Hydrogen bond acceptor basicity

Kamlet, M. J., A. Solomonovici, and R. W. Taft. 1979. Linear Solvation Energy Relationships. 5. Correlations between Infrared Ar Values and the (3 Scale of Hydrogen Bond Acceptor Basicities. J. Am. Chem. Soc. 101, 3734. 

Logarithmic bioconcentration factors have been shown to be correlated with the logarithmic octa-nol/water partition coefficient in aquatic organisms (Davies and Dobbs, 1984 de Wolf et al., 1992 Isnard and Lambert, 1988) and fish (Davies and Dobbs, 1984 Kenaga, 1980 Isnard and Lambert, 1988 Neely et al., 1974 Ogata et al., 1984 Oliver and Niimi, 1985). In addition, bioconcentration factors are well correlated by a linear solvation energy relationship (coimnonly known as LSER) that includes the intrinsic solute molecular volume and solvatochromic parameters that measnre hydrogen bond acceptor basicity and donor acidity of the componnd (Park and Cho, 1993). 

The value of kd was obtained from the determination of triplet lifetimes by measuring the decay of phosphorescence and found to be insensitive to changes in solvent polarity. The k2 values derived from Eqs. 10 and 11 were correlated with solvent parameters using the linear solvation energy relationship described by Abraham, Kamlet and Taft and co-workers [18] (Eq. 12), which relates rate constants (k) to four different solvation parameters (1) or the square of the Hildebrand solubility parameter (solvent cohesive energy density), (2) n or solvent dipolarity or polarizability, (3) a, or solvent hydrogen bond donor acidity (solvent electrophilic assistance), and (4) or solvent hydrogen bond acceptor basicity (solvent nucleophilic assistance). 

For other, more recent quantitative scales of the hydrogen-bond donor acidities and hydrogen-bond acceptor basicities of solvents, see the end of Section 2.2.5 (and references [329-334] cited therein). 

P empirical parameter of solvent hydrogen-bond acceptor basicity (Taft and Kamlet) ... 

Mog a = -1.93 + 3.06 WlOO + 0.56 n -3.20(3, where Vis a measure of solute molar volume and k and P are the solva-tochromic parameters that scale dipolarity/polarizabilities and hydrogen bond acceptor basicities of the adsorbates. 

Meanwhile, fluorinated alcohols cannot be good proton acceptors due to their electron-deficient lone pairs on the oxygen atoms. The (3 scale of both TFE and HFIP is 0.00, which is apparently smaller than those of ethanol (0.77), ether (0.47), water (0.18), or even toluene (0.11) [33]. Here, the (3 scale, i.e. the hydrogen-bond acceptor basicity of a solvent, describes the ability to accept a proton (donate an electron pair) in a solute-solvent hydrogen-bonding system [4]. These acidities (pFCa [31, 34]), hydrogen-bonding parameters (a and (3 scale... 

For the analysis of SN1 solvolyses, Abraham et al. (9) have proposed an equation (equation 3) based on sensitivities toward solvatochromatic properties. In equation 3, tr is a measure of solvent dipolarity-polarization, a is a measure of solvent hydrogen bond donor acidity, and P is a measure of solvent hydrogen bond acceptor basicity. More recently, a term governing cavity effects has been added, and this term is considered to represent an important contribution (10, 11). The cavity term can be directly related to the square of the Hildebrand solubility parameter (10-12). A similar analysis by Koppel and Palm (13, 14) involves terms governed by solvent polarity, solvent polarizability, electrophilic solvation ability, and nucleophilic solvation ability. Recently, a cavity term has also been added to this analysis (12). 

Taft and coworkers described the formulation of three scales of solvent properties which were used to unravel and rationalize solvent effects on many types of physico-chemical properties. A tt scale of polarity/polarizabilities describes the solvent s ability to stabilize a charge or a dipole by virtue of its dielectric effect. The n values have been shown to be generally proportional to molecular dipole moments. The a scale of hydrogen bond donor acidities provides a measure of the solvent s ability to donate a proton. The jS scale of hydrogen bond acceptor basicities quantifies the solvent s ability to donate an electron pair (accept a proton). 

Kamlet MJ, Solomonovici A and Taft RW (1979) Linear solvation energy relationships, 5 correlations between infrared Av values and the scale of hydrogen-bond acceptor basicities. Journal of the American Chemical Society I0l 3734-3739. 

Kamlet, M.J., Gal, J.F., Maria, P.C. and Taft, R.W. (1985) Linear solvation energy relationships. Part 32. A coordinate covalency parameter, , which, in combination with the hydrogen bond acceptor basicity parameter,, permits correlation of many properties of neutral oxygen and nitrogen bases (including aqueous pa s). J. Chem. Soc., Perkin Trans. 2, 1583-1589. 

Taft, R.W., Gramstad, T. and Kamlet, M.J. (1982) Linear solvation energy relationships. 14. Additions to and correlations with the fi scale of hydrogen bond acceptor basicities. J. Org. Chem., 47, 4557-4563. 

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