scholarly journals Metal Enolates – Enamines – Enol Ethers: How Do Enolate Equivalents Differ in Nucleophilic Reactivity?

Synthesis ◽  
2019 ◽  
Vol 51 (05) ◽  
pp. 1157-1170 ◽  
Author(s):  
Artem Leonov ◽  
Daria Timofeeva ◽  
Armin Ofial ◽  
Herbert Mayr
Keyword(s):  
Rate Constants ◽  
Correlation Equation ◽  
Stopped Flow ◽  
Quinone Methides ◽  
Enol Ethers ◽  
Reactivity Descriptors ◽  
Silyl Enol Ethers ◽  
Nucleophilic Reactivity ◽  
Kinetics Of ◽  
Least Squares Minimization

The kinetics of the reactions of trimethylsilyl enol ethers and enamines (derived from deoxybenzoin, indane-1-one, and α-tetralone) with reference electrophiles (p-quinone methides, benzhydrylium and indolylbenzylium ions) were measured by conventional and stopped-flow photometry in acetonitrile at 20 °C. The resulting second-order rate constants were subjected to a least-squares minimization based on the correlation equation lg k = s N(N + E) for determining the reactivity descriptors N and s N of the silyl enol ethers and enamines. The relative reactivities of structurally analogous silyl enol ethers, enamines, and enolate anions towards carbon-centered electrophiles are determined as 1, 107, and 1014, respectively. A survey of synthetic applications of enolate ions and their synthetic equivalents shows that their behavior can be properly described by their nucleophilicity parameters, which therefore can be used for designing novel synthetic transformations.

Comparison of the nucleophilicities of alcohols and alkoxides

2005 ◽  
Vol 83 (9) ◽  
pp. 1554-1560 ◽  
Author(s):  
Thanh Binh Phan ◽  
Herbert Mayr
Keyword(s):  
Free Energy ◽  
Key Words ◽  
Rate Constants ◽  
Correlation Equation ◽  
Linear Free Energy Relationship ◽  
Hydroxide Solution ◽  
Linear Free Energy ◽  
S Parameters ◽  
Nucleophilic Reactivity ◽  
Kinetics Of

The kinetics of the reactions of benzhydrylium ions with some alcohols and alkoxides dissolved in the corresponding alcohols were photometrically investigated. Using the correlation equation log k (20 °C) = s(E + N), the N and s parameters of methoxide, ethoxide, n-propoxide, and isopropoxide in alcohol–acetonitrile (91:9, v/v) were determined. The cosolvent acetonitrile has only a little influence on the rate constants of the reactions of alcohols and alkoxides. The order of N values (OH– << MeO– < EtO– < n-PrO– < i-PrO–) shows that alkoxides differ only moderately in reactivity but are considerably more nucleophilic than hydroxide. As a consequence, the nucleophilic reactivity of a 0.5 mmol/L aqueous hydroxide solution increases by a factor of 13 when 10% (v/v) methanol is added. In 1–10 mmol/L alkoxide solutions in alcohols, weak electrophiles react considerably faster with alkoxides than with the corresponding alcohols. With increasing electrophilicity, the preference for alkoxides decreases, and electrophiles of –3 < E < 3 react with alkoxides (1–10 mmol/L) and alcohols with comparable rates. Stronger electrophiles will react with alcohols exclusively when alkoxides are present in concentrations ≤10 mmol/L. Key words: kinetics, alcohol, alkoxide, linear free energy relationship, nucleophilicity.<

Kinetics of electrophile-nucleophile combinations: A general approach to polar organic reactivity

2005 ◽  
Vol 77 (11) ◽  
pp. 1807-1821 ◽  
Author(s):  
Herbert Mayr ◽  
Armin R. Ofial
Keyword(s):  
Transition Metal ◽  
Correlation Equation ◽  
Organic Reactions ◽  
Diazo Compounds ◽  
Quinone Methides ◽  
Enol Ethers ◽  
Different Types ◽  
Michael Acceptors ◽  
Kinetics Of ◽  
Organic Reactivity

Benzhydrylium ions (Ar2CH+) and structurally related quinone methides are employed as reference electrophiles for comparing the nucleophilicities of a large variety of compounds, e.g., alkenes, arenes, alkynes, allylsilanes, allylstannanes, enol ethers, enamines, diazo compounds, carbanions, transition-metal π-complexes, hydride donors, phosphanes, amines, alkoxides, etc., using the correlation equation log k (20 °C) = s(N + E), where s and N are nucleophile-dependent parameters and E is an electrophilicity parameter. The same equation was employed to derive the electrophilicity parameter E for different types of carbocations, cationic transition-metal π-complexes, typical Michael acceptors, and electron-deficient arenes. The E, N, and s parameters thus obtained can be used for predicting rates and selectivities of polar organic reactions.

scholarly journals The Kinetics of Peroxynitrite on Insulin Nitration Damage

2020 ◽  
Author(s):  
Congxiao Zhang ◽  
Fusheng Sun ◽  
Congjiang Zhang ◽  
Yunjing Luo
Keyword(s):  
Activation Energy ◽  
Biological Activity ◽  
Glucose Metabolism ◽  
Rate Constants ◽  
The Body ◽  
Stopped Flow ◽  
Tyrosine Nitration ◽  
Protein Nitration ◽  
Physiological Conditions ◽  
Kinetics Of

Abstract Background: Insulin is one of the most important versatile hormones that is central to regulating the energy and glucose metabolism in the body. There has been accumulating evidence supporting that diabetes was associated with peroxynitrite and protein nitration, and insulin nitration induced by peroxynitrite affected its biological activity. Methods: In this paper, the kinetics of insulin nitration by peroxynitrite in physiological conditions was studied by the stopped flow technique. Results: We determined the values of the reactive rate constants of peroxynitrite decomposition and peroxynitrite-induced tyrosine nitration in the presence of insulin. The activation energy of peroxynitrite decomposition and 3-nitrotyrosine yield in the presence of insulin is 48.8 kJ·mol−1 and 42.7 kJ·mol−1 respectively. Conclusions: It is inferred that the glutamate residue of insulin accelerated peroxynitrite decomposition and tyrosine nitration by reducing the activation energy of reactions. The results could be beneficial for exploring the molecular mechanism of diabetes and offering a new target for diabetes therapies.

Kinetik der Reaktion von 2.4-Dinitrofluorbenzol mit Imidazol-, SH- und Imidazol-SH-Verbindungen / Kinetics of the Reaction of 2,4-dinitro-1-fluorobenzene with Imidazole-, SH- and Imidazole-SH-compounds

1971 ◽  
Vol 26 (10) ◽  
pp. 1010-1016 ◽  
Author(s):  
Renate Voigt ◽  
Helmut Wenck ◽  
Friedhelm Schneider
Keyword(s):  
Temperature Dependence ◽  
Rate Constants ◽  
Reaction Rate ◽  
Ph Dependence ◽  
First Order ◽  
Molecular Transfer ◽  
Thiolate Anion ◽  
Nucleophilic Reactivity ◽  
Kinetics Of ◽  
Lindley Equation

First order rate constants of the reaction of a series of SH-, imidazole- and imidazole/SH-compounds with FDNB as well as their pH- and temperature dependence were determined. Some of the tested imidazole/SH-compounds exhibit a higher nucleophilic reactivity as is expected on the basis of their pKSH-values. This enhanced reactivity is caused by an activation of the SH-groups by a neighbouring imidazole residue. The pH-independent rate constants were calculated using the Lindley equation.The kinetics of DNP-transfer from DNP-imidazole to SH-compounds were investigated. The pH-dependence of the reaction displays a maximum curve. Donor in this reaction is the DNP-imidazolecation and acceptor the thiolate anion.The reaction rate of FDNB with imidazole derivatives is two to three orders of magnitude slower than with SH-compounds.No inter- or intra-molecular transfer of the DNP-residue from sulfure to imidazole takes place.

Mechanism of bromination of a quaternary pyrimidinium cation. Change of rate determining step with acidity

1978 ◽  
Vol 56 (23) ◽  
pp. 2970-2976 ◽  
Author(s):  
Oswald S. Tee ◽  
David C. Thackray ◽  
Charles G. Berks
Keyword(s):  
Kinetic Study ◽  
Rate Constants ◽  
Aqueous Media ◽  
Stopped Flow ◽  
Flow Method ◽  
High Acidity ◽  
Rate Determining Step ◽  
Kinetics Of ◽  
Good Agreement

The kinetics of bromination of the 1,2-dihydro-1,3-dimethyl-2-oxopyrimidinium cation (Q+) in aqueous media (pH 0–5) have been studied using the stopped-flow method. At the higher acidities (pH < 2) the results are consistent with rate determining attack by bromine upon the pseudobase (QOH), whereas at low acidities (pH > 4) it appears that pseudobase formation is rate determining. The change occurs because at high acidity the reversal of the pseudobase QOH to the cation is fast relative to bromine attack, whereas at low acidity the converse is true. Results obtained at intermediate acidities (pH 2–4) are consistent with this interpretation.A separate kinetic study of pseudobase formation (and decomposition) yielded rate constants in good agreement with those derived from the bromination study.

Kinetics of reactions of para-substituted phenyl isocyanates with amines and alcohols

1991 ◽  
Vol 56 (8) ◽  
pp. 1662-1670 ◽  
Author(s):  
Ivan Danihel ◽  
Falk Barnikol ◽  
Pavol Kristian
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Rate Constants ◽  
Substituent Effects ◽  
Steric Effects ◽  
Stopped Flow ◽  
Partial Charges ◽  
Hammett Correlation ◽  
One Step ◽  
Kinetics Of

The reaction of para-substituted phenyl isocyanates with amines and alcohols was studied by stopped-flow method. The Hammett correlation obtained showed that the sensitivity of the above mentioned reactions toward substituent effects is the same as that of analogous reactions of phenyl isothiocyanates (ρ ~ 2). The rate constants of these reactions were found to be affected more by steric effects than by solvent effects. An one step multicentre mechanism with partial charges in transition state has been proposed for the title reactions.

Kinetics of oxidation of thiocyanate by aqueous iodine

1973 ◽  
Vol 26 (9) ◽  
pp. 1863 ◽  
Author(s):  
GT Briot ◽  
RH Smith
Keyword(s):  
Rate Constants ◽  
Activation Energies ◽  
Stopped Flow ◽  
Kinetics Of Oxidation ◽  
Rate Law ◽  
General Base ◽  
Present Rate ◽  
Rapid Equilibrium ◽  
Ph Range ◽  
Kinetics Of

The kinetics of oxidation of thiocyanate to sulphate by aqueous iodine in the pH range 9.2-12.5 have been studied using a spectrophotometric stopped flow technique. The reaction is general base-catalysed, having the rate law ��������������������� -d[I2]a/dt = ([SCN-][I3-]/[I-]2)Σ kB[B] where [I2]a is the total analytical concentration of iodine, [B] is the concentration of base, and where the summation is taken over all bases present. Rate constants, kB, and activation energies have been measured for the bases, OH-, PO43- and CO32-. ��� A mechanism involving the initial steps ����������������� I2+SCN- ↔ ISCN+I- �����������������(rapid equilibrium) ������������� ISCN+H2O+B → HOSCN+I- + HB+ �����������(rate determining) followed by rapid reactions of HOSCN with itself or with iodine is proposed.

Reactivity of nucleophiles in dimethyl sulfoxide and its comparison with nucleophilic reactivity in protic medium

1989 ◽  
Vol 54 (10) ◽  
pp. 2715-2720 ◽  
Author(s):  
Vítězslav Zima ◽  
Oldřich Pytela ◽  
Jaromír Kaválek ◽  
Miroslav Večeřa
Keyword(s):  
Dimethyl Sulfoxide ◽  
Electrostatic Interaction ◽  
Rate Constants ◽  
Reaction Medium ◽  
Correlation Equation ◽  
Regression Coefficients ◽  
Aprotic Solvents ◽  
Protic Solvents ◽  
Nucleophilic Reactivity

Reactions of 2,4-dinitrophenyl acetate and 2,4-dinitrofluorobenzene as model substrates with 12 nucleophiles have been studied in dimethyl sulfoxide. The rate constants obtained have been discussed with regard to the nucleophilic reactivity differences in dimethyl sulfoxide and protic solvents inclusive of the different manifestation of the charge of nucleophiles. The applicability of an earlier-suggested correlation equation to the data obtained has been verified. The reaction medium markedly affects the reactivity of nucleophiles, the effect of charge being substantially greater in aprotic solvents (electrostatic interaction) than in protic ones (solvation). In spite of these differences the correlation with application of an empirical nucleophilicity scale suggested earlier is satisfactory, the regression coefficients obtained reflect changes in the nature of medium.

scholarly journals Reaction Kinetics of Carbon Dioxide in Aqueous Diethanolamine Solutions Using the Stopped-Flow Technique

2012 ◽  
Vol 19 (1) ◽  
pp. 55-66 ◽  
Author(s):  
Marta Siemieniec ◽  
Hanna Kierzkowska-Pawlak ◽  
Andrzej Chacuk
Keyword(s):  
Carbon Dioxide ◽  
Reaction Kinetics ◽  
Rate Constants ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
Stopped Flow ◽  
First Order ◽  
Pseudo First Order ◽  
Kinetics Of ◽  
Good Agreement

Reaction Kinetics of Carbon Dioxide in Aqueous Diethanolamine Solutions Using the Stopped-Flow Technique The pseudo-first-order rate constants (kOV) for the reactions between CO2 and diethanolamine have been studied using the stopped-flow technique in an aqueous solution at 293, 298, 303 and 313 K. The amine concentrations ranged from 167 to 500 mol·m-3. The overall reaction rate constant was found to increase with amine concentration and temperature. Both the zwitterion and termolecular mechanisms were applied to correlate the experimentally obtained rate constants. The values of SSE quality index showed a good agreement between the experimental data and the corresponding fit by the use of both mechanisms.

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