Solvent effects, chemical physical

Miertus S, E Scrocco and J Tomasi 1981 Electrostatic Interaction of a Solute with a Continuum - A Direct Ltilization of Ab Initio Molecular Potentials for tlie Provision of Solvent Effects. Chemical Physics 55.117-129. 

Miertus, S., E. Scrocco, and J. Tomasi, Electrostatic interaction of a solute with a continuum. A direct utilization of ab initio molecular potentials for the prevision of solvent effects. Chemical Physics, 1981. 55(1) p. 117-129. 

K. A. Chibisov and H. Corner, Complexes of spiropyran-derived merocya-nines with metal ions relaxation kinetics, photochemistry and solvent effects, Chemical Physics, vol. 237, no. 3, pp. 425—442, 1998. 

Lashkari, M. and M.R. Arshadi, DFT studies of pyridine corrosion inhibitors in electrical double layer Solvent, substrate, and electric field effects. Chemical Physics, 2004. 299(1) p. 131—137. 

Excitation followed by stimulated-emission from diabatic levels in all-trans and 15-cis-P-carotenes Effects of molecular symmetry and solvent polarity. Chemical Physics Letters, Vol. 454, No. 4-6, pp. 367-373, ISSN 0009-... 

Solvent effects on chemical equilibria and reactions have been an important issue in physical organic chemistry. Several empirical relationships have been proposed to characterize systematically the various types of properties in protic and aprotic solvents. One of the simplest models is the continuum reaction field characterized by the dielectric constant, e, of the solvent, which is still widely used. Taft and coworkers [30] presented more sophisticated solvent parameters that can take solute-solvent hydrogen bonding and polarity into account. Although this parameter has been successfully applied to rationalize experimentally observed solvent effects, it seems still far from satisfactory to interpret solvent effects on the basis of microscopic infomation of the solute-solvent interaction and solvation free energy. 

Once such effects had been noted, it became necessary to interpret the observed results and to classify the solvents. The earliest attempts at this were by Stobbe, who reviewed the effects of solvents on keto-enol tautomers [4]. Since then many attempts have been used to explain solvent effects, some based on observations of chemical reactions, others on physical properties of the solvents, and yet others on spectroscopic probes. All of these have their advantages and disadvantages and no one approach can be thought of as exclusively right . This review is organized by type of measurement, and the available information is then summarized at the end. 

As has been suggested in the previous section, explanations of solvent effects on the basis of the macroscopic physical properties of the solvent are not very successful. The alternative approach is to make use of the microscopic or chemical properties of the solvent and to consider the detailed interaction of solvent molecules with their own kind and with solute molecules. If a configuration in which one or more solvent molecules interacts with a solute molecule has a particularly low free energy, it is feasible to describe at least that part of the solute-solvent interaction as the formation of a molecular complex and to speak of an equilibrium between solvated and non-solvated molecules. Such a stabilization of a particular solute by solvation will shift any equilibrium involving that solute. For example, in the case of formation of carbonium ions from triphenylcarbinol, the equilibrium is shifted in favor of the carbonium ion by an acidic solvent that reacts with hydroxide ion and with water. The carbonium ion concentration in sulfuric acid is greater than it is in methanol-... 

The scope of this book goes beyond the proper field of solvent effects on chemical reactions. It actually goes deeper in the analysis of solvent effects as such and of chemical reactions. It also addresses the problem of mimicking chemical reactions in condensed phases and bioenvironments. The authors have gone through the problems raised by the limitations found in the theoretical representations. In order to understand, it is not sufficient to have agreement with experiments, the schemes should meet the requirements put forward by well founded physical theories. 

Therefore, one must accept that the description of the solvent effect is rather complex and cannot be simplistically made on the basis of single physical parameters. A large number of parameters (including empirical parameters) must be considered which derive from thermodynamic calculations (equilibrium constant) and kinetic calculations (rate constants) performed on a large number of chemical reactions. 

Contemporary computer-assisted molecular simulation methods and modern computer technology has contributed to the actual numerical calculation of solvent effects on chemical reactions and molecular equilibria. Classical statistical mechanics and quantum mechanics are basic pillars on which practical approaches are based. On top of these, numerical methods borrowed from different fields of physics and engineering and computer graphics techniques have been integrated into computer programs running in graphics workstations and modem supercomputers (Zhao et al., 2000). 

The following discussions of sol vent effects will pro vide further information (a) T. C. Waddington, Non-Aqueous Solvents, Thomas-Nelson, London, 1969 (b) E. M. Kosower, An Introduction to Physical Organic Chemistry, Wiley, New York, 1968, p. 259 (c) T. C. Waddington, Ed., Non-Aqueous Solvent Systems, Academic, London, 1965 (d) E. S. Amis and J. F. Hinton, Solvent Effects on Chemical Phenomena, Academic, New York, 1973 (e) J. F. Coetzee and C. D. Ritchie, Eds., Solute-Solvent Interactions, Marcel Dekker, New York, 1969 (f) A. J. Parker, Chem. Rev., 69, 1 (1969). 

The rate coefficient of a reactive process is a transport coefficient of interest in chemical physics. It has been shown from linear response theory that this coefficient can be obtained from the reactive flux correlation function of the system of interest. This quantity has been computed extensively in the literature for systems such as proton and electron transfer in solvents as well as clusters [29,32,33,56,71-76], where the use of the QCL formalism has allowed one to consider quantum phenomena such as the kinetic isotope effect in proton transfer [31], Here, we will consider the problem of formulating an expression for a reactive rate coefficient in the framework of the QCL theory. Results from a model calculation will be presented including a comparison to the approximate methods described in Sec. 4. 

Detailed and accurate descriptions of reaction mechanisms, however, have been performed for several years, in some cases with the inclusion of solvent effects. In this section we shall briefly examine some aspects of the solvation physics related to the chemical reaction mechanisms a more general discussion on chemical reactions in solution is given in the contribution by Truhlar and Pliego. 

Here we give an overview of the current status and perspectives of theoretical treatments of solvent effects based on continuum solvation models where the solute is treated quantum mechanically. It is worth noting that our aim is not to give a detailed description of the physical and mathematical formalisms that underlie the different quantum mechanical self-consistent reaction field (QM-SCRF) models, since these issues have been covered in other contributions to the book. Rather, our goal is to illustrate the features that have contributed to make QM-SCRF continuum methods successful and to discuss their reliability for the study of chemical reactivity in solution. 

The second chapter ends with two overviews by Stephens Devlin and by Hug on the theoretical and the physical aspects of two vibrational optical activity spectroscopies (VCD and VROA, respectively). In both overviews the emphasis is more on their basic formalism and the gas-phase quantum chemical calculations than on the analysis of solvent effects. For these spectroscopies, in fact, both the formulation of continuum solvation models and their applications to realistic solvated systems are still in their infancy. 

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