Free-energy relationship

Summary

In physical organic chemistry, a free-energy relationship or Gibbs energy relation relates the logarithm of a reaction rate constant or equilibrium constant for one series of chemical reactions with the logarithm of the rate or equilibrium constant for a related series of reactions. Free energy relationships establish the extent at which bond formation and breakage happen in the transition state of a reaction, and in combination with kinetic isotope experiments a reaction mechanism can be determined. Free energy relationships are often used to calculate equilibrium constants since they are experimentally difficult to determine. The most common form of free-energy relationships are linear free-energy relationships (LFER). The Brønsted catalysis equation describes the relationship between the ionization constant of a series of catalysts and the reaction rate constant for a reaction on which the catalyst operates. The Hammett equation predicts the equilibrium constant or reaction rate

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https://en.wikipedia.org/wiki/Free-energy_relationship

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Solvatochromic Analysis of Partition Coefficients in the o-Nitrophenyl Octyl Ether (o-NPOE)/Water System

Pierre-Alain Carrupt, Hubert Girault, Natalie Muller

The objective of this study was to unravel the structural properties responsible for the partitioning of solutes in o‐nitrophenyl octyl ether (o‐NPOE)/H2O, a new solvent system for the determination of the partition coefficients of ions. A set of 88 compounds (including drugs) was selected to allow a regular and broad distribution of property spaces. Partition coefficients in o‐NPOE/H2O (log Pnpoe) were measured by the shake‐flask or the potentiometric method. Linear solvation free‐energy relationship (LSER) analyses showed that Van der Waals volume, H‐bond‐acceptor basicity, and H‐bond‐donor acidity are the three molecular descriptors of solutes determining their log Pnpoe values. The partitioning mechanism of the investigated compounds in o‐NPOE/H2O is controlled by the same structural properties as it is in 1,2‐dichloroethane (DCE)/H2O. Δlog Poct−npoe Values (difference between log Poct and log Pnpoe) express mainly dipolarity/polarizability and H‐bond‐donor acidity. The solvent o‐NPOE is shown to be a good candidate to replace DCE in measurements of lipophilicity.

2003

Redefining solubility parameters: Bulk and surface properties from unified molecular descriptors

Vassily Hatzimanikatis

The central objective of this work is to revisit the development of the widely used solubility parameters and linear solvation energy relationships (LSER) and seek interconnections and possibilities for secure exchange of information. Partial solvation parameters (PSP) are used as the reference concept through which the unification is attempted and extended to surface tension components. Simple expressions are reported interrelating solubility parameters with LSER molecular descriptors. The fundamental differences of the various approaches to hydrogen bonding interactions are discussed in an effort to explain incompatibilities and similarities. Simple QSPR-type expressions are proposed for fast solvent screening and related properties. Predictions of drug solubilities and wetting properties of solid surfaces are reported. The developments are made by having in mind their implementation in a thermodynamic equation-of-state framework for the reliable estimation of all basic thermodynamic quantities of compounds over a broad range of external conditions. The challenges and the perspectives of this unification are critically discussed. (C) 2017 Elsevier Ltd.

Academic Press Ltd- Elsevier Science Ltd2017

A simple predictive molecular thermodynamic model for bulk phases and interfaces is presented. The model combines features of the quantitative structure-property relationships (QSPR) approach, the equation-of-state approach, and quantum-chemical calculations. Simple formalisms on a sound thermodynamic basis have been developed for the main thermodynamic quantities of pure components and mixtures while the required parameters for the calculations are rather easily obtained from common databases in the public domain. The widely available solubility parameters or the linear solvation energy relationships (LSER) molecular descriptors are exploited for the extraction of the required information. The predictive capacity of the model with a variety of properties and types of systems including highly nonideal hydrogen-bonded mixtures is reviewed. Emphasis is given in this work on predictions of solvation free energies and the results are rather satisfactory. The strength and weakness of the model and its perspectives are also critically discussed.

AMER CHEMICAL SOC2019