Evidence in favour of Exner isokinetic method to determine activation parameters

1985 ◽  
Vol 50 (7) ◽  
pp. 1565-1572
Author(s):  
Pascual Segura
Keyword(s):  
Aqueous Solution ◽  
Ab Initio ◽  
Activation Parameters ◽  
Statistical Evidence ◽  
Reaction Series ◽  
Isokinetic Relationship ◽  
Decarboxylation Reaction

Exner method to ascertain the isokinetic relationship (IKR) and obtain isokinetic activation parameters in a reaction series, although well known, is relatively little applied; A great many chemists do not appear to be convinced of the superiority of isokinetic activation parameters over conventional ones, and the IKR itself is still a controversial matter. From our kinetic results on the decarboxylation of a series of 4-substituted-2,6-dinitrobenzoate ions in aqueous solution, activation parameters were calculated, both by Exner method and by a conventional one. The obtained isokinetic activation enthalpies correlate much better (r = 0.998, 5 points) than the conventional ones (r = 0.97, 5 points), with the energies (calculated at the STO-3G ab initio level) for the formation of substituted aryl anions, the latter being a process expected to be energetically related to the decarboxylation reaction. This is the first example of non-statistical evidence in favour of Exner method to determine activation parameters, a method that we strongly advocate.

Concerning the Problem of the Isokinetic Relationship. IV. The Evaluation of the Isosubstituent Hammett Parameter by Means of Isokinetic and Isoequilibrium Temperatures

1986 ◽  
Vol 39 (2) ◽  
pp. 199 ◽  
Author(s):  
W Linert
Keyword(s):  
Temperature Dependence ◽  
Activation Parameters ◽  
Common Point ◽  
Isokinetic Temperature ◽  
Benzoic Acids ◽  
Reaction Series ◽  
Isokinetic Relationship ◽  
The Common ◽  
Point Of Intersection ◽  
Hammett Parameter

The interrelation between the isosubstituent and the isokinetic relationship is developed and tested for several Hammett reaction series. Two methods of approach to relate the temperature dependence of Arrhenius and Hammett plots are given, one utilizing the isoequilibrium temperature of the ionization of benzoic acids and the other the isokinetic temperature of the respective Hammett reaction series. The efficiency of the approaches for the evaluation of the coordinates of the common point of intersection in the Hammett plot, i.e. the characteristics of the isosubstituent relationship, are compared with each other and with experimental results. With the former approach, by using the activation parameters of only one (commonly the unsubstituted ) member of the series, the temperature dependence of a Hammett line can be predicted provided that the isokinetic temperature of the Hammett series does not approach the experimental temperature range. Otherwise the latter approach must be used which, however, needs the temperature dependence of at least two (or better more) members of the reaction series.

Kinetics and mechanism of the reaction of iron(III) with 6-methyl-2,4-heptanedione and 3,5-heptanedione

1990 ◽  
Vol 55 (8) ◽  
pp. 1984-1990 ◽  
Author(s):  
José M. Hernando ◽  
Olimpio Montero ◽  
Carlos Blanco
Keyword(s):  
Aqueous Solution ◽  
Metal Ion ◽  
Activation Parameters ◽  
Enol Form ◽  
Kinetics And Mechanism ◽  
Kinetic Constants ◽  
Steric Factors ◽  
Kinetics Of ◽  
Mechanism Of The Reaction

The kinetics of the reactions of iron(III) with 6-methyl-2,4-heptanedione and 3,5-heptanedione to form the corresponding monocomplexes have been studied spectrophotometrically in the range 5 °C to 16 °C at I 25 mol l-1 in aqueous solution. In the proposed mechanism for the two complexes, the enol form reacts with the metal ion by parallel acid-independent and inverse-acid paths. The kinetic constants for both pathways have been calculated at five temperatures. Activation parameters have also been calculated. The results are consistent with an associative activation for Fe(H2O)63+ and dissociative activation for Fe(H2O)5(OH)2+. The differences in the results for the complexes of heptanediones studied are interpreted in terms of steric factors.

Ab initio QM/MM dynamics of anion–water hydrogen bonds in aqueous solution

2005 ◽  
Vol 403 (4-6) ◽  
pp. 314-319 ◽  
Author(s):  
Anan Tongraar ◽  
Bernd Michael Rode
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Bonds ◽  
Ab Initio ◽  
Water Hydrogen

[3,3] Sigmatropic Rearrangement of Some Fluorinated 1,5-Hexadienes

2002 ◽  
Vol 67 (10) ◽  
pp. 1517-1532 ◽  
Author(s):  
William R. Dolbier ◽  
Keith W. Palmer ◽  
Feng Tian ◽  
Piotr Fiedorow ◽  
Andrzej Zaganiaczyk ◽  
...  
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Transition States ◽  
Activation Parameters ◽  
Sigmatropic Rearrangement ◽  
Semiempirical Methods ◽  
Cope Rearrangement ◽  
Computational Studies ◽  
Stepwise Mechanism ◽  
Radical Intermediates

Fluorine atoms incorporated into 1,5-hexadiene molecule should influence the kinetic as well as the thermodynamic parameters of [3,3] sigmatropic rearrangement (Cope rearrangement). Within few decades is has been documented that this transformation proceeds in a concerted manner, rather than stepwise with some radical intermediates involved. Few new terminally fluorinated 1,5-hexadienes (compounds 3, 5A, 7, 9 and 5B) have been synthesized. The activation parameters of rearrangement have been determined and compared with those known for hydrocarbon analogues. While systems developing chair-like transition states (compounds 3 and 5) showed close similarity with hydrocarbon analogues (compound 1), those developing boat-like transition states (compounds 7, 9 and 5B) may proceed through radical stepwise mechanism. Computational studies of the transition states were carried out, showing that only ab initio methods (MP2 and especially DFT) can give approximate correlation with experimental data, whereas in the case of hydrocarbon analogues even simple semiempirical methods (AM1) were reliable enough to reproduce experimental results.

scholarly journals A Study on the Kinetics and Mechanism of the One-Pot Formation of 3,4,5-Substituted Furan-2(5H)-Ones in the Presence of Lactic Acid: Effect of Different Substituents

2018 ◽  
Vol 43 (3-4) ◽  
pp. 286-299 ◽  
Author(s):  
Osman Asheri ◽  
Sayyed Mostafa Habibi-Khorassani ◽  
Mehdi Shahraki
Keyword(s):  
Lactic Acid ◽  
Activation Parameters ◽  
General Mechanism ◽  
Common Mechanism ◽  
Substituted Anilines ◽  
One Pot ◽  
Isokinetic Relationship ◽  
Zero Order Kinetics ◽  
Different Temperatures ◽  
The One

The kinetics of the reaction between para-substituted anilines and dimethyl acetylenedicarboxylate (DMAD) with derivatives of benzaldehyde for the one-pot formation of 3,4,5-substituted furan-2(5 H)-ones in the presence of lactic acid as a catalyst have been studied spectrophotometrically at different temperatures. A mechanism involving four steps was proposed for the reactions, all of which followed second-order kinetics. The partial orders with respect to substituted aniline and DMAD were one and one and the reactions revealed zero-order kinetics for benzaldehyde and its derivatives. Changing of substituents on benzaldehyde left rates of reaction unaffected. However, various substituents on aniline showed that para electron-withdrawing groups decreased the rate of reaction. According to investigation of an isokinetic relationship, a common mechanism exists for all studied substituents and a general mechanism can be formulated. Kinetic values ( k and Ea) and associated activation parameters (Δ G‡, Δ S‡ and Δ H‡) of the reactions were determined.

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