Solvent effects hydrogen bond accepting

Even for a simple reaction, involving just one reactant species and one product species, such as a keto-enol tautomerism or a cis-trans isomerization, the above equation for a given solvent is complicated. StUl, in specific cases it is possible to unravel the solvent effects of cavity formation, for the solute species have different volumes, polarity/polarizability if the solute species differ in their dipole moments or polarizabilities, and solvent Lewis acidity and basicity if the solutes differ in their electron-pair and hydrogen-bond acceptance abilities. 

Less is known about the relative Importance of solvent-solute hydrogen bonding in affecting solvent selectivity, although several workers have postulated such effects (e.g., /. 42, 43). However, one must be cautious in accepting these various observations at face value, because solvent-solute localization effects will normally be large in systems that can ex-... 

The three parameters that are central to the method are tt, a, and The tv parameter provides a comprehensive measure of the ability of a solvent to stabilize a solute molecule based on the dielectric effects. It is a quantitative index of solvent dipolarity and polarizability. The acidity a for a solvent is a measure of its strength as a hydrogen-bond donor HBD, its ability to donate a proton in a soIvent-to-solute hydrogen bond. The estimation of a is based on the experimental determination of n and t(30). The t(30) scale, developed by Reichardt et al., indicates a solvent strength by combining polarity and HBD acidity, which itself serves as a useful solvent parameter for physicochemical correlations in a wide range of solvents. ° The basicity parameter denotes the solvent s hydrogen-bond acidity HBA or an index of the solvent s ability to accept a proton in a... 

In the previous part we showed that hydrogen bonding may lead to rate accelerations and increased selectivities. The effects of pure hydrogen bonding of suitable additives is most evident in non-polar solvents, because of the competition of H-bond accepting solvents and the reactants. Water exhibits some other solvent effects derived from its special properties, as discussed below. 

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