THE ALKALINE CLEAVAGE OF o-NITROBENZYLTRIMETHYLSILANE SOLVENT EFFECTS IN THE DIOXANE–WATER SYSTEM

1963 ◽  
Vol 41 (6) ◽  
pp. 1525-1530 ◽  
Author(s):  
H. R. Allcock
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Water System ◽  
Solvent Polarity ◽  
High Water ◽  
Aqueous Dioxane ◽  
Alkaline Cleavage ◽  
Rate Of Reaction ◽  
Kinetics Of

The kinetics of alkaline cleavage of o-nitrobenzyltrimethylsilane were examined in aqueous dioxane media. At high water concentrations, increases in solvent polarity retard the cleavage, as required by a mechanism involving charge dispersion in the transition state. At high dioxane concentrations, solvent polarity increases are accompanied by increases in the rate of reaction, a result which may reflect association between the solvent components.

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.

SOLVENT EFFECTS OF KINETICS OF [1,5] H-SHIFT IN CYCLOPENTADIENE AND ITS DERIVATIVES

2005 ◽  
Vol 04 (01) ◽  
pp. 151-161 ◽  
Author(s):  
VUDHICHAI PARASUK ◽  
SAKULSUK UNARUNOTAI
Keyword(s):  
Solvent Effects ◽  
Single Point ◽  
Solvent Polarity ◽  
Polarizable Continuum Model ◽  
Activation Energies ◽  
Free Energies ◽  
Solvent Systems ◽  
Polarizable Continuum ◽  
Kinetics Of ◽  
Fluoro Derivatives

Geometries of reactants, products (in the case of fluoro derivatives), and transition states in gas and solution phases of [1,5] H-shift of cyclopentadiene and 2-fluorocyclo-pentadiene were optimized using B3LYP/6-31++G(d,p) . The solvent effects were included using the Polarizable Continuum Model (PCM). Four solvent systems i.e. chloroform, dichloromethane, diethylether, and methanol, were considered. For cyclopentadiene, single point MP2/6-31++G(d,p) were also carried out. For cyclopentadiene and 2-fluorocyclopentadiene, using B3LYP/6-31++G(d,p) activation free energies of 25.47 and 28.74 kcal/mol respectively were yielded for the reaction in vacuum. In solutions, calculated activation energies for the reaction are slightly decreased with the reduction of around 0.5–3 kcal/mol depending on solvent. Good correlation between the solvent polarity and activation energies was also observed. Thus, the [1.5] H-shift in cyclopentadiene and its derivatives could be enhanced in polar solvents.

Solvent and temperature effects on the tautomerization of a carbonitrile molecule: A conductor-like polarizable continuum model (CPCM) study

2021 ◽  
Vol 20 (1) ◽  
pp. 59-68
Author(s):  
Zohreh Khanjari ◽  
Bita Mohtat ◽  
Reza Ghiasi ◽  
Hoorieh Djahaniani ◽  
Farahnaz Kargar Behbahani
Keyword(s):  
Gas Phase ◽  
Solvent Effects ◽  
Continuum Model ◽  
Solvent Polarity ◽  
Polarizable Continuum Model ◽  
Dielectric Constants ◽  
Frontier Orbitals ◽  
Reaction Field ◽  
Polarizable Continuum ◽  
Homo Lumo

This research examined the effects of solvent polarity and temperature on the tautomerization of a carbonitrile molecule at CAM-B3LYP/6-311G (d,p) level of theory. The selected solvents were n-hexane, diethyl ether, pyridine, ethanol, methanol, and water. The solvent effects were examined by the self-consistent reaction field theory (SCRF) based on conductor-like polarizable continuum model (CPCM). The solvent effects were explored on the energy barrier, frontier orbitals energies, and HOMO-LUMO gap. Dependencies of thermodynamic parameters (ΔG and ΔH) on the dielectric constants of solvents were also tested. Specifically, the temperature dependencies of the thermodynamics parameters were studied within 100–1000 K range. The rate constant of the tautomerism reaction was computed from 300 to 1200 K, in the gas phase.

On the Calculation of Transition State Activity Coefficient and Solvent Effects on Chemical Reactions

1998 ◽  
Vol 63 (12) ◽  
pp. 1969-1976 ◽  
Author(s):  
Alvaro Domínguez ◽  
Rafael Jimenez ◽  
Pilar López-Cornejo ◽  
Pilar Pérez ◽  
Francisco Sánchez
Keyword(s):  
Activity Coefficient ◽  
Transition State ◽  
Chemical Reactions ◽  
Solvent Effects ◽  
Transition State Theory ◽  
Reaction Medium ◽  
State Theory ◽  
Precursor Complex ◽  
State Activity ◽  
Classical Transition

Solvent effects, when the classical transition state theory (TST) holds, can be interpreted following the Brønsted equation. However, when calculating the activity coefficient of the transition state, γ# it is important to take into account that this coefficient is different from that of the precursor complex, γPC. The activity coefficient of the latter is, in fact, that calculated in classical treatments of salt and solvent effects. In this paper it is shown how the quotients γ#/γPC change when the reaction medium changes. Therefore, the conclusions taken on the basis of classical treatments may be erroneous.

Kinetics of lipase-catalyzed esterification in organic media: Correct model and solvent effects on parameters

1999 ◽  
Vol 24 (8-9) ◽  
pp. 463-470 ◽  
Author(s):  
Anja E.M. Janssen ◽  
Birte J. Sjursnes ◽  
Alexander V. Vakurov ◽  
Peter J. Halling
Keyword(s):  
Solvent Effects ◽  
Organic Media ◽  
Correct Model ◽  
Kinetics Of

scholarly journals Kinetics of thiamin cleavage by sulphite

1969 ◽  
Vol 113 (4) ◽  
pp. 611-615 ◽  
Author(s):  
J. Leichter ◽  
M. A. Joslyn
Keyword(s):  
Aqueous Solutions ◽  
Rate Constant ◽  
Sulphur Dioxide ◽  
First Order ◽  
Ph Values ◽  
Rate Of Reaction ◽  
Kinetics Of

Results are presented on the rate of thiamin cleavage by sulphite in aqueous solutions as affected by temperature (20–70°), pH(2·5–7·0), and variation of the concentration of either thiamin (1–20μm) or sulphite (10–5000μm as sulphur dioxide). Plots of the logarithm of percentage of residual thiamin against time were found to be linear and cleavage thus was first-order with respect to thiamin. At pH5 the rate was also found to be proportional to the sulphite concentration. In the pH region 2·5–7·0 at 25° the rate constant was 50m−1hr.−1 at pH5·5–6·0, and decreased at higher or lower pH values. The rate of reaction increased between 20° and 70°, indicating a heat of activation of 13·6kcal./mole.

The solvent effects on the kinetics of bacterial formate dehydrogenase reaction

1990 ◽  
Vol 1039 (3) ◽  
pp. 290-296 ◽  
Author(s):  
Alexander P. Demchenko ◽  
Oksana I. Rusyn ◽  
Alexey M. Egorov ◽  
Vladimir I. Tishkov
Keyword(s):  
Solvent Effects ◽  
Formate Dehydrogenase ◽  
Dehydrogenase Reaction ◽  
Kinetics Of
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