scholarly journals DFT study on the mechanism of simultaneous trifluoromethylation and oximation of aryl-substituted ethylene.

2021 ◽  
Author(s):  
Sen Wang ◽  
Ao He ◽  
Xuan Meng ◽  
Xiao wei Lan ◽  
Xianfu Wei ◽  
...  
Keyword(s):  
Carbon Atom ◽  
Proton Transfer ◽  
Organic Solvent ◽  
Solvent Effect ◽  
Aromatic Ring ◽  
Organic Solvents ◽  
Energy Barrier ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

The effects of different substituents located at the para position of the aromatic ring and β carbon atom of the styrene on the reaction were investigated. The results showed that the reaction steps with higher energy barriers changed a little with the substituents of the reactants, which indicates that the reaction has a good adaptability to reactants containing different substituents. It was found the proton transfer in the final tautomerism step of nitroso intermediate to oxime is the rate limiting step under anhydrous conditions. Although the solvent effect did not influence the the rate limiting step significantly, the water mediated proton transfer significantly decreased the energy barrier of final tautomerism step. Compared with the direct proton transfer in vacuum, the energy barrier of the final tautomerism step decreased from 57.80kcal/mol in vacuum to 12.98kcal/mol with the water mediated proton transfer in water, which declined by 77.5%. When water participates in rate-limiting steps in organic solvents, the energy barrier also decreases significantly, which indicates that a small amount of water in the organic solvent is conducive to the reaction. This study is of great significance for the application of bifunctionalized reaction in the synthesis of organic fluoride compounds with different substituents.

scholarly journals Atomically manipulated proton transfer energizes water oxidation on silicon carbide photoanodes

2018 ◽  
Vol 6 (47) ◽  
pp. 24358-24366 ◽  
Author(s):  
Hao Li ◽  
Huan Shang ◽  
Yuchen Shi ◽  
Rositsa Yakimova ◽  
Mikael Syväjärvi ◽  
...  
Keyword(s):  
Silicon Carbide ◽  
Electron Transfer ◽  
Proton Transfer ◽  
Water Oxidation ◽  
Proton Coupled Electron Transfer ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Preferential exposure of Si-face of SiC will mechanistically shift the rate limiting step of water oxidation from sluggish proton-coupled electron transfer on C-face to a more energy-favorable electron transfer.

Oxidation of 1- and 2-acetylnaphthalenes by iodate - a kinetic study

1990 ◽  
Vol 55 (6) ◽  
pp. 1535-1540 ◽  
Author(s):  
Prerepa Manikyamba
Keyword(s):  
Solvent Effect ◽  
Enol Form ◽  
Aqueous Methanol ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
Carbonium Ion ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of oxidation of 1- and 2-acetylnaphthalenes by iodate in the presence of sulphuric acid in aqueous methanol has been studied. The reaction is first order with respect to both [iodate] and [acetylnaphthalene]. Solvent effect indicates a cation-dipole type of interaction in the rate limiting step. A mechanism is proposed with a slow attack of IO2+ on enol form of acetylnaphthalene forming an intermediate carbonium ion, which ultimately gives corresponding ω-hydroxyacetylnaphthalene. The higher reactivity of 2-acetyl isomer is attributed to the greater stability of the corresponding carbonium ion than that of 1-acetyl isomer.

A mathematical modelling of acid catalyzed decomposition of 3-methyl-1,3-diphenyltriazene

1987 ◽  
Vol 52 (10) ◽  
pp. 2492-2499 ◽  
Author(s):  
Oldřich Pytela ◽  
Petr Svoboda ◽  
Miroslav Večeřa
Keyword(s):  
Reaction Mechanism ◽  
Linear Regression ◽  
Organic Solvent ◽  
Mathematical Modelling ◽  
Aqueous Ethanol ◽  
Activation Parameters ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Acid Catalyzed ◽  
Rate Limiting

The effect of acids on the decomposition of 3-methyl-1,3-diphenyltriazene has been studied in aqueous ethanol (40% (v/v) ethanol). The dependences found between the rate constant and acid concentration have been analyzed by means of non-linear regression using models including the specific and general catalysis and formation of associates between the substrate and the buffer components. The substrate has been found to form electrostatic associates with the conjugated base of acid. The complex formed is decomposed with the assistance of the proton or a general acid in the rate-limiting step to form the product. The Bronsted coefficient α = 0.81 has been found. Investigation of the activation parameters supports the earlier conclusions, indicating a dependence between the reaction mechanism and composition of the aqueous organic solvent.

Base-catalyzed formation of spiro adduct from N-methyl-N-(2,4,6-trinitrophenyl)glycinamide, the smiles rearrangement of the amide in methanol

1988 ◽  
Vol 53 (3) ◽  
pp. 601-618 ◽  
Author(s):  
Jaromír Kaválek ◽  
Vladimír Macháček ◽  
Makky M. M. Hassanien ◽  
Vojeslav Štěrba
Keyword(s):  
Proton Transfer ◽  
Equilibrium Constant ◽  
Ammonium Salt ◽  
Aliphatic Amine ◽  
Reaction Pathway ◽  
Smiles Rearrangement ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Kinetics Of

The reaction of N-methyl-N-(2,4,6-trinitrophenyl)glycinamide (Ic with methoxide in methanol produces the spiro adduct IIc(A). In methanolic acetate buffers, the equilibrium is rapidly established between the spiro adduct IIc(A) and the dipolar ion of 2-methylamino-N-(2,4,6-trinitrophenyl)acetamide (IIIc(Z)). The equilibrium constant of the reaction IIIc(Z) ⇆ IIc(A) + H+ is by eight orders of magnitude greater than that of the analogous cyclization of 2-methylamino-N-methyl-N-(2,4,6-trinitrophenyl)acetamide to the spiro adduct. In chloracetate buffers, the dipolar ion is protonated to give 2-methylammonium-N-(2,4,6-trinitrohenyl)acetamide IIIc(K). The kinetics of the reversible reaction IIIc(Z) ⇆ IIc(A) + H+ has been studied in acetate buffers, aliphatic amine – ammonium salt buffers, and methoxide solutions. In all cases, the rate-limiting step was the proton transfer with half-lives in milliseconds. In more basic methanolic buffers (pH > 10) the rate-limiting step consists in the formation of spiro adduct from the zwiterion IIIc(Z) resulting from the protonation of the anion IIIc(A). n acetate buffers, the second reaction pathway via the cation IIIc(K) is predominant.

Ketimine-enamine tautomerism of 2-ethoxycarbonylmethylene-4-methyl-3-oxo-1,2,3,4-tetrahydroquinoxaline: A kinetic study

1981 ◽  
Vol 46 (9) ◽  
pp. 2104-2109
Author(s):  
Jaromír Toman ◽  
Vojeslav Štěrba ◽  
Jiří Klicnar
Keyword(s):  
Carbon Atom ◽  
Solvent Effects ◽  
Title Compound ◽  
Base Catalysis ◽  
Methine Carbon ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Acid And Base ◽  
Acid Catalyzed ◽  
Rate Limiting

Tautomerism of the title compound in methanol in the presence of buffers is subject to general acid and base catalysis. The rate-limiting step of the acid-catalyzed reaction consists in addition of the proton to the methine carbon atom of the enamine form, whereas that of the base catalyzed reaction consists in protonation of the formed conjugated base of the enamine. Solvent effects on the equilibrium constant of the isomerization have been measured.

THEORETICAL STUDY ON CUI-CATALYZED LIGAND-FREE N-ARYLATION OF IMIDAZOLE WITH BROMOBENZENE

2012 ◽  
Vol 11 (05) ◽  
pp. 1135-1147 ◽  
Author(s):  
HAN GUO ◽  
YING XUE
Keyword(s):  
Free Energy ◽  
Energy Barrier ◽  
Density Functional ◽  
Oxidative Addition ◽  
Reductive Elimination ◽  
Free Energy Barrier ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Ligand Free ◽  
Rate Limiting

The density functional theory (DFT) is used to investigate the mechanism of ligand-free CuI -catalyzed N -arylation of imidazole with aryl halide. The oxidative addition/reductive elimination mechanism is adopted via two different pathways to form the same Cu(III) intermediate. Comparing two pathways, the path 1 in which the imidazolyl coordination occurs prior to the oxidative addition is more favorable, because the free energy barrier of the rate-limiting step of path 1 is lower than the barrier of the other. In addition, it leads to a relative stable intermediate which can promote the reaction to process via path 1. And the overall free energy barrier of oxidative addition to imidazole-ligated Cu(I) complex is not high enough when comparing with the diamine-promote process, which can further prove that the N -arylation of imidazole is feasible in the absence of additional ligands. Nucleophile coordination and reductive elimination steps are facile, while the oxidative addition is the rate-limiting step.

A novel single-atom catalyst for CO oxidation in humid environmental conditions: Ni-embedded divacancy graphene

2020 ◽  
Vol 8 (1) ◽  
pp. 287-295 ◽  
Author(s):  
Quanguo Jiang ◽  
Jianfeng Zhang ◽  
Huajie Huang ◽  
Yuping Wu ◽  
Zhimin Ao
Keyword(s):  
Co Oxidation ◽  
Environmental Conditions ◽  
Energy Barrier ◽  
Single Atom ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

A termolecular Eley–Rideal (TER) mechanism is preferred for CO oxidation on Ni-DG in humid environments, and the energy barrier for the rate limiting step (2CO + O2 → OCOOCO) is only 0.34 eV.

scholarly journals Substrate-Dependent Sensitivity of SIRT1 to Nicotinamide Inhibition

Biomolecules ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 312
Author(s):  
Stacia Rymarchyk ◽  
Wenjia Kang ◽  
Yana Cen
Keyword(s):  
Proton Transfer ◽  
Isotope Effects ◽  
Negative Regulator ◽  
Base Exchange ◽  
Glucose And Lipid Metabolism ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Catalyzed Reactions ◽  
Solvent Isotope ◽  
Rate Limiting

SIRT1 is the most extensively studied human sirtuin with a broad spectrum of endogenous targets. It has been implicated in the regulation of a myriad of cellular events, such as gene transcription, mitochondria biogenesis, insulin secretion as well as glucose and lipid metabolism. From a mechanistic perspective, nicotinamide (NAM), a byproduct of a sirtuin-catalyzed reaction, reverses a reaction intermediate to regenerate NAD+ through “base exchange”, leading to the inhibition of the forward deacetylation. NAM has been suggested as a universal sirtuin negative regulator. Sirtuins have evolved different strategies in response to NAM regulation. Here, we report the detailed kinetic analysis of SIRT1-catalyzed reactions using endogenous substrate-based synthetic peptides. A novel substrate-dependent sensitivity of SIRT1 to NAM inhibition was observed. Additionally, SIRT1 demonstrated pH-dependent deacetylation with normal solvent isotope effects (SIEs), consistent with proton transfer in the rate-limiting step. Base exchange, in contrast, was insensitive to pH changes with no apparent SIEs, indicative of lack of proton transfer in the rate-limiting step. Consequently, NAM inhibition was attenuated at a high pH in proteated buffers. Our study provides new evidence for “activation by de-repression” as an effective sirtuin activation strategy.

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