◽  
Author(s):  
Jiping Cao ◽  
Yali Liu ◽  
Aijuan Shi ◽  
Yuan Yuan ◽  
Mingliang Wang
Keyword(s):  
Reaction Mechanisms ◽  
Energy Barrier ◽  
Density Functional ◽  
Membered Ring ◽  
Functional Theory ◽  
Mechanism Of Reaction ◽  
The Density Functional Theory ◽  
Good Accordance ◽  
Experimental Activation Energy ◽  
Ring Transition State

The reaction mechanisms between 2, 4-Diisocyanatotolune (2, 4-TDI) and cellulose have been investigated using the density functional theory at the B3LYP/6-31[Formula: see text]G (d, p) level. The calculations show that the direct addition of 2, 4-TDI and cellulose possesses an unrealistically high barrier of 32–34[Formula: see text]kcal[Formula: see text]mol[Formula: see text]. With a neighboring [Formula: see text]-d-glucose serving as a proton transporter by forming a flexible six-membered ring transition state, the energy barrier of the reaction is significantly reduced to 16–18 kcal[Formula: see text]mol[Formula: see text], which is in a good accordance with the experimental activation energy of 13.9–16.7[Formula: see text]kcal[Formula: see text]mol[Formula: see text]. It is indicated that the reaction between 2, 4-TDI and cellulose is auto-catalyzed with a neighboring [Formula: see text]-d-glucose acting as a reactive catalyst.

scholarly journals Theoretical Study on Influence of Cobalt Oxides Valence State Change for C6H5COOH Pyrolysis

Catalysts ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 197
Author(s):  
Si-Mei Fu ◽  
Yue Zhao ◽  
Jiang-Tao Liu ◽  
Wen-Sheng Liang ◽  
Gang-Sen Li ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Valence State ◽  
Energy Barrier ◽  
Density Functional ◽  
Model Compound ◽  
Theoretical Study ◽  
Cobalt Oxides ◽  
State Change ◽  
Pyrolysis Process ◽  
Functional Theory

Benzoic acid (C6H5COOH) is selected as coal-based model compound with Co compounds (Co3O4, CoO and Co) as the catalysts, and the influence of the valence state change of the catalyst for pyrolysis process is investigated using density functional theory (DFT). DFT results shows that the highest energy barrier of C6H5COOH pyrolysis is in the following order: Ea(CoO) <Ea(Co3O4) <Ea(no catalyst) <Ea(Co). In general, Co3O4 catalyst accelerates C6H5COOH pyrolysis. Then, the catalytic activity further increases when Co3O4 is reduced to CoO. Finally, Co shows no activity for C6H5COOH pyrolysis due to the reduction of CoO to metallic Co.

THEORETICAL STUDY OF HYDROGEN BONDED CLUSTERS OF AMMONIA AND FULMINIC ACID

2008 ◽  
Vol 07 (02) ◽  
pp. 277-286 ◽  
Author(s):  
ABEDIEN ZABARDASTI ◽  
SAEID AMANI ◽  
MARYAM SALEHNASSAJ ◽  
ALI H. KIANFARD
Keyword(s):  
Ab Initio ◽  
Density Functional Calculations ◽  
Cluster Size ◽  
Density Functional ◽  
Theoretical Study ◽  
Cooperative Effect ◽  
Stabilization Energy ◽  
Topological Parameters ◽  
Hydrogen Bonded

Ab initio and density functional calculations are used to analyze the interaction between a molecule of fulminic acid with one, two, three, and four molecules of ammonia along with a 2:2 complex at B3LYP/6-311++G(d, p) and MP2/6-311++G(d, p) computational levels. Cooperative effect (CE) in terms of stabilization energy of clusters is calculated and discussed as well. For the studied clusters, the CE is increased with increasing cluster size. Red shifts of H – C stretching frequency for complexes involving HCNO as H -donor are predicted. Atom in molecules is used to analyze the cooperative effect on topological parameters.

A THEORETICAL STUDY OF UNSATURATED OLEFIN HYDROGENATION AND ISOMERIZATION ON Pd(111)

2008 ◽  
Vol 15 (03) ◽  
pp. 249-259 ◽  
Author(s):  
PATRICIA G. BELELLI ◽  
NORBERTO J. CASTELLANI
Keyword(s):  
Energy Barrier ◽  
Density Functional ◽  
Theoretical Study ◽  
High Energy ◽  
Slab Model ◽  
Functional Theory ◽  
Hydrogen Addition ◽  
High Energy Barrier ◽  
The Density Functional Theory ◽  
Cis And Trans

The addition of hydrogen to the carbon–carbon double bond of 2-butenes adsorbed on Pd (111) was studied within the density functional theory (DFT) and using a periodic slab model. For that purpose, the Horiuti–Polanyi mechanisms for both complete hydrogenation and isomerization were considered. The hydrogenation of cis and trans-2-butene to produce butane proceeds via the formation of eclipsed and staggered-2-butyl intermediates, respectively. In both cases, a relatively high energy barrier to produce the half-hydrogenated intermediate makes the first hydrogen addition the slowest step of the reaction. The competitive production of trans-2-butene from cis-2-butene requires the conversion from the eclipsed-2-butyl to the staggered-2-butyl isomer. As the corresponding energy barrier is relatively small and because the first of these isomers is less stable than the second, an easy conversion is predicted.

scholarly journals First-Principles Study of the Reaction between Fluorinated Graphene and Ethylenediamine

Molecules ◽  
2019 ◽  
Vol 24 (2) ◽  
pp. 284
Author(s):  
Jin Tian ◽  
Yuhong Chen ◽  
Jing Wang ◽  
Tingting Liu ◽  
Meiling Zhang ◽  
...  
Keyword(s):  
Energy Barrier ◽  
Density Functional ◽  
Population Analysis ◽  
Reaction Process ◽  
Main Reaction ◽  
Mulliken Charge ◽  
Reaction Energy ◽  
Functional Theory ◽  
Fluorinated Graphene ◽  
Trans Structure

The reaction process between gauche- and trans-structure ethylenediamine (EDA) and fluorinated graphene (CF) was studied based on density functional theory (DFT). Firstly, the reaction between the most stable gauche-structure EDA and CF was discussed. Some of the reaction results were verified in experiment, but the overall reaction energy barrier was higher. Then, the reaction between the trans-structured EDA and CF was simulated, which concluded that CF is reduced in the main reaction channel and HF is generated at the same time. In this reaction process, the reaction energy barrier is as low as 0.81 eV, which indicates that the reaction may occur spontaneously under natural conditions The Mulliken charge population analysis and the calculation of bond energy prove that the NH bond is more stable than CH and that the H atoms in the CH2 of trans-structure EDA more easily react with CF.

Reaction Mechanisms of H2 Reduction and N2O Decomposition on Fe/ZSM-5 Zeolite: A Density Functional Theoretical Study

2009 ◽  
Vol 113 (42) ◽  
pp. 18184-18190 ◽  
Author(s):  
Gang Yang ◽  
Lijun Zhou ◽  
Xianchun Liu ◽  
Xiuwen Han ◽  
Xinhe Bao
Keyword(s):  
Reaction Mechanisms ◽  
Density Functional ◽  
Theoretical Study ◽  
N2o Decomposition ◽  
Zeolite A

Effect of the Kerogen Molecular Structure on the Formation of Methane During Kerogen Pyrolysis

2019 ◽  
Vol 72 (3) ◽  
pp. 174 ◽  
Author(s):  
Qing Wang ◽  
Xinmin Wang ◽  
Shuo Pan
Keyword(s):  
Hydrogen Atom ◽  
Energy Barrier ◽  
Density Functional ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Reaction Energy ◽  
Hydrogen Atoms ◽  
Energy Barriers ◽  
Kerogen Pyrolysis ◽  
Intramolecular Hydrogen

In this study, density functional theory (DFT) at the GGA/RPBE level was employed to examine the effects of the kerogen microstructure on the formation mechanism of methane during the pyrolysis of kerogen. The calculations prove that the evolution of CH4 during kerogen pyrolysis corresponds to demethylation, and the process of forming methane involves the interaction of intramolecular hydrogen atom transfer and assistant hydrogen atom transfer. In all reaction paths, the energy barrier of path 5 is the smallest at 260.56kJmol−1. The energy barrier of path 6 is the largest at 554.36kJmol−1. The results indicate that CO is favourable for demethylation, and CO2 is not conducive to demethylation. Path 1 is the formation of methane by the transfer of assistant hydrogen atoms, and the required energy barrier is 379.45kJmol−1. The side chain structure of the aromatic hydrocarbon structure is liable to demethylation to form methane. A comparison of the reaction energy barriers follows the order: path 1&lt;path 15&lt;path 14&lt;path 10, which indicates the that difference in the demethylation reaction is based on the microstructure. In the same reaction process, the benzene ring and the aliphatic hydrocarbon structure are more susceptible to demethylation to form methane. In the heterocyclic bicyclic structures containing O and S, a comparison of the reaction energy barriers follows the order: path 11 ≈ path 12&lt;path 13, so paths 11 and 12 are close, but path 13 is more difficult to occur, indicating that it is more difficult to demethylate with heteroatoms in the same ring. From a thermodynamic point of view, in the process of assisting the formation of methane by hydrogen atoms, the demethylation reaction is mainly an endothermic reaction. During the transfer of intramolecular hydrogen atoms, the demethylation reaction is mainly an exothermic reaction, and most reactions are spontaneous.

COMPUTATIONAL STUDIES OF THE AMMONOLYSIS FOR N-METHYL β-SULTAM

2005 ◽  
Vol 04 (02) ◽  
pp. 383-395
Author(s):  
MAOXIA HE ◽  
DACHENG FENG ◽  
JU XIE ◽  
ZHENGTING CAI
Keyword(s):  
Energy Barrier ◽  
Density Functional ◽  
Dft Method ◽  
Computational Studies ◽  
Reaction Energy ◽  
Positive Role ◽  
Functional Theory ◽  
Concerted Mechanism ◽  
Alcoholysis Reaction ◽  
Reaction Processes

As a first step toward the understanding of the aminolysis reaction of β-sultam compounds, the ammonolysis and the effect of a second ammonia on the ammonolysis reactions of N -methyl β-sultam have been studied using Density Functional Theory (DFT) method at the B3LYP/6-31G* level. The exploration of the reaction processes proposed two different mechanisms: concerted and stepwise mechanisms. There is one pathway in concerted mechanism and two pathways in stepwise mechanisms: pathways a and b. The calculations of reaction energy barriers show that the nonconcerted route is the more favored one. Solvent effects were assessed by the PCM method. The results show that the pathway a in channel II is the most favorable in both cases. The presence of solvent disfavors the reaction, and the participation of ammonia in the ammonolysis reaction plays a positive role and reduces the active energy greatly. All transition states in the assisted ammonolysis are 45–65 kJ/mol lower than those for the non-assisted reaction. The results also show that the ammonolysis reaction have a higher energy barrier than the alcoholysis reaction. This low reactivity of amines is also observed in the reactions of N -benzoyl β-sultam and p-nitrophenyl toluene-p-sulfonate where there is a distinct preference towards oxygen nucleophiles.

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