The Enthalpy‐Entropy Relationship

Exner, Otto

doi:10.1002/9780470171899.ch6

Cited by 254 publications

(31 citation statements)

References 139 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Although all the possible xÀy planes that can be drawn with these four parameters exhibit similar FD lines, we have selected the spectroscopic scale as the reference abscissa to prevent all bias due to the possible compensation effects between thermodynamic scales. [54,55] Much important information can be obtained from this figure. The first concerns the validity of the so-called "Badger-Bauer correlation" [56,57] between the enthalpy of the association and the frequency shift, which has been the object of many controversies in the literature over several decades.…”

Section: Resultsmentioning

confidence: 98%

A Theoretical Evaluation of the pK_HBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

Besseau

Graton

Berthelot

2008

Chemistry A European J

View full text Add to dashboard Cite

The experimental pKHB hydrogen-bond (HB) basicity scale and the corresponding DeltaH[symbol: see text]HB enthalpic scale of nitrogen compounds are extended and analysed in light of simple theoretical descriptors using the B3LYP density functional method and a medium-size basis set (6-31+G(d,p)).The selected training set includes 59 monofunctional unhindered nitrogen bases for which homogeneous and accurate experimental pKHB and DeltaH[symbol: see text]HB data have been determined by means of the association equilibrium of the bases with a reference hydrogen-bond acid, 4-fluorophenol, in CCl4. The three hybridisation states encountered in the nitrogen atom, sp, sp2 and sp3, are equally represented in this data set. A proper estimation of their experimental enthalpy (DeltaH[symbol: see text]HB) is directly attainable from the theoretical enthalpy of the complexation reaction with hydrogen fluoride (DeltaH[symbol: see text](HF)). However, a second parameter is required to calculate with good accuracy the experimental free energy of association represented by pKHB. About 99% of the variance of the pKHB scale is described by a bilinear equation using the minimum electrostatic potential (Vs,min) of the monomer in addition to the interaction energy (D0(HF). The equations are tested for an external set of 99 additional compounds including very different nitrogen bases such as ortho-substituted pyridines, polyazines and azoles.Theoretical calculations give a reliable estimation of hydrogen-bond basicity provided that the populations of the different isomers of the bases are taken into account by using the Boltzmann law, and that a specific halogen-bond interaction with the solvent CCl4 is considered for polybasic molecules.The pKHB scale can thus be extended to important classes of species experimentally inaccessible in CCl4, to polynitrogen compounds and to molecules of biological significance.

show abstract

Section: Resultsmentioning

confidence: 98%

A Theoretical Evaluation of the pK_HBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

Besseau

Graton

Berthelot

2008

Chemistry A European J

View full text Add to dashboard Cite

show abstract

“…This type of behavior might be an indication that enthalpy-entropy compensation effect does not operate in such systems [27]. According to Exner [28], a criterion for the existence of a compensation effect is the linear relationship of kinetic constants at two temperatures: where k 3T1 and log k 3T2 are kinetic constants at two different temperatures T 1 and T 2 . The slope b is related to the isokinetic temperature (Φ) by the following equation:…”

Section: Resultsmentioning

confidence: 99%

Enthalpy-Entropy Compensation in Polyester Degradation Reactions

Al‐Mulla

2012

International Journal of Chemical Engineering

View full text Add to dashboard Cite

In an earlier work the author had studied the degradation kinetics of polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), and polybutylene terephthalate (PBT) under nonisothermal conditions in air and N 2 at heating rates of 5, 10, 15, and 20• C/min. In this paper the kinetic degradation parameters of PET, PTT, and PBT were estimated using the CoatsRedfern method for two different weight loss regions ranging from 2-8% (Zone I) and 8-40% (Zone II). A comparative analysis of the enthalpy-entropy compensation effect for these polyesters in air and N 2 is presented. A linear relationship was found to exist between entropy and enthalpy values. The following criteria were applied to establish an enthalpy-entropy compensation effect and to check the presence of an isokinetic temperature: (a) Exner's plot of log k 3T1 versus log k 3T2 , and (b) Krug et al. linear regression of ΔH versus ΔG. By the use of the latter two methods, varying isokinetic temperatures were obtained. These temperatures were not in the range of the experimental work conducted, indicating that these systems do not display compensation phenomena.

show abstract

“…Moreover, Leffler's approach was criticized by Peterson, who stated that a liner enthalpy‐entropy plot is deceptive and is not sufficient to support the concept of the isokinetic relationship. In view of this criticism, we have used Exner's equation to obtain “isokinetic temperature” ( β) values for various systems in this study. The isokinetic relationship is tested by plotting the logarithms of rate constants at two different temperatures ( T 2 > T 1 ) against each other according to Equation :

false(β false) = [T_{1} T_{2} (b) / (T_{2} b - T_{1})] (when T_{2} > T_{1}) .

Here T 1 and T 2 represent any two reaction temperatures of the experimental study, and T 2 > T 1 ; ( b ) is the slope obtained from the linear plot of log k (at T 2 ) versus log k (at T 1 ), according to the following equation:

log k false(at T_{2} false) = false(b false) log k false(at T_{1} false) .

Obtained “isokinetic temperature” ( β) value for (TCCA‐NaNO 2 ) system (β) is 403.7K, (TCCA‐DMF)/NaNO 2 system (β) is 365.8K, and (TCCA‐DMA)/NaNO 2 system (β) is 358.0 K.…”

Section: Resultsmentioning

confidence: 99%

Kinetics and mechanism of trichloroisocyanuric acid/NaNO₂‐triggered nitration of aromatic compounds under acid‐free and Vilsmeier‐Haack conditions

Muddam

Rajanna

Govardhan

et al. 2019

Int J of Chemical Kinetics

View full text Add to dashboard Cite

Kinetics and mechanism of nitration of aromatic compounds using trichloroisocyanuric acid (TCCA)/NaNO2, TCCA‐N,N‐dimethyl formamide (TCCA‐DMF)/NaNO2, and TCCA‐N,N‐dimethyl acetamide (TCCA‐DMA)/NaNO2 under acid‐free and Vilsmeier‐Haack conditions. Reactions followed second‐order kinetics with a first‐order dependence on [Phenol] and [Nitrating agent] ([TCCA], [(TCCA‐DMF)], or [(TCCA‐DMA)] >> [NaNO2]). Reaction rates accelerated with the introduction of electron‐donating groups and retarded with electron‐withdrawing groups, but did not fit well into the Hammett's theory of linear free energy relationship or its modified forms like Brown‐Okamoto or Yukawa‐Tsuno equations. Rate data were analyzed by Charton's multiple linear regression analysis. Isokinetic temperature (β) values, obtained from Exner's theory for different protocols, are 403.7 K (TCCA‐NaNO2), 365.8 K (TCCA‐DMF)/NaNO2, and 358 K (TCCA‐DMA)/NaNO2. These values are far above the experimental temperature range (303‐323 K), indicating that the enthalpy factors are probably more important in controlling the reaction.

show abstract

The Enthalpy‐Entropy Relationship

Cited by 254 publications

References 139 publications

A Theoretical Evaluation of the pK_HBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

A Theoretical Evaluation of the pK_HBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

Enthalpy-Entropy Compensation in Polyester Degradation Reactions

Kinetics and mechanism of trichloroisocyanuric acid/NaNO₂‐triggered nitration of aromatic compounds under acid‐free and Vilsmeier‐Haack conditions

Contact Info

Product

Resources

About

The Enthalpy‐Entropy Relationship

Cited by 254 publications

References 139 publications

A Theoretical Evaluation of the pKHBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

A Theoretical Evaluation of the pKHBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

Enthalpy-Entropy Compensation in Polyester Degradation Reactions

Kinetics and mechanism of trichloroisocyanuric acid/NaNO2‐triggered nitration of aromatic compounds under acid‐free and Vilsmeier‐Haack conditions

Contact Info

Product

Resources

About

A Theoretical Evaluation of the pK_HBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

A Theoretical Evaluation of the pK_HBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

Kinetics and mechanism of trichloroisocyanuric acid/NaNO₂‐triggered nitration of aromatic compounds under acid‐free and Vilsmeier‐Haack conditions