Specific hydrogen bond interactions, 1,3-dipolar

Affinity chromatography involves precisely the same kind of electrostatic, hydrophobic, dipolar, and hydrogen-bonding interactions described above, but the specificity of binding is extraordinarily high. Demands on the homogeneity of the stationary phase and on the rigidity of the support are often... 

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. 

Since before the turn of the century it has been known that the optical activity of some chiral compounds is solvent dependent (1 ). For example, in 1877 Landolt (2) reported that the specific rotations of (+)-camphor, (-)-nicotine, (+)-diethyl tartrate, and (-)-turpentine varied with solvent and concentration. In the last decade there has been renewed interest in this solvent dependence. A number of different types of organic compounds has been investigated and the results have been interpreted in terms of variations in conformer populations that have resulted from either the effect of the dielectric on coulombic interactions between dipolar groups in the molecule (3), or from hydrogen-bond interactions between the solvent and the chiral solute (k). 

The simplicity of idealized electrostatic solvation models has led to the use of dielectric constant (e) and of the permanent dipole moment (p) as parameters of the so-called solvent polarity. However, the dielectric constant describes only the change in the electric field intensity that occurs between the plates of a condenser, when the latter is removed from vacuum and placed into a solvent. This induces a dipole moment in nonpolar solvent molecules and dipolar molecules are aligned. Hence, the dielectric constant describes only the ability of a solvent to separate electrical charges and orient its dipolar molecules. The intermolecular forces between solute and solvent molecules are, however, much more complicated in addition to the non-specific coulombic, directional, inductive and dispersion interactions, can also be present specific hydrogen bond, electron-pair donor (EPD)/electron-pair acceptor (EPA), and solvophobic interactions in solutions. 

These are defined as anionic dyes with substantivity for cellulosic fibres applied from an aqueous dyebath containing an electrolyte. The forces that operate between a direct dye and cellulose include hydrogen bonding, dipolar forces and non-specific hydrophobic interaction, depending on the chemical structure and polarity of the dye. Apparently multiple attachments are important, since linearity and coplanarity of molecular structure seem to be desirable features (section 3.2.1). The sorption process is reversible and numerous attempts have been made to minimise desorption by suitable aftertreatments (section 10.9.5). The two most significant non-textile outlets for direct dyes are the batchwise dyeing of leather and the continuous coloration of paper. 

Finally, some molecules possess permanent charge separations, or dipoles, such as are found in water. The general case for the interaction of any positive dipole with a negative dipole is called dipole-dipole interaction. Hydrogen bonding can be thought of as a specific type of dipole-dipole interaction. A dipolar molecule like ammonia, NH3, is able to dissolve other polar molecules, like water, due to dipole-dipole interactions. In the case of NaCl in water, the dipole-dipole interactions are so strong as to break the intermolecnlar forces within the molecular solid. 

Classification of Solvents in Terms of Specific Solute-Solvent Interactions Parker divided solvents into two groups according to their specific interactions with anions and cations, namely dipolar aprotic solvents and protic solvents (Parker, 1969). The distinction lies principally in the dipolarity of the solvent molecules and their ability to form hydrogen bonds. It appears appropriate to add to these two groups a third one, namely, the apolar aprotic solvents. 

N,N-Diethyl-4-nitroaniline, has an aromatic ring but no hydrogen bond donor substituent, shows a n-jt transition based on a non-specific interaction between ions. Dipolarity/polarizability, jz, is estimated by the solvatochromic shift of N,N-diethyl-4-nitroaniline using Eq. (3.3), where Amax is the absorption maximum for N, N-diethyl-4-nitroaniline. 

The immobilization of a large volume of liquid by a small quantity of gelator is achieved efficiently if the elementary assemblies are rodlike and have large aspect ratios. Such linear structures are determined by specific binding forces associated with the chemical constitution of the gelators. In nonaqueous liquids, the attractive forces are mainly the van der Waals type and can be supplemented by dipolar interactions, intermolecular hydrogen bonds, metal-coordination bonds, or electron transfers, etc. 

---