Hydrogen bonding acidity and basicity

The difference in the hydrogen bond acidities and basicities was far more marked. The a value is largely determined by the availability of hydrogen bond donor sites on the cation. Values range from 0.8-0.9 for the monoalkylammonium salts, and are slightly lower (0.3-0.8) for the imidazolium salts. In the absence of a... 

Overall, we have shown that family-independent correlations can be obtained for solute hydrogen bond acidity and basicity, as quantitated by a 1 and log KHB. These are well represented at the HF/6-31G level by an electrostatic potential term alone, V or V, . , respectively (Hagelin et al. 1995). 

The accurate determination of gas-phase basicities and gas-phase acidities opened the way to analyses of the effect of solvation on proton acidities, and on hydrogen-bond acidities and basicities, as well as on substituents effects. 

Zhao and coworkers [53] also constructed a linear model using the Abraham descriptors. The MLR model possesses good correlation and predictability for external data sets. In this equation, E is an excess molar refraction (cm3/mol/ 10.0) and S the dipolarity/polarizability, A and B are the hydrogen bond acidity and basicity, respectively, and V is the McGowan characteristic volume (cm3/ mol/100). The large coefficients of A and B indicate too polar molecules having poor absorption. 

Here E is the solute excess molar refractivity, S is the solute dipolarity/ polarizability A and B are the overall or summation hydrogen-bond acidity and basicity, respectively and V is the McGowan characteristic volume lower-case letters stand for respective coefficients which are characteristic of the solvent, c is the constant. By help of sfafisfical methods like the principal component analysis and nonlinear mapping, the authors determined the mathematical distance (i.e., measure of dissimilarify) from an IL fo seven conventional solvents immiscible with water. It appears that the closest to the IL conventional solvent is 1-octanol. Even more close to IL is an aqueous biphasic system based on PEG-200 and ammonium sulfate (and even closer are ethylene glycol and trifluoroethanol, as calculated for hypofhefical water-solvenf sysfems involving fhese solvenfs). 

During the last 15 years, Abraham and his co-workers have established a set of five descriptors for the general description of logarithmic partition coefficients by linear regression. Their so-called linear free energy relationship (LFER) descriptors E, S, A, B, and V are effective parameters for the polarizability, polarity, hydrogen-bond acidity and basicity, and volume of the solute molecules, respectively [113-116]. They are mainly derived from experimental refraction and partition coefficients of the solutes. 

In this equation, R, is the excess molar refraction iTs is the dipolarity/polarizability 2 and E jSp. are the summation of hydrogen bond acidity and basicity values, respectively and Vx is McClowan s volume. 

Abraham developed what is termed a general solvation equation. The main idea behind the model involves the creation of a cavity in the solvent, incorporation of the solvent in the cavity, and turning on solute-solvent interactions. These interactions require a relevant solute parameter, and the ones chosen were the excess molar refraction, ttf the solute dipolarity/polarizability, flf and Pf the hydrogen-bond acidity and basicity, respectively, and a characteristic volume. Applying this general equation to 132 solutes in aqueous SDS, Abraham et al. obtained the following equation for the partition coefQcient ... 

Electrotopological indices have been used to predict permeability, computationally (Table 16-3). The electrotopological descriptors are not always easily comprehended, even though they can be attributed to describe hydropho-bicity, hydrophilicity, and size. Other typical 2D generated descriptors are related to dispersion forces, polarizability, solute molar volume, and hydrogen bonding acidity and basicity [44-47]. Descriptors such as log Poct/log Doct,... 

This analysis suggests that the QSPR relationship for chranical percutaneous absorption in the biologically intact IPPSF requires five descriptors that arc similar in nature to those prcviously used for in vitro models. Because all QSPR models utilize diffeimt chranicals and exposure conditions, it is hard to mechanistically compare these IPPSF results to earUer attempts. For example, molecular volume and hydrogen bond acidity and basicity were sufficient in the Potts and Guy (1995)... 

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