Mechanistic study of methanol oxidation by RuIV–oxo complexes

2015 ◽  
Vol 19 (01-03) ◽  
pp. 417-426
Author(s):  
Yoshihito Shiota ◽  
Shoya Takahashi ◽  
Shingo Ohzu ◽  
Tomoya Ishizuka ◽  
Takahiko Kojima ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Methanol Oxidation ◽  
Density Functional ◽  
Activation Barrier ◽  
Hydrogen Abstraction ◽  
Hydroxyl Group ◽  
Mechanistic Study ◽  
Activation Barriers ◽  
Bond Dissociation ◽  
Oxo Complexes

The catalytic conversion of methanol to formaldehyde by three kinds of non-porphyrin Ru complexes, Ru IV O ( TPA ) (TPA = tris(2-pyridylmethyl)amine) (1a), Ru IV O (6- COO - TPA ) (6-COO-TPA = 2-(6-carboxyl-pyridyl)methyl-bis(2-pyridylmethyl)amine) (1b), and Ru IV O ( N4Py ) (N4Py = N,N-bis(2-pyridyl-methyl)-N-bis(2-pyridyl)methylamine) (1c), is discussed by using density functional theory (DFT) calculations. There are two possible reaction pathways for the oxidation of methanol to formaldehyde with respect to the first hydrogen abstraction from the methyl group (path 1) and the hydroxyl group (path 2). Path 1 and path 2 involve the hydroxymethyl radical (• CH 2 OH ) and the methoxyl radical ( CH 3 O •), respectively, as an intermediate. DFT calculations demonstrate that the two pathways are energetically comparable in the reactions by the three Ru IV –oxo complexes. The reactions with 1a and 1c are initiated by the C – H bond dissociation with activation barriers of 22.2 and 21.4 kcal/mol, respectively, while the reaction with 1b is initiated by the O – H bond dissociation with an activation barrier of 18.1 kcal/mol. However, the calculations showed that the rate-determining step is the H -atom abstraction from the CH 3 group of methanol in all the pathways. These results are in good agreement with kinetic analysis of the reactions by the Ru IV –oxo complexes, being useful for considering the mechanism of methanol oxidation.

Mechanistic Study on Gold(I)-Catalyzed Unsaturated Spiroketalization Reaction

2022 ◽  
Vol 19 ◽  
Author(s):  
Kamlesh Sharma
Keyword(s):  
Activation Barrier ◽  
Ring Formation ◽  
Hydroxyl Group ◽  
Mechanistic Study ◽  
Protecting Group ◽  
Wide Range ◽  
Oxocarbenium Ion ◽  
Metal Catalyzed ◽  
Insight Into ◽  
Mechanism Of The Reaction

Abstract: The mechanism of metal-catalyzed spiroketalization of propargyl acetonide is explored by employing DFT with the B3LYP/6-31+G(d) method. Acetonide is used as a regioselective regulator in the formation of monounsaturated spiroketal. The energies of transition states, intermediates, reactants and products are calculated to provide new insight into the mechanism of the reaction. The energetic features, validation of the observed trends in regioselectivity are conferred in terms of electronic indices via FMO analysis. The presence of acetonide facilitates a stepwise spiroketalization as it masks the competing nucleophile, and thus hydroxyl group present, exclusively acts as a nucleophile. The vinyl gold intermediate 3 is formed from 2 via activation barrier TS1. This is the first ring formation, which is 6-exo-dig cyclization. The intermediate 3 is converted into allenyl ether 4, which isomerizes to the intermediate oxocarbenium ion 5 via activation barrier TS2. The intermediate 5 cyclizes to 6 via TS3. This is the second ring formation. The intermediate 6 on protodeauration turns into 6,6-monounsaturated spiroketal 7. It is concluded that acetonide as a protecting group serves the purpose, and thus a wide range of spiroketals can be prepared, regioselectivity.

scholarly journals Flavones’ and Flavonols’ Antiradical Structure–Activity Relationship—A Quantum Chemical Study

Antioxidants ◽  
2020 ◽  
Vol 9 (6) ◽  
pp. 461 ◽  
Author(s):  
Maciej Spiegel ◽  
Tadeusz Andruniów ◽  
Zbigniew Sroka
Keyword(s):  
Electron Transfer ◽  
Hydrogen Bonding ◽  
Density Functional ◽  
Hydrogen Abstraction ◽  
Quantum Chemical Study ◽  
Hydrogen Atom Transfer ◽  
Hydroxyl Group ◽  
Water Solvent ◽  
Intramolecular Hydrogen ◽  
Catechol Moiety

Flavonoids are known for their antiradical capacity, and this ability is strongly structure-dependent. In this research, the activity of flavones and flavonols in a water solvent was studied with the density functional theory methods. These included examination of flavonoids’ molecular and radical structures with natural bonding orbitals analysis, spin density analysis and frontier molecular orbitals theory. Calculations of determinants were performed: specific, for the three possible mechanisms of action—hydrogen atom transfer (HAT), electron transfer–proton transfer (ETPT) and sequential proton loss electron transfer (SPLET); and the unspecific—reorganization enthalpy (RE) and hydrogen abstraction enthalpy (HAE). Intramolecular hydrogen bonding, catechol moiety activity and the probability of electron density swap between rings were all established. Hydrogen bonding seems to be much more important than the conjugation effect, because some structures tends to form more intramolecular hydrogen bonds instead of being completely planar. The very first hydrogen abstraction mechanism in a water solvent is SPLET, and the most privileged abstraction site, indicated by HAE, can be associated with the C3 hydroxyl group of flavonols and C4’ hydroxyl group of flavones. For the catechol moiety, an intramolecular reorganization to an o-benzoquinone-like structure occurs, and the ETPT is favored as the second abstraction mechanism.

scholarly journals An Accurate and Efficient Method to Predict Y-NO Bond Homolysis Bond Dissociation Energies

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Hong Zhi Li ◽  
Lin Li ◽  
Zi Yan Zhong ◽  
Yi Han ◽  
LiHong Hu ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Density Functional ◽  
Molecular Descriptors ◽  
Basis Set ◽  
Bond Dissociation Energies ◽  
Data Set ◽  
Test Set ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Bond Homolysis

The paper suggests a new method that combines the Kennard and Stone algorithm (Kenstone, KS), hierarchical clustering (HC), and ant colony optimization (ACO)-based extreme learning machine (ELM) (KS-HC/ACO-ELM) with the density functional theory (DFT) B3LYP/6-31G(d) method to improve the accuracy of DFT calculations for the Y-NO homolysis bond dissociation energies (BDE). In this method, Kenstone divides the whole data set into two parts, the training set and the test set; HC and ACO are used to perform the cluster analysis on molecular descriptors; correlation analysis is applied for selecting the most correlated molecular descriptors in the classes, and ELM is the nonlinear model for establishing the relationship between DFT calculations and homolysis BDE experimental values. The results show that the standard deviation of homolysis BDE in the molecular test set is reduced from 4.03 kcal mol−1calculated by the DFT B3LYP/6-31G(d) method to 0.30, 0.28, 0.29, and 0.32 kcal mol−1by the KS-ELM, KS-HC-ELM, and KS-ACO-ELM methods and the artificial neural network (ANN) combined with KS-HC, respectively. This method predicts accurate values with much higher efficiency when compared to the larger basis set DFT calculation and may also achieve similarly accurate calculation results for larger molecules.

scholarly journals Density functional theory (DFT) calculations of conformational energies and interconversion pathways in 1,2,7-thiadiazepane

2011 ◽  
Vol 76 (3) ◽  
pp. 395-406 ◽  
Author(s):  
Mina Haghdadi ◽  
Nahid Farokhi
Keyword(s):  
Density Functional Theory ◽  
Dft Calculations ◽  
Density Functional ◽  
Activation Barrier ◽  
Stable Conformer ◽  
Functional Theory ◽  
Conformational Interconversion ◽  
Interconversion Barrier ◽  
The One ◽  
Twist Boat

The molecular structure and conformational analysis of 1,2,7-thiadiazapane conformers were investigated by density functional theory (DFT) calculations at the B3LYP/cc-pVDZ level of theory. Four twist-chair (TC), six twist-boat (TB), two boat (B), two chair (C) and four twist (T) conformers were identified as minima and transition states for 1,2,7-thiadiazepane. The TC1 conformer is the most stable conformer and the twist-chair conformers are predicted to be lower in energy than their corresponding boat and chair conformations. DFT predicts a small barrier to pseudo-rotation and a remarkable activation barrier for the conformational interconversion of the twist-chair conformers to their corresponding boat conformers. The simplest conformational process and the one with the lowest barrier is the degenerate interconversion of the twist-chair 3 (TC3) conformation with itself via the CS symmetric chair (C2) transition state. The calculated strain energy barrier for this process is 2.41 kJ mol-1. The highest conformational interconversion barrier is between TC2 and twistboat 3 (TB3) forms, which was found to be 75.62 kJ mol-1.

Facile formation of azines from reactions of singlet methylene and dimethylcarbene with precursor diazirines: theoretical explorations

1999 ◽  
Vol 77 (5-6) ◽  
pp. 540-549 ◽  
Author(s):  
Gennady V Shustov ◽  
Michael TH Liu ◽  
K N Houk
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Ring Opening ◽  
Density Functional ◽  
Activation Barrier ◽  
Thermal Reaction ◽  
Orbital Theory ◽  
Functional Theory ◽  
Activation Barriers ◽  
Singlet Methylene

The reactions of the singlet methylene (1a) and dimethylcarbene (1b), with their diazirine precursors, diazirine (2a), and dimethyldiazirine (2b), have been studied theoretically using ab initio and density functional theory. The reaction has no activation barriers for the parent system (1a + 2a) and proceeds via a reactive complex and a transition state with a small negative enthalpy of activation Δ Hnot =298 = -1.1 kcal mol-1, ΔSnot =298 = -34.4 cal mol-1 K-1, ΔG°298 = 9.2 kcal mol-1) for the dimethyl derivatives (1b + 2b). The formation of N-methylene diazirinium ylides (3a,b) is exothermic by 64-80 kcal mol-1. The isomer, 1,3-diazabicyclo[1.1.0]butane (4a), is more stable (5-12 kcal mol-1) than isomer 3a, but can neither be formed by direct thermal reaction of 1a with 2a nor undergo the direct rearrangement into formaldazine (5a). The rearrangement of ylides 3a,b into azines 5a,b proceeds by conrotatory C3-N1 ring opening. The predicted activation barrier of ca. 15 kcal mol-1 for the ring opening in ylide 3b is in excellent agreement with experimental data. The formation of pyridinium ylides from carbenes and pyridine is also studied.Key words: diazirinium ylide, ab initio MO (molecular orbital) theory, density functional theory, pyridinium ylide, CIS (singles configuration interaction) transition energies.

scholarly journals Theoretical study of dimethylcarbonate production by urea alcoholysis

2020 ◽  
Vol 62 (4) ◽  
pp. 38-50
Author(s):  
Nikita I. Kurshev ◽  
Keyword(s):  
Zinc Oxide ◽  
Density Functional ◽  
Dimethyl Carbonate ◽  
Activation Barrier ◽  
Equilibrium Constants ◽  
Density Functional Method ◽  
Intermediate Formation ◽  
Functional Method ◽  
Activation Barriers ◽  
The Difference

Using the density functional method М06, the mechanisms of non-catalytic reactions of transesterification of urea with methanol with the formation of dimethyl carbonate, as well as in catalysis with zinc oxide and acetate, were studied. The transesterification proceeds stepwise with the intermediate formation of methyl carbamate. The non-catalytic process of transesterification of urea with methanol proceeds by the mechanism of nucleophilic SN2 substitution and is accompanied by the formation of pre-reaction complexes, which through synchronous transition states turn into post-reaction complexes, decomposing into ammonia and methyl carbamate in the first stage and dimethyl carbonate in the second. It has been established that methanol associates can take part in these reactions. Their participation is preferable both kinetically and thermodynamically. An analysis of the equilibrium constants of the reaction of urea with methanol at various temperatures showed that in a wide temperature range their values remain large in the first stage – the formation of methyl carbamate and become significantly reversible in the second – the conversion of methyl carbamate to dimethyl carbonate. Reactions involving acetate and zinc oxide proceed through the same stages as non-catalytic interactions. In the case of zinc acetate catalyzed reactions, if methanol monomer is involved in the reaction, the reaction of formation of methyl carbamate has a lower activation barrier compared to the reaction of conversion of methyl carbamate to dimethyl carbonate. If a methanol dimer is involved in the reaction, both reactions have a practically equal activation barrier. In the case of zinc oxide catalyzed interactions, reactions involving a methanol dimer were not detected. The participation of the catalyst leads to a significant decrease in activation barriers, and a more significant decrease occurs in the case of catalysis with zinc oxide. The reason for the different catalytic activity, in our opinion, is the difference in the charges on the urea carbon atom in the pre-reaction complexes.

scholarly journals An insight into methanol oxidation mechanisms on RuO2(100) under an aqueous environment by DFT calculations

2017 ◽  
Vol 19 (11) ◽  
pp. 7476-7480 ◽  
Author(s):  
Tian Sheng ◽  
Jin-Yu Ye ◽  
Wen-Feng Lin ◽  
Shi-Gang Sun
Keyword(s):  
Dft Calculations ◽  
Methanol Oxidation ◽  
Density Functional ◽  
Md Simulations ◽  
Water Molecules ◽  
Aqueous Environment ◽  
Interfacial Water ◽  
Functional Theory ◽  
Oxidation Mechanisms ◽  
Insight Into

In this work, we have studied methanol oxidation mechanisms on RuO2(100) by using density functional theory (DFT) calculations and ab initio molecular dynamics (MD) simulations with some explicit interfacial water molecules.

Mechanistic Study of the Cooperative Palladium/Lewis Acid-Catalyzed Transfer Hydrocyanation Reaction: The Origin of the Regioselectivity

2021 ◽  
Author(s):  
Dandan Jiang ◽  
Xiaojun Li ◽  
Jiali Cai ◽  
Yuna Bai ◽  
Lixiong Zhang ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Dft Calculations ◽  
Lewis Acid ◽  
Density Functional ◽  
Catalytic Mechanism ◽  
Mechanistic Study ◽  
Functional Theory ◽  
Terminal Alkenes ◽  
Acid Catalyzed ◽  
Insight Into

Density functional theory (DFT) calculations have been performed to gain insight into the catalytic mechanism of the Palladium/Lewis acid-catalyzed transfer hydrocyanation of terminal alkenes to reach the linear alkyl nitrile...

Mechanisms for the formation of epoxide and chlorine-containing products in the oxidation of ethylene by chromyl chloride: a density functional study

1999 ◽  
Vol 77 (9) ◽  
pp. 1476-1491 ◽  
Author(s):  
Maricel Torrent ◽  
Liqun Deng ◽  
Miquel Duran ◽  
Miquel Solà ◽  
Tom Ziegler
Keyword(s):  
Density Functional Theory ◽  
Reaction Mechanisms ◽  
Density Functional ◽  
Activation Barrier ◽  
Activation Energies ◽  
Functional Study ◽  
Functional Theory ◽  
Activation Barriers ◽  
Density Functional Study ◽  
Chromyl Chloride

The reaction between CrO2Cl2 and ethylene leading to the formation of epoxide and chlorohydrin precursors or directly to 1,2-dichloroethane has been studied by density functional theory. The formation of the epoxide precursor (Cl2(O)Cr-OC2H4) was found to take place via a [3+2] addition of ethylene to two Cr=O bonds followed by rearrangement of the five-membered diol to the epoxide product. The alternative mechanisms involving a direct addition of oxygen to ethylene or the [2+2] addition of the olefin to a Cr=O bond were found to have much higher activation energies. The formation of the chlorohydrin precursor (Cl(O)Cr-OCH2=CHCl) was found to take place via a [3+2] addition to one Cr—Cl and one Cr=O bond. Pathways involving initial [2+2] addition to a Cr—Cl or Cr=O bond had much higher activation barriers. The generation of 1,2-dichloroethane is highly unfavorable with an endothermicity of 44.7 kcal/mol and an even higher activation barrier. It is suggested that the formation of epoxide and chlorohydrin from the respective precursors requires the addition of H2O.Key words: reaction mechanisms, epoxide, oxidation of ethylene, chromyl chloride, DFT.

scholarly journals Machine learning enabling prediction of the bond dissociation enthalpy of hypervalent iodine from SMILES

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Masaya Nakajima ◽  
Tetsuhiro Nemoto
Keyword(s):  
Machine Learning ◽  
Dft Calculations ◽  
Density Functional ◽  
High Accuracy ◽  
Machine Learning Algorithms ◽  
Hypervalent Iodine ◽  
Bond Dissociation Enthalpy ◽  
Important Indicator ◽  
Bond Dissociation ◽  
Dissociation Enthalpy

AbstractMachine learning to create models on the basis of big data enables predictions from new input data. Many tasks formerly performed by humans can now be achieved by machine learning algorithms in various fields, including scientific areas. Hypervalent iodine compounds (HVIs) have long been applied as useful reactive molecules. The bond dissociation enthalpy (BDE) value is an important indicator of reactivity and stability. Experimentally measuring the BDE value of HVIs is difficult, however, and the value has been estimated by quantum calculations, especially density functional theory (DFT) calculations. Although DFT calculations can access the BDE value with high accuracy, the process is highly time-consuming. Thus, we aimed to reduce the time for predicting the BDE by applying machine learning. We calculated the BDE of more than 1000 HVIs using DFT calculations, and performed machine learning. Converting SMILES strings to Avalon fingerprints and learning using a traditional Elastic Net made it possible to predict the BDE value with high accuracy. Furthermore, an applicability domain search revealed that the learning model could accurately predict the BDE even for uncovered inputs that were not completely included in the training data.

Sign in / Sign up

Export Citation Format

Share Document