Structure reactivity relationship in the accelerated formation of 2,3-diarylquinoxalines in the microdroplets of a nebuliser

2019 ◽  
Vol 25 (6) ◽  
pp. 457-462
Author(s):  
Nadia Hayat ◽  
Nathan W Fenwick ◽  
Amie Saidykhan ◽  
Richard Telford ◽  
William HC Martin ◽  
...  
Keyword(s):  
Carbonyl Group ◽  
Nucleophilic Addition ◽  
Negative Charge ◽  
Appreciable Amount ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Structure Reactivity Relationship ◽  
Rate Limiting ◽  
Hammett Relationship

Competition experiments in which 1,2-phenylenediamine, C6H4(NH2)2, condenses with equimolar quantities of benzil, (C6H5CO)2, and a 3,3′- or 4,4′-disubstituted benzil (XC6H4CO)2 (X = F, Cl, Br, CH3 or CH3O) to form a mixture of 2,3-diphenylquinoxaline and the corresponding 2,3-diarylquinoxaline (Ar = XC6H4) in the microdroplets produced in a nebuliser allow a Hammett relationship with a ρ value of 1.85 to be developed for this accelerated condensation in the nebuliser. This structure reactivity relationship reveals that an appreciable amount of negative charge builds up on the carbon of the carbonyl group of the benzil during the rate-limiting step of the reaction, thus confirming that this process involves nucleophilic addition of the 1,2-phenylenediamine to the benzil. In general, the presence of an electron donating substituent, particularly in the 4 and 4′ positions, in the benzil retards the reaction, whereas an electron attracting substituent, especially in the 3 and 3′ position, accelerates it.

Reactions of 1,3-diacylthioureas with methoxide ion and with amines

1987 ◽  
Vol 52 (1) ◽  
pp. 120-131 ◽  
Author(s):  
Jaromír Kaválek ◽  
Josef Jirman ◽  
Vojeslav Štěrba
Keyword(s):  
Carbonyl Group ◽  
Rate Constants ◽  
Dissociation Constants ◽  
Equilibrium Constants ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Order Of Magnitude ◽  
Acetyl Group ◽  
Methoxide Ion ◽  
Rate Limiting

Rate constants of base-catalyzed methanolysis and dissociation constants in methanol have been determined for benzoylthiourea (II), 1,3-diacetylthiourea (III), 1,3-dibenzoylthiourea (IV), and 1-acetyl-3-benzoylthiourea (V). With the diacyl derivatives III and IV, the reaction of methoxide ion with the neutral substrate is accompanied by that of methoxide with the substrate anion (at higher alkoxide concentrations). Above 0.1 mol l-1 CH3O(-), the rate constants are also affected by medium. The rate of the reaction of neutral diacyl derivative is decreased, and that of the reaction of methoxide with the substrate anion is rapidly increased. The dissociation constant of II is higher than that of acetylthiourea (I) by about one order of magnitude, but the attack of methoxide on the carbonyl group of II is about three times slower than that in I. The benzoyl group at the N1 nitrogen exhibits a greater activating influence (in both the rate and the equilibrium constants) on the other NHCOR group than the acetyl group does. With V the ratio of methanolysis rate constants is 9 : 1 in favour of the acetyl group. The reaction of diacetyl derivative III with 1-butanamine has been followed in butanamine buffers. At the lowest butanamine concentrations, the reaction is second order in the amine, and the rate-limiting step is the proton transfer from the intermediate to the second amine molecule. At the highest butanamine concentrations the reaction becomes first order in the amine, and the rate-limiting step changes to the attack of butanamine on the carbonyl group of diacetyl derivative III.

Notizen: Mechanistic Implication of “LFER” in the Oxidation of Acetophenones by Vanadium(V)

1976 ◽  
Vol 31 (1) ◽  
pp. 140-141 ◽  
Author(s):  
M. S. Kelkar ◽  
R. Shanker ◽  
G. V. Baxore
Keyword(s):  
Linear Combination ◽  
Effect Of Substituents ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Structure Reactivity Relationship ◽  
Relationship Of ◽  
Rate Limiting

A linear combination of the effect of substituents on pre-equilibrium and subsequent rate limiting step, K and k respectively, describes the structure reactivity, relationship of the form log k/k0 = -2.17σ++ 3.3 σ, where former corresponds to V(V)-ketone complex and the latter its rate limiting disproportionation

Stereochemistry and kinetics of amines addition to acetylenic esters

1991 ◽  
Vol 69 (9) ◽  
pp. 1445-1449 ◽  
Author(s):  
Saber M. Sharaf ◽  
Samir K. El-Sadany ◽  
Ezzat A. Hamed ◽  
Abdel-Hamid A. Youssef
Keyword(s):  
Key Words ◽  
Nucleophilic Addition ◽  
Nmr Spectra ◽  
Acetylenic Esters ◽  
H Nmr ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Step Mechanism

The reactions of a series of methyl para-substituted phenylpropiolates 1a–e with piperidine, morpholine, and diethylamine in methanol and dimethylformamide (DMF) have been studied and their rates measured. The products were methyl β-(N,N-dialkylamino)-p-substituted cinnamates 2–4a–e. 1H NMR spectra were used to determine the configuration of the products. The ρ values in methanol ranged between 0.34 and 1.24 whereas in DMF they were between 0.85 and 1.88. The values of ΔS≠ favor a bimolecular rate-limiting step mechanism. Key words: nucleophilic addition to acetylenic esters.

scholarly journals Hammett Correlation in the Accelerated Formation of 2,3-Diphenylquinoxalines in Nebulizer Microdroplets

Molecules ◽  
2021 ◽  
Vol 26 (16) ◽  
pp. 5077
Author(s):  
Nathan W. Fenwick ◽  
Richard Telford ◽  
Amie Saidykhan ◽  
William H. C. Martin ◽  
Richard D. Bowen
Keyword(s):  
Electron Density ◽  
Aromatic Ring ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Hammett Correlation ◽  
Structure Reactivity Relationship ◽  
Rate Limiting

The accelerated formation of 2,3-diphenylquinoxalines in microdroplets generated in a nebulizer has been investigated by competition experiments in which equimolar quantities of 1,2-phenylenediamine, C6H4(NH2)2, and a 4-substituted homologue, XC6H3(NH2)2 [X = F, Cl, Br, CH3, CH3O, CO2CH3, CF3, CN or NO2], or a 4,5-disubstituted homologue, X2C6H2(NH2)2 [X = F, Cl, Br, or CH3], compete to condense with benzil, (C6H5CO)2. Electron-donating substituents (X = CH3 and CH3O) accelerate the reaction; in contrast, electron-attracting substituents (X = F, Cl, Br and particularly CO2CH3, CN, CF3 and NO2) retard it. A structure–reactivity relationship in the form of a Hammett correlation has been found by analyzing the ratio of 2,3-diphenylquinoxaline and the corresponding substituted-2,3-diphenylquinoxaline, giving a ρ value of −0.96, thus confirming that the electron density in the aromatic ring of the phenylenediamine component is reduced in the rate-limiting step in this accelerated condensation. This correlation shows that the phenylenediamine acts as a nucleophile in the reaction.

Cluster Model Theoretical Study of the Interaction and Penetration of F on a Si Surface

1984 ◽  
Vol 38 ◽  
Author(s):  
Paul S. Bagus
Keyword(s):  
Binding Energy ◽  
Ionization Potential ◽  
Electron Affinity ◽  
Cluster Model ◽  
Theoretical Study ◽  
Negative Charge ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Proper Account

AbstractThe interaction of fluorine with a three-fold open site of the Si(111) surface has been examined using a cluster model. The site considered is taken as representative of one where penetration of the surface may occur. New analyses are used to show that the interaction is ionic with F having essentially a full negative charge for all distances near the surface, both above and below. The bonding is shown to be almost entirely electrostatic between the polarized charges of the positive Si surface and F-. The F-Si binding energy is estimated taking proper account of the electron affinity of F and the ionization potential, work function, of Si. When this is done, it is shown that there is no barrier for the penetration of the Si surface by F; hence, this penetration should not be a rate limiting step in the F-Si etching reaction.

Ornithine Decarboxylase Activity in Cultured Endothelial Cells Stimulated by Serum, Thrombin and Serotonin

1978 ◽  
Vol 39 (02) ◽  
pp. 496-503 ◽  
Author(s):  
P A D’Amore ◽  
H B Hechtman ◽  
D Shepro
Keyword(s):  
Endothelial Cells ◽  
Ornithine Decarboxylase ◽  
Decarboxylase Activity ◽  
Aortic Endothelial Cells ◽  
Ornithine Decarboxylase Activity ◽  
Rate Limiting Step ◽  
Bovine Aortic Endothelial Cells ◽  
Limiting Step ◽  
Rate Limiting ◽  
Serum Serotonin

SummaryOrnithine decarboxylase (ODC) activity, the rate-limiting step in the synthesis of polyamines, can be demonstrated in cultured, bovine, aortic endothelial cells (EC). Serum, serotonin and thrombin produce a rise in ODC activity. The serotonin-induced ODC activity is significantly blocked by imipramine (10-5 M) or Lilly 11 0140 (10-6M). Preincubation of EC with these blockers together almost completely depresses the 5-HT-stimulated ODC activity. These observations suggest a manner by which platelets may maintain EC structural and metabolic soundness.

Dynamics of hepatic and peripheral insulin effects suggest common rate-limiting step in vivo

Diabetes ◽  
1993 ◽  
Vol 42 (2) ◽  
pp. 296-306 ◽  
Author(s):  
D. C. Bradley ◽  
R. A. Poulin ◽  
R. N. Bergman
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting
Sign in / Sign up

Export Citation Format

Share Document