Solvents hydrogen bond donor

The .p(30) scale of solvent polarity is sensitive to both solvent dipolarity and polarizability, as well as the solvent hydrogen-bond donor ability. 

Taft RW, Kamlet MJ (1976) The solvatochromic comparison method. 2. The a-scale of solvent hydrogen-bond donor (HBD) acidities. J Am Chem Soc 98 2886-2894. 

The solvatochromism of [Fe(phen)2(CN)2] and [Fe(phen)2(CN)2] has been discussed, with particular reference to solvent hydrogen-bond donor properties. Various solvation models have been applied to solvatochromism of [Fe(diimine)2(CN)2], and cormections between solvatochromism, electronic absorption spectra, and color perception parameters discussed in relation to [Fe(phen)2(CN)2]. Solvatochromic properties have been documented for [Fe(bipy)2(CN)2]>... 

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). 

The term hydrogen-bond acceptor (HBA) refers to the acceptance of the proton of a hydrogen-bond. Therefore, HBA solvents are also electron-pair donor (EPD) solvents. Hydrogen-bond donor (HBD) refers to the donation of the proton. Therefore, HBD solvents behave as protic solvents. 

Taft, R.W. and Kamlet, MJ. (1976). TTie Solvatochromic Comparison Method. 2. The a-Scale of Solvent Hydrogen-Bond Donor (HBD) Acidities. J.Am.Chem.Soc., 98, 2886-2894. 

Taft, R.W. and Kamlet, M.J. (1979) Linear solvation energy relationships. Part 4. Correlations with and limitations of the a scale of solvent hydrogen bond donor acidities./. Chem. Soc. Perkin Trans. 2, 1723-1729. 

To investigate the possibility of variable ESA, we have used the solvatochromic method of Kamlet and co-workers (7-10). According to this approach, a solvent-dependent phenomenon (in this case log solvolysis rate k) is a function of four solvent properties solvent hydrogen-bond donor ability or electrophilicity, a solvent hydrogen-bond acceptor ability or nu-... 

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). 

The following treatment is based on the use of three different scales [i.e., (S), g2(S), and g3(S)] which have been determined empirically the polarity scale 7T, the a scale of solvent hydrogen bond donor (HBD) acidities (71), and the /3 scale of solvent hydrogen bond acceptor (HBA) basicities (72). To avoid possible pitfalls resulting from experimental errors or from specific solvent effects, the solvatochromic parameters have been arrived at by averaging multiple, s determined for each solvent with a variety of different indicators. Quite generally, the purpose of this study is the systematic correlation of solvent effects on diverse properties and reactivity parameters, XYZ, by means of expressions of the type. 

The appreciable a/s ratio in Equation 110 indicates that the t-(30) scale, usually considered to be a generalized measure of solvent polarity, is for protic solvents at least as much a measure of solvent hydrogen bond donor ability. On reviewing the literature on correlations with the t-(30) solvent polarity scale in light of Equation 110, it becomes evident that the best linear Hts have been with properties that coincidentally have had a/s ratios near that for 47. Thus, the widespread acceptance of the t-(30) scale has resulted in part from... 

Kamlet MJ, Taft RW. The solvatochromic comparison method. I. The.beta.-scale of solvent hydrogen-bond acceptor (HBA) basicities. J Am Chem Soc. 1976 98 377-383. Taft RW, Kamlet MJ. The solvatochromic comparison method. 2. The.alpha.-scale of solvent hydrogen-bond donor (HBD) acidities. J Am Chem Soc. 1976 98 2886-2894. Yokoyama T, Taft RW, Kamlet MJ. The solvatochromic comparison method. 3. Hydrogen bonding by some 2-nitroaniline derivatives. J Am Chem Soc. 1976 98 3233-3237. 

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