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.

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.

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

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.

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