Robert W. Taft

Linear solvation energy relations

Solvents have been parameterized by scales of dipolarity/polarizability π*, hydrogen-bond donor (HBD) strength α, and hydrogen-bond acceptor strength β. Linear dependence (LSERs) on these solvent parameters are used to correlate and predict a wide variety of solvent effects, as well as to provide an analysis in terms of knowledge and theoretical concepts of molecular structural effects. Some recent applications utilizing this approach are presented. Included are analyses of solvent effects on (a) the free energies of transfer of tetraalkylammonium halide ion pairs and dissociated ions, (b) rates of nucleophilic substitution reactions, (c) the contrast in solvent effects of water (HBD) and dimethyl sulfoxide (non-HBD) on the acidities of m- and p-substituted phenols, (d) partition coefficients of non-HBD solutes between solvent bilayers, and (e) family relationships between proton transfer (and non-protonic Lewis acid) basicities and corresponding β values for monomer HBA. A comprehensive summary of LSER with references is given.

Solubility properties in polymers and biological media. 7. An analysis of toxicant properties that influence inhibition of bioluminescence in Photobacterium phosphoreum (the Microtox test).

Inhibition of bioluminescence in Photobacterium phosphoreum (the Microtox test) has been proposed as a cost-effective prescreening procedure to eliminate the relatively more innocuous chemicals from testing programs for toxicities of organic chemicals to fish. The biological response, as a function of toxicant properties, is given by log EC/sub 50/ (in ..mu..molL) = 7.61 - 4.11 anti V100 - 1.54 ..pi..* + 3.94..beta.. - 1.51..cap alpha../sub m/ n = 38, r = 0.987, SD = 0.28 where anti V is the solute molar volume and ..pi..*, ..beta.., and ..cap alpha../sub m/ are the solvatochromic parameters that measure dipolaritypolarizability, hydrogen-bond acceptor basicity, and hydrogen-bond donor acidity of the solute (toxicant). The above equation applies to compounds that act by a nonreactive toxicity mechanism, and it is suggested that for certain compounds, which are outliers relative to the above equation, reactive toxicity properties mask the effects of the nonreactive mechanism. The above equation is compared with a correlation of log EC/sub 50/ with octanolwater partition coefficients. 25 references, 2 figures, 2 tables.

Some observations regarding different retention properties of HPLC stationary phases

SummaryThe retention of 32 monocyclic aromatic compounds and 14 polynuclear aromatic hydrocarbons (PAHs) has been studied on four different bonded phases in each of two mobile phases. An additional data set of 21 monocyclic aromatics judiciously chosen for their well-established solvatochromic parameters, 12 PAHs and 12 polychlorinated biphenyls (containing up to 10 chlorines), were studied on a single column. The results indicate that despite the accuracy of the solvatochromic linear solvation energy method for predicting and correlating the octanol/water partition coefficients and water solubilities of these environmentally important materials, the methodology is limited to only certain types of bonded phases. As a corollary to this observation, we caution others that the common practice of estimating log Kow (Kow=octanol-water partition coefficient) based on measurement of the reversed-phase capacity factors should be limited to specific types of columns.

Linear solvation energy relationships. 44. Parameter estimation rules that allow accurate prediction of octanol/water partition coefficients and other solubility and toxicity properties of polychlorinated biphenyls and polycyclic aromatic hydrocarbons.

Methods are presented for estimation of V{sub I} (intrinsic molar volume), {pi}*, and {beta} of polychlorinated biphenyls and polycyclic aromatic hydrocarbons. Taken with the equation log K{sub OW} = 0.45 + 5.15V{sub I}/100-1.29 ({pi}* - 0.40{delta}) - 3.60{beta} reported recently by Leahy, these parameter estimation rules allow prediction of log K{sub OW} with a precision that is better than the usual reproducibility of the measurements between laboratories.

Linear solvation energy relationships. Part 3. Some reinterpretations of solvent effects based on correlations with solvent π* and α values

Solvent polarity and hydrogen bonding effects on a number of physical and chemical properties and reaction parameters are unravelled and rationalized by means of the solvatochromic comparison method and equations of the form XYZ=XYZ0+sπ*+aα, where π* is a measure of solvent polarity and α a measure of solvent hydrogen bond donor acidity. XYZs considered include ET values for eight electronic spectral transitions, two sets of nitrogen hyperfine splitting constants, a set of fluorescence lifetimes, logarithms of rate constants for four nucleophilic substitution reactions, and the ‘electrophilicity parameter,’E, of Koppel and Palm.

Linear solvation energy relationships Solvent effects on some fluorescence probes

Abstract Solvent effects on the fluorescence probes, 7-amino-4-methylcoumarin, 7-(N,N-dimethylamino)-4-methylcoumarin, and potassium 2-( p -toluidino)-6-naphthalenesulfonate are unravelled and rationalized in terms of multiple dependences on the solvatochromic parameters π * , α, and β.

Solubility properties in polymers and biological media. II. A new method for the characterisation of the adsorption of gases and vapours on solids.

Henrys constants at zero solute pressure have been determined by the gas chromatographic peak shape method for twenty-two solutes on four adsorbents (Rohm and Haas Ambersorb XE-348F carbonaceous adsorbent at 323 and 373 K, Sutcliffe Speakman 207A and 207C at 323 K, and Calgon Filtrasorb activated carbon at 323 K). The limiting values of log KH have been analysed in terms of solute dipolarity (pi 2*), solute hydrogen-bond acidity (alpha 2), and basicity (beta 2), and a new solute parameter (log L16), the solute Ostwald absorption coefficient on eta-hexadecane. The multiple linear regression equation, SP = SP0 + l.log L16 + s(pi 2* + d delta 2) + a alpha 2 + b beta 2 where in this instance SP = -log KH, can be used to identify the nature of the solute-adsorbent interactions, and to predict further values of log KH. For the solutes and solids we have studied, only the l.log L16 term is statistically significant, and hence--log KH is proportional to l.log L16. It is concluded that interactions between the gaseous solutes (that include alcohols and amines) and the four adsorbents involve just general dispersion forces.

Solute–solvent interactions in chemistry and biology. Part 7. An analysis of mobile phase effects on high pressure liquid chromatography capacity factors and relationships of the latter with octanol–water partition coefficients

log k′ values on a C18 stationary phase with 90/10, 75/25, 60/40, 45/55 and 30/70 methanol–water mobile phases are correlated in terms of the generalized linear solvation energy relationship, log k′= XYZo+mVI/100 +sπ*+bβm+aαm where VI is the intrinsic (van der Waals) molar volume, and π*, βm, and αm are the solvatochromic parameters that measure solute dipolarity–polarizability, hydrogen-bond acceptor basicity, and hydrogen-bond donor acidity. The correlation equations are combined with the corresponding equation for octanol–water partition coefficients to generate new equations that demonstrate the exact relationships between the various log ks and log Kow.

Linear solvation energy relationships. Part 37. An analysis of contributions of dipolarity–polarisability, nucleophilic assistance, electrophilic assistance, and cavity terms to solvent effects on t-butyl halide solvolysis rates

Solvolysis/dehydrohalogenation rates of t-butyl chloride in 21 hydrogen bond donor (HBD) and non-HBD solvents are well correlated (r= 0.9973, s.d. = 0.24) by the equation: log k=–14.60 + 0.48λH2/100 + 5.10π*+ 4.17α+ 0.73β where δH2 is the solvent cohesive energy density, and π*, α, and β are the solvatochromic parameters that scale solvent diplority–polarizability, HBD acidity (electrophilicity), and hydrogen-bond acceptor basicity (nucleophilicity). In the corresponding equation over the same solvent set for t-butyl bromide, the terms in δH2 and α are smaller still, and the terms in δH2 and β are not statistically significant. It is shown that a trifluoroethanol (TFE)–ethanol plot, wherein ButCl and 1-adamantyl chloride (1-AdCl) solvolysis rates are compared, can be interpreted as evidence for electrophilic assistance of 1-AdCl in TFE rather than the more usual interpretation of nucleophilic assistance to ButCl in EtOH–H2O.

Linear solvation energy relationships. 33. An analysis of the factors that influence adsorption of organic compounds on activated carbon

Abstract Adsorption coefficients on Pittsburgh CAL activated carbon, α ≡ lim c→o X C , where X is the amount adsorbed on carbon (mg/g) and C is the equilibrium concentration of the solute in aqueous solution (mg/1) are correlated by the equation, log α ga = −1.93 + 3.06 V /100 + 0.56π ∗ − 3.20β n = 37, r = 0.974, SD = 0.19 , where \ ga represents the infinite dilution partition coefficient between the adsorbed and solution phases, V is a measure of solute molar volume, and π ∗ and β are the solvatochromic parameters that scale dipolarity/polarizabilities and hydrogen bond acceptor basicities of the adsorbates. Defining an adsorbate/adsorbent interaction index by A x = α S w , where Sw, is the molar solubility of the adsorbate in water, and combining the above equation with a correlation equation for log Sw, leads to the following equation which is independent of the nature of the second phase. log A x = −1.50 − 0.15 V /100 + 1.04π ∗ + 2.06β n = 23, r = 0.887, SD = 0.11 . It is suggested that equations such as the above can serve to characterize the various types and grades of adsorbents.