Hydride transfer reactions. Substituent effects in oxidation of N-benzylacridans by π acceptors

1983 ◽  
Vol 61 (11) ◽  
pp. 2544-2551 ◽  
Author(s):  
Allan K. Colter ◽  
Charles C. Lai ◽  
Terry W. Williamson ◽  
Raymond E. Berry
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Second Order ◽  
Face To Face ◽  
Order Rate ◽  
Linear Free Energy ◽  
Donor And Acceptor ◽  
Kinetics Of

The kinetics of oxidation of a series of eight N-(substituted benzyl)acridans (3, NBA's) by 1,4-benzoquinone (BQ), p-chloranil (CA), 2,3-dicyano-1,4-benzoquinone (DCBQ), 7,7,8,8-tetracyanoquinodimethane (TCNQ), and tetracyanoethylene (TCNE) in acetonitrile (AN) and by BQ in 50:50 (v/v) AN-water were measured at 25 °C. Equilibrium constants for pseudobase formation, [Formula: see text], from the corresponding acridinium ions (4) were measured in water at 25 °C. Hammett correlations of the second-order rate constants for reaction of the NBA's without ortho substitutents (3a–e) led to ρ values of −0.29 (BQ, AN), −0.55 (CA), −0.56 (DCBQ), −0.64 (TCNQ), −0.41 (TCNE), and −0.47 (BQ, 50:50 AN–water). The second-order rate constants for 3a–e also give good linear free energy correlations with the [Formula: see text] values of 4a–e. These correlations and the [Formula: see text] values for the ortho-substituted acridinium ions (4f, g, h) are used to calculate rate constants for oxidation of the corresponding ortho-substituted NBA's (3f, g, h). The rate constants calculated in this way are 4.7 to 6.6 times and 6.4 to 12 times larger, respectively, than the observed rate constants for N-(2,4,6-trimethylbenzyl) and N-(2,6-dichlorobenzyl)acridan (3g and h). The variations in ρ values are attributed mainly to differences in the amount of electrostatic stabilization in the transition state resulting from differences in the separation of donor and acceptor and the degree of delocalization of the negative charge. The rate retarding effect of a pair of ortho substituents is attributed to sterie effects in a preferred face-to-face transition state.

Determination of the Nucleophilicity of Tricarbonyliron Coordinated Cyclohepta-1,3,5-triene

1999 ◽  
Vol 64 (11) ◽  
pp. 1770-1779 ◽  
Author(s):  
Herbert Mayr ◽  
Karl-Heinz Müller
Keyword(s):  
Gibbs Energy ◽  
Ambient Temperature ◽  
Rate Constants ◽  
Second Order ◽  
Order Rate ◽  
Electrophilic Additions ◽  
Kinetics Of

The kinetics of the electrophilic additions of four diarylcarbenium ions (4a-4d) to tricarbonyl(η4-cyclohepta-1,3,5-triene)iron (1) have been studied photometrically. The second-order rate constants match the linear Gibbs energy relationship log k20 °C = s(E + N) and yield the nucleophilicity parameter N(1) = 3.69. It is concluded that electrophiles with E ≥ -9 will react with complex 1 at ambient temperature.

KINETICS OF THE AQUEOUS ALKALINE HOMOGENOUS HYDROLYSIS OF HIGH EXPLOSIVE 1, 3,5,7-TETRAAZA- 1, 3,5,7-TETRANITROCYCLOOCTANE (HMX)

1994 ◽  
Vol 30 (3) ◽  
pp. 53-61 ◽  
Author(s):  
Harro M. Heilmann ◽  
Michael K. Stenstrom ◽  
Rolf P. X. Hesselmann ◽  
Udo Wiesmann
Keyword(s):  
Temperature Dependence ◽  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Elevated Temperatures ◽  
Second Order ◽  
Order Rate ◽  
Subsequent Calculation ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Order Rate Equation

In order to get basic data for the design of a novel treatment scheme for high explosives we investigated the kinetics for the aqueous alkaline hydrolysis of 1,3,5,7-tetraaza-1,3,5,7-tetranitrocyclooctane (HMX) and the temperature dependence of the rate constants. We used an HPLC procedure for the analysis of HMX. All experimental data could be fit accurately to a pseudo first-order rate equation and subsequent calculation of second-order rate constants was also precise. Temperature dependence could be modeled with the Arrhenius equation. An increase of 10°C led to an average increase in the second-order rate constants by the 3.16 fold. The activation energy of the second-order reaction was determined to be 111.9 ±0.76 kJ·moJ‒1. We found the alkaline hydrolysis to be rapid (less than 2.5% of the initial HMX-concentration left after 100 minutes) at base concentrations of 23 mmol oH‒/L and elevated temperatures between 60 and 80°C.

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.

AM1 calculational and experimental evidence that a β-nitroxyl group significantly enhances the thermodynamic and kinetic acidities of ketones

1994 ◽  
Vol 72 (11) ◽  
pp. 2348-2350 ◽  
Author(s):  
Nick Henry Werstiuk ◽  
Chandra Deo Roy
Keyword(s):  
Experimental Evidence ◽  
Gas Phase ◽  
Carbonyl Group ◽  
Rate Constants ◽  
Second Order ◽  
Nitroxyl Group ◽  
Order Rate ◽  
Kinetics Of

The kinetics of NaOD-catalysed H/D exchange of 3,3,5,5-tetramethylcyclohexanone (1), 1-hydroxy-4-oxo-2,2,6,6-tetrame-thylpiperidine (2), 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl (3), 9-hydroxynorpseudopelletierine (4), and norpseudopelle-tierine-9-oxyl (5) have been studied in 60:40 dioxane–D2O(v/v) at 25.0 °C. The second-order rate constants are 9.20 × 10−3, 6.39 × 10−2, 1.59, 2.20 × 10−2, and 5.67 × 10−1 L mol−1 s−1 for 1, 2, 3, 4, and 5, respectively. Gas-phase enthalpies of ionization (the values are 363.0, 359.4, 352.0, 360.7, and 354.1 kcal mol−1 for 1, 2, 3, 4, and 5, respectively) calculated with AM1 correlate with the relative rates of enolization. Thus replacement of the β-hydroxylamino groups of 2 and 4 with a nitroxyl group produces sizable increases in the kinetic and thermodynamic acidities of the hydrogens α to the carbonyl group.

Kinetik der Reaktion von Papain mit Bromacetamid / Kinetics of the reaction of papain with bromoacetamide

1971 ◽  
Vol 26 (1) ◽  
pp. 43-46 ◽  
Author(s):  
Hans-Gerhard Löffler ◽  
Friedhelm Schneider ◽  
Helmut Wenck
Keyword(s):  
Rate Constants ◽  
Turning Point ◽  
Ph Dependence ◽  
Activation Parameters ◽  
Second Order ◽  
Order Rate ◽  
Ph Range ◽  
Kinetics Of

The pH-dependence of the second order rate constants of the reaction of papain with bromoacetamide in the pH-range 5,5-8,5 is described by a curve with a turning point corresponding to a pK 7,3 ± 0,1 at 25°. This is the pK of a catalytically essential imidazole residue. The activation parameters of the reaction of papain with bromoacetamide were determined. The second order rate constants at pH 7 for the reaction is 200 times greater than for the reaction of bromoacetamide with simple SH-compounds.

Effect of pH on the reaction of 1,3-dihydro-1-hydroxy-3-oxo-1,2-benziodoxole with 2-mercaptoethanol, 2-mercaptoethylamine, and glutathione

1970 ◽  
Vol 48 (19) ◽  
pp. 3104-3107 ◽  
Author(s):  
James Leslie
Keyword(s):  
Rate Constants ◽  
Ionic Species ◽  
Second Order ◽  
Hydrogen Ion ◽  
Effect Of Ph ◽  
Order Rate ◽  
Rate Determining Step ◽  
Ion Activity ◽  
Kinetics Of ◽  
Linear Manner

The kinetics of the oxidation of 2-mercaptoethanol, 2-mercaptoethylamine, and glutathione with 1,3-dihydro-1-hydroxy-3-oxo-1,2-benziodoxole (1) have been examined at pH 4–5.6. The reaction is second-order, which can be explained by a rate-determining step involving the reaction of one molecule of the thiol with one molecule of 1. The second-order rate constants vary in a linear manner with the reciprocal of the hydrogen ion activity. The ionic species involved in the reaction are discussed.

Primary isotope effects and mechanism of base initiated β-elimination reactions of di-(p-nitrophenyl)fluoroethanes

1977 ◽  
Vol 55 (10) ◽  
pp. 1696-1700 ◽  
Author(s):  
Jan Kurzawa ◽  
Kenneth T. Leffek
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Sodium Methoxide ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Second Order ◽  
Order Rate ◽  
Elimination Reactions

The second-order rate constants have been determined for the β-elimination reactions of 2,2-di-(p-nitrophenyl)-1,1,1-trifluoroethane, 2,2-di-(p-nitrophenyl)-1-fluoroethane, and their β-deuterated analogues with sodium methoxide in methanol. The primary isotope effects and activation parameters for these reactions are reported. It is suggested that the trifluoro-compound reacts via the pre-equilibrium carbanion mechanism (ElcB)R and that the monofluoro compound follows the E2 mechanism via a carbanion-like transition state.

scholarly journals Determination of the Mechanism of Nucleophilic Reaction of Fenitrothion Using Substituted Phenoxide Nucleophiles in Aqueous Media

2021 ◽  
pp. 40-46
Author(s):  
E. G. Amadi ◽  
C. I. Egwuatu ◽  
C. U. Okoro ◽  
F. O. Obumselu ◽  
M. U. Onuoha
Keyword(s):  
Transition State ◽  
Rate Constant ◽  
Aqueous Media ◽  
Order Rate Constant ◽  
Second Order ◽  
Bond Rupture ◽  
Linear Free Energy Relationship ◽  
Order Rate ◽  
Linear Free Energy ◽  
Nucleophilic Displacement

The mechanism of the nucleophilic displacement reaction at the phosphorus centre of organophosphates was determined. Phenoxide nucleophiles were reacted with fenitrothion (O,O-dimethyl O-(3-methyl-4-nitrophenyl) phosphorothioate) in water at 25oC and pseudo-first order rate constant measurements taken. Second-order rate constant (kNuc) was determined for the different concentrations of nucleophiles while the second-order rate constant (klg) for the investigation of 2,4-dichlorophenoxide ion with and series of aryl phosphorothioate esters was also determined. Linear free energy relationship was further determined using the Brϕnsted-type plot. The plots are linear over a range of pKaNuc of 7.15-11.10 that straddles the pKa of the leaving 3-methyl-4-nitrophenoxide ion (pKa = 7.20) with statistically acceptable linear correlations (R2 = 0.987) and (R2 = 0.980). The linearity in the traditional Brϕnsted-type plots shows the sensitivity of the nucleophilic displacement to the basicity of the nucleophiles and hence is consistent with a single transition-state mechanism whose barrier to decomposition is low hence concerted. Analysis of the values of βNuc, βLg and βeq (0.734) with the effective charge distribution in the transition state shows that it has no positive character. The Leffler index presents bond formation being slightly ahead of bond rupture.

Experimental and AM1 calculational studies of the deprotonation of bicyclo[2.2.2]octane-2,5-dione and bicyclo[2.2.2]octane-2,6-dione: a study of homoconjugation, inductive, and steric effects on the rates and diastereoselectivities of α enolization

1995 ◽  
Vol 73 (3) ◽  
pp. 460-463
Author(s):  
Nick Henry Werstiuk ◽  
Chandra Deo Roy
Keyword(s):  
Carbonyl Group ◽  
Rate Constants ◽  
Second Order ◽  
Polar Effect ◽  
Steric Effects ◽  
Order Rate ◽  
Kinetics Of

The kinetics of NaOD-catalyzed H/D exchange (enolization) at C3 α to the carbonyl group of bicyclo[2.2.2]octane-2,5-dione (1) and bicyclo[2.2.2]octane-2,6-dione (2) have been studied in 60:40 (v/v) dioxane–D2O at 25.0 °C. The second-order rate constants for exchange are (9.7 ± 1.5) × 10−1 and (3.4 ± 1.2) × 10−5 L mol−1 s−1 for 1 and 2, respectively. Thus, 1, exchanges 76 times faster than bicyclo[2.2.2]octan-2-one (3) (k = (1.27 ± 0.02) × 10−2 L mol−1 s−1), but the 2,6-dione 2 unexpectedly is much less reactive (2.7 × 10−3) than the monoketone. Unlike the large exo selectivity of 658 observed in the case of bicyclo[2.2.1]heptan-2-one, small and opposite selectivities, exo (1.2) for 1 and endo (2.1) for 2, are found for the isomeric [2.2.2] ketones. The results indicate that the incipient enolate of 1 is stabilized by a polar effect of the β carbonyl group at C5, not by homoconjugation. The source of the surprising low reactivity of 2 is unknown at this stage. The small diastereoselectivities, exo (1.2) for 1 and endo (2.1) for 2, correlate with relative energies of the diastereomeric pyramidal enolates calculated with AM1. Keywords: enolization, bicyclo[2.2.2]octane-2,5-dione, bicyclo[2.2.2]octane-2,6-dione, AM1, thermodynamic acidities.

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