Kamlet-Taft solvent property

Table 1. Absorption maxima of Neutral Red (NR) in various solvents and selective Kamlet-Taft solvent properties.

Kamlet-Taft solvent parameters Parameters of the Kamlet-Taft solvatochromic relationship that measure separately the hydrogen bond donor (a), hydrogen bond acceptor (P), and dipolarity/POLARiZABiLiTY (ji ) properties of solvents as contributing to overall solvent POLARITY. 

More recent solvatochromic studies [14-20] employ specialised dyes reflecting specific microscopic molecular interactions. For example, the Abboud-Kamlet-Taft solvent parameters [21-23] a, 3 and n give information on hydrogen bond donor and acceptor properties and the polarisability of a compound, respectively. For ionic liquids with [C4mim]-cations, the following order of [3- values was estab-... 

Kamlet-Taft Linear Solvation Energy Relationships. Most recent works on LSERs are based on a powerfiil predictive model, known as the Kamlet-Taft model (257), which has provided a framework for numerous studies into specific molecular thermodynamic properties of solvent—solute systems. This model is based on an equation having three conceptually expHcit terms (258). 

H-bonding is an important, but not the sole, interatomic interaction. Thus, total energy is usually calculated as the sum of steric, electrostatic, H-bonding and other components of interatomic interactions. A similar situation holds with QSAR studies of any property (activity) where H-bond parameters are used in combination with other descriptors. For example, five molecular descriptors are applied in the solvation equation of Kamlet-Taft-Abraham excess of molecular refraction (Rj), which models dispersion force interactions arising from the polarizability of n- and n-electrons the solute polarity/polarizability (ir ) due to solute-solvent interactions between bond dipoles and induced dipoles overall or summation H-bond acidity (2a ) overall or summation H-bond basicity (2(3 ) and McGowan volume (VJ [53] ... 

From a practical viewpoint, Ej values are quickly and easily obtained, giving a very useful and convenient scale. However, a general polarity scale based on a single probe molecule has its limitations because a single compound cannot experience the diversity of interactions that the whole range of solvents can offer. The Kamlet-Taft parameters a, /3 and n tackle this problem by using a series of seven dyes to produce a scale for specific and nonspecific polarity of liquids [23], Whilst it undoubtedly gives a more detailed description of the solvents properties,... 

Hydrogen bond donor solvents are simply those containing a hydrogen atom bound to an electronegative atom. These are often referred to as protic solvents, and the class includes water, carboxylic acids, alcohols and amines. For chemical reactions that involve the use of easily hydrolysed or solvolysed compounds, such as AICI3, it is important to avoid protic solvents. Hydrogen bond acceptors are solvents that have a lone pair available for donation, and include acetonitrile, pyridine and acetone. Kamlet-Taft a and ft parameters are solvatochromic measurements of the HBD and HBA properties of solvents, i.e. acidity and basicity, respectively [24], These measurements use the solvatochromic probe molecules V, V-die lliy I -4-n i in tan iline, which acts as a HBA, and 4-nitroaniline, which is a HBA and a HBD (Figure 1.17). 

The study of solute-solvent and solvent-solvent interactions in mixed solvents has been gaining significance in recent years61-64, because of the increasing application of these solvents. Casassas and collaborators67 have used the Kamlet-Taft multiparametric equation for the correlation of dissociation constants of acids in 1, 4-dioxane-water mixtures. They found that when the main solvent is retained the property does not involve significant changes in the cavity volumes and, in those cases, the pK in binary solvents can be described by equation 8 ... 

The QSAR technique, widely developed by Kamlet, Taft and coworkers38,98 for the prediction of specific solute-solvent interactions, has been used to predict the different solute-solvent contributions to property variations of compounds. The influence of solvent on the relative basicity of dipolar trimethylamines has been recently studied a descriptor was developed to describe a unique solute-solvent interaction involving dipolar amines99. 

Investigation of stable simple enols has recently been undertaken with a series of p,P-dimesityl-a-ethenols [29] and [30] in which Mes = 2,4,6-tri-methylphenyl. In this work, 5(OH) and /hcoh were measured for a series of compounds with various a-substituents and in a range of solvents (Biali and Rappoport, 1984 Rappoport et al., 1988). The nmr parameters were shown to be linearly related to the Kamlet and Taft P-variable, a solvent property that is related to its ability to act as a hydrogen-bond acceptor (Kamlet and Taft, 1976 Taft et al., 1985). 

Baker, S.N., Baker, G.A., Bright, F.V., Temperature-dependent microscopic solvent properties of dry and wet l-butyl-3-methylimidazolium hexafluo-rophosphate Correlation with ET(30) and Kamlet-Taft polarity scales. Green Chem., 4,165-169, 2002. 

A number of studies have attempted to characterize ionic liquids through their dielectric constant, and all have observed inconsistencies between the measured dielectric constant and the solvation properties of the liquid. Recent experiments making use of dielectric reflectance spectroscopy [214] indicate dielectric constants in the range of 10-15 for a series of imidazolium-based ILs, substantially lower than those for molecular solvents observed to possess comparable polarities as estimated by solvatochromism. Weingartner [215] has recently published a series of static dielectric constants obtained from dielectric reflectance spectroscopy, and compared them with those of common molecular liquids. The analysis includes comparison with the Kamlet-Taft ji parameter for the liquids from Eq. (11) we have prepared a plot of n versus dielectric constant in Fig. 6. The relationship between n and e for molecular liquids... 

On the basis of such a classification an empirical approach based on the so-called solvent empirical parameters was formulated to evaluate solvent effects on nuclear shieldings. In brief, this approach, originally proposed by Kamlet, Taft and co-workers [20] for electronic excitations, does not involve QM or other types of calculations but introduces a numerical treatment of experimental data obtained for a given reference system to obtain an estimate of solvent effects on various properties. 

Kamlet, Taft, Abraham et al. have further modified Eq. (7-54) in order to correlate the solubility and distribution behaviour of nonelectrolyte solutes with solvent properties, according to Eq. (7-56) [271, 272],... 

Dealing with this type of multiparameter correlation analysis, a series of twelve articles entitled Solubility Properties in Polymers and Biological Media was published by Kamlet, Taft, Abraham et al. (Part 1 [273]...Part 12 [274]), as well as another series entitled Solute Solvent Interactions in Chemical and Biological Systems (Part 4 [358]... Part 7 [359]). The application of the LSER equation (7-58) to the prediction of solubilities of organic nonelectrolytes in water, blood, and other body tissues has been reviewed [286],... 

There is also, as expected, a correlation between the formal potentials of various systems with DN or the Kamlet-Taft, Lewis basicity parameter [84] shown in other papers (see for instance [85]). Also, in this case, with increasing donor properties of the solvents, the formal potential is moving to more negative values expressed versus a solvent-independent reference electrode, the Foe /Foe system. 

Kamlet-Taft parameters have also been obtained for some perfluorinated solvents.They are not hydrogen bond donors (a is typically 0.0) and are typically extremely poor hydrogen bond acceptors ( 3 is small and negative). They are extremely difficult to polarize, and this leads to a strongly negative tt parameter. This last property explains why they typically form biphasic systems with organic solvents. 

The relative strength of the hydrogen-bonding interactions may also be estimated indirectly by correlating their effect on the optical transition frequencies of the chromophore. In the Kamlet-Taft (K-T) analysis , any solvent-influenced property of the solute... 

Over the last few years, the development of solvents of desired properties with a particular use in mind has been challenging. To evaluate the behaviour of a liquid as solvent, it is necessary to understand the solvation interactions at molecular level. In this vein, it is of interest to quantify its most relevant molecular-microscopic solvent properties, which determine how it will interact with potential solutes. An appropriate method to study solute-solvent interactions is the use of solvatochromic indicators that reflect the specific and non-specific solute-solvent interactions on the UV-Vis spectral band shifts. In this sense, a number of empirical solvatochromic parameters have been proposed to quantify molecular-microscopic solvent properties. In most cases, only one indicator is used to build the respective scale. Among these, the E (30) parameter proposed by Dimroth and Reichardt [23] to measure solvent dipolarity/polarisability which is also sensitive to the solvent s hydrogen-bond donor capability. On the other hand, the n, a and P (Kamlet, Abboud and Taft)... 

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