Solvents dipole moment

It was found that a better representation of non-specific interactions between solvents and the monosubstituted dipolar trimethylammonium ions is gained from the product of tt and the solvent dipole moment (/x). The obtained results were compared with the gas-phase basicity and the solvent attenuation factors (SAF) were calculated". 

The influence of the polarity of solvents on their ability to dissolve nitrocellulose has been also demonstrated by Wo. Ostwald [50], who has introduced the value fi2/e as an expression characterizing the strength of solvent ( —dipole moment, e-dielectric constant). Good solvents of acetyl celluloses are characterized by a high iM2/s value. The physical significance of /i2/e is not clear, however, and its introduction has not helped to clarify the process of dissolution. 

The rates of Diels-Alder reactions are little affected by the polarity of the solvent. If a zwitterionic intermediate were involved, the intermediate would be more polar than either of the starting materials, and polar solvents would solvate it more thoroughly. Typically, a large change of solvent dipole moment, from 2.3 to 39, causes an increase in rate by a factor of only 10. In contrast, stepwise ionic cycloadditions take place with increases in rate of several orders of magnitude in polar solvents. This single piece of evidence rules out stepwise ionic pathways for most Diels-Alder reactions, and the only stepwise mechanism left is that involving a diradical. 

While the clathrate model is attractive, it is not correct to assume that the water is organized in some long-lived structure the observation that the self-diffusion coefficient for co-sphere water is larger than that for the solute rules this out. However, the rotational correlation time is shorter for ethanol and t-butyl alcohol in water (in the clathrate cage ) than in the pure liquid (Goldammer and Hertz, 1970 Goldammer and Zeidler, 1969). Nmr experiments show that in water the solvent dipole moments point away from the apolar groups (Hertz and Radle, 1973). 

According to its and NMR spectra, this vinylogous amide exists as the E-s-E form in polar solvents such as [D4]methanol, and as a mixture of Z-s-Z and E-s-E isomers in nonpolar solvents such as deuterio-trichloromethane (30 cmol/mol /36a) and 70 cmol/mol (36b)). As expected, the more dipolar E-s-E form is stabilized in polar solvents (dipole moment of the related E-s-E 3-dimethylaminopropenal 21 10 Cm). 

The solvatochromic polarity parameter Px(30) or Pj is also related to some physical solvent properties beyond the solvent dipole moment, provided that solvents capable of specific solute/solvent interactions are excluded. In particular, Bekarek et al. 

It has been stated that, when specific hydrogen-bonding effects are excluded, and differential polarizability effects are similar or minimized, the solvent polarity scales derived from UV/Vis absorption spectra Z,S,Ei 2Qi),n, Xk E- ), fluorescence speetra Py), infrared spectra (G), ESR spectra [a( " N)], NMR spectra (P), and NMR spectra AN) are linear with each other for a set of select solvents, i.e. non-HBD aliphatic solvents with a single dominant group dipole [263]. This result can be taken as confirmation that all these solvent scales do in fact describe intrinsic solvent properties and that they are to a great extent independent of the experimental methods and indicators used in their measurement [263], That these empirical solvent parameters correlate linearly with solvent dipole moments and functions of the relative permittivities (either alone or in combination with refractive index functions) indicates that they are a measure of the solvent dipolarity and polarizability, provided that specific solute/ solvent interactions are excluded. 

As discussed, the solvent dipole moments, concentration, and temperature play a significant role in determining the structure of cinchona alkaloids and their derivatives in solution. In order to delineate the intimate details of the mechanism of action of cinchona alkaloids and their derivatives, a thorough understanding of their real structure in solution is needed. Furthermore, such detailed information on the real structure in solution would make it possible to develop new and more powerful chiral catalysts and discriminators. 

Solvent Dipole moment (h) Dielectric constant ( ) LogP Hildebrand solubility factor ( )... 

Solvent Dipole Moment p/debye Polarizability 10 /nm Diameter o/nm Lennard-Jones Energy Elj b /K... 

Ref. (2)]. While a dependence of e" on solvent dipole moment or dielectric constant has been refuted for numerous experimental adsorption systems [c.g.. Ref. (7)], the belief that dielectric constant defines both solvent strength and sample adsorption energy continues to find support by many workers. The dependence of e values on solvent dielectric constant is tested in Fig. 8-13 for adsorption on alumina. There is a tendency for solvent strength to follow solvent dielectric constant, but the exceptions to this relationship are both numerous and large (e.g., dioxane, e = 0.56 and dielectric constant = 2.2, versus methylene chloride, e = 0.42 and dielectric constant = 9.1). Consequently, the dielectric constant of the solvent is quite limited in its ability to predict solvent strength. The data of Fig. 8-13 do not support any fundamental relationship between solvent strength and dielectric constant. 

The material presented in the chapter illustrates the difficulties connected with experimental determination and theoretical computation of dipole moments in general and heterocyclic compounds in particular. It is obvious that more work is needed on solute-solvent interactions, role of the polarity of the solvent, dipole moments in solution v. dipole moments in the gas phase, dielectric constant measurements V5. microwave spectroscopic data, improvements in calculations, better solvatochromic equations, etc. 

On heating, the cis isomer begins to decompose at 224°, whereas the trans isomer does not begin to decompose until 256°. In phenol solution, the freezing-point depression shows that both isomers are monomolecular. Because of the limited solubility of both isomers in nonpolar solvents, dipole moments have not been determined. ... 

Figure 11 Left panel Fi(X) (1) and T (7<) (2) from the analytical Q model (dashed lines) and from simulations (dash-dotted lines) at tnoi/m — 2 and moi/tn — 10 in the dipolar lattice with Pzm2/ct3 = 1.0 Ro/o = 0.9 a is the hard-sphere diameter of the solvent molecules m is the solvent dipole moment. The dashed and dash-dotted curves essentially superimpose. Right panel 1/oq versus Circles indicate the lattice...

Coulomb forces are responsible for the stability of ionic crystals (e.g., NaCl). When such a compound is dissolved in a polar solvent (dipole moment //), dissociation and simultaneous solvation of the ions occur. The force of attraction between the ions is now inversely proportional to the dielectric constant of the solvent, and is thus reduced. New ion dipole forces are formed as a result of the attraction of the permanent dipoles of the solvent by the ions ... 

Analysis of solvent shifts requires a knowledge of the transition concerned, and how this changes the dipole moment of the absorbing species. In interpreting observed shifts it is necessary to distinguish between polarisation red shifts (proportional to solvent refractive index), and shifts dominated by solvent cage strain, when solvent dipole moment may be more important. Nevertheless, in many cases the use of a simplified, approximate treatment yields useful information about both the ground and excited states. Examples of solvent shifts are included in the discussion of Types of Transition (sect. 4.4) and in Selected Applications (sect. 4.6). 

Table 7.6 Three properties of organic solvents dipole moments, fi (debye, ID = 10 esu...

It is, of course, natural from many points of view that aqueous solutions have been in the foreground for studies of electrolyte solutions, while studies of halide ion quadrupole relaxation in non-aque-ous solvents are quite few. However, studies of non-aqueous and mixed solvent systems are in certain respects highly relevant. For example, in order to test relaxation theories the possibility of making marked changes in solvent dipole moment, molecular size, dielectric constant, solvation number etc. should be very helpful. Also, the elucidation of certain general aspects of interactions and particle distributions in electrolyte solutions may be more easily achieved for non-aqueous systems. One such point is ion-pair formation, which for simple salts is not of great importance in water. Finally, of course, the quadrupole relaxation method may, as for aqueous solutions, be applied to more special problems such as ion solvation, complex formation etc. In studies of preferential solvation phenomena disorder effects in the first sphere may in certain cases be expected to lead to dramatic changes in the quadrupole relaxation rate. 

Solvent Dipole moment [15] p (D) Polarity [18] t3o (kcal moF ) Number of hydrogen bond donor atoms per molecule Number density Up (cm )... 

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