Solvent effects on chemical

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. 

Among many examples of the solvent effects on chemical equilibria and reactions, the solvent effect on tautomerization has been one of the most extensively studied. Experi-... 

Amis, E. S., and Hinton, J. F., Solvent Effects on Chemical Phenomena, Academic Press, New York, 1973. 

Before considering the analysis of solvent effects on chemical reactions, some of the shortcomings of potential energy hypersurfaces as a tool to describe chemical process are... 

The several theoretical and/or simulation methods developed for modelling the solvation phenomena can be applied to the treatment of solvent effects on chemical reactivity. A variety of systems - ranging from small molecules to very large ones, such as biomolecules [236-238], biological membranes [239] and polymers [240] -and problems - mechanism of organic reactions [25, 79, 223, 241-247], chemical reactions in supercritical fluids [216, 248-250], ultrafast spectroscopy [251-255], electrochemical processes [256, 257], proton transfer [74, 75, 231], electron transfer [76, 77, 104, 258-261], charge transfer reactions and complexes [262-264], molecular and ionic spectra and excited states [24, 265-268], solvent-induced polarizability [221, 269], reaction dynamics [28, 78, 270-276], isomerization [110, 277-279], tautomeric equilibrium [280-282], conformational changes [283], dissociation reactions [199, 200, 227], stability [284] - have been treated by these techniques. Some of these... 

Tapia, O. and Lluch, J. M. Solvent effects on chemical reaction profiles. Monte Carlo simulation of hydration effects on quantum chemically calculated stationary structures, J. Chem.Phys., 83 (1983, 3970-3982... 

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. 

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). 

Tapia, O. and Bertran, J. 1996. Solvent Effects on Chemical Reactivity, Kluwer Dordrecht. 

This book was written to provide readers with some knowledge of electrochemistry in non-aqueous solutions, from its fundamentals to the latest developments, including the current situation concerning hazardous solvents. The book is divided into two parts. Part I (Chapters 1 to 4) contains a discussion of solvent properties and then deals with solvent effects on chemical processes such as ion solvation, ion complexation, electrolyte dissociation, acid-base reactions and redox reactions. Such solvent effects are of fundamental importance in understanding chem-... 

The classification of solvents has been dealt with in various books on non-aque-ous solvents [25, 26]. In the classification of solvents, it is usual to use some solvent properties as criteria. In order to discuss solvent effects on chemical reactions, it is convenient to use relative permittivities and acid-base properties as the criteria. 

The various factors that contribute to ion solvation were discussed in Section 2.2.1. In this section, we deal with the solvent effects on chemical reactions more quantitatively [5, 22]. To do this, we introduce two quantities, the Gibbs energy of transfer and the transfer activity coefficient. 

We can use the transfer activity coefficients to predict solvent effects on chemical reactions and equilibria [22]. Some examples are shown below. 

Khossravi, D., and K. A. Connors, Solvent effects on chemical processes. I Solubility of aromatic and heterocyclic compounds in binary aqueous-organic solvents , J. Pharm. Sci., 81, 371-379 (1992). 

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). 

In the last few years, the polarizable continuum model for the study of solvation has been extended to consider multideterminantal wavefunctions. Such novel techniques allow the study of the most important solvent effects on chemical reactions. In this context, the valence bond theory provides a way to analyze such effects through the transcription of the, generally, complicated multiconfigurational wavefunctions into sums of few selected classical structures, which are, in fact, more useful to understand the electron distribution rearrangement along a reaction path. In this chapter, the valence bond analysis of CASSCF wavefunctions calculated for chemical reactions in solution is discussed in details. By way of example, the results for some basic chemical processes are also reported. 

The development of the MPE method opened an avenue to the theoretical analysis of solvent effects on chemical and physico-chemical properties. The method was intensively applied to spectroscopical properties in the 1980s [28] including NMR nuclear quadrupole coupling [29,30], spin-spin coupling constants [31], IR spectra [28,32-34] vibrational polarizabilities [35], as well as UV-V and circular dichroism spectra [36-38],... 

It is assumed that all the explanatory variables are independent of each other and truly additive as well as relevant to the problem under study [144], MRA has been widely used to establish linear Gibbs energy (LGE) relationships [144, 149, 150], The Hammett equation is an example of the simplest form of MRA, namely bivariate statistical analysis. For applications of MRA to solvent effects on chemical reactions, see Chapter 7.7. 

For many physical organic chemists, the Menschutkin reaction was a kind of guinea pig , which has been extensively used for the study of solvent effects on chemical reactivity. A comprehensive review of this reaction has been given by Abboud el al. [786], More recent theoretical treatments of the solvent influence on Menschutkin reactions can be found in references [787-789]. 

---