Dipole polarization

In this equation, AG°CS is taken to be negligible for p- and y-cyclodextrin systems and to be constant, if there is any, for the a-cyclodextrin system. The AG W term is virtually independent of the kind of guest molecules, though it is dependent on the size of the cyclodextrin cavity. The AG dw term is divided into two terms, AG°,ec and AGs°ter, which correspond to polar (dipole-dipole or dipole-induced dipole) interactions and London dispersion forces, respectively. The former is mainly governed by the electronic factor, the latter by the steric factor, of a guest molecule. Thus, Eq. 2 is converted to Eq. 3 for the complexation of a particular cyclodextrin with a homogeneous series of guest molecules ... 

Usually adsorption, i.e. binding of foreign particles to the surface of a solid body, is distinguished as physical and chemical the difference lying in the type of adsorbate - adsorbent interaction. Physical adsorption is assumed to be a surface binding caused by polarization dipole-dipole Van-der-Vaals interaction whereas chemical adsorption, as any chemical interaction, stems from covalent forces with plausible involvement of electrostatic interaction. In contrast to chemisorption in which, as it has been already mentioned, an absorbed particle and adsorbent itself become a unified quantum mechanical system, the physical absorption only leads to a weak perturbation of the lattice of a solid body. 

The polarity (dipole moment) of a molecule is the vector sum of the dipole moment of each individual polar bond. 

Technical 1,2, 5, 6, 9,10-HBCD is produced industrially by addition of bromine to cis-trans-trans-1,5,9-cyclododecatriene. This process leads theoretically to a mixture of 16 stereoisomers (six pairs of enantiomers and four mesoforms) and the product usually is a mixture of the three diastereoisomers a-, p- and y-isomer [14]. Normally, the y-isomer is the most dominant in the commercial mixtures (ranging between 75 and 89%), followed by a- and then p-isomer (10-13% and 1-12%, respectively) [15]. The dissimilarities in the structure of a-, p- and y-isomer might raise differences in polarity, dipole moment and in solubility in water. For example, the solubility of a-, p- and y-HBCD in water was 48.8,14.7, and 2.1 pg/L, respectively. Therefore, these different properties may explain the differences observed in their environmental behavior [16]. Covaci et al. [17] and Morris et al. [18] found that in sediments, the distribution of HBCD isomers was the same of... 

Generally, the solubihty characteristics of organic compounds depend on several properties of the participating components. For the solute, these properties are the molecular size and structure, polarity, dipole moment, va-por/sublimation pressure, and, in the case of a sohd solute, also its melting characteristics. When using SCCO2 as the solvent, mainly its dipole moment and quadrupole moment influence the solvatation process (Sect. 2.2). 

By appropriate choice of the type (or combination) of the organic solvent(s), selective polar dipole-dipole, proton-donor, or proton-acceptor interactions can be either enhanced or suppressed and the selectivity of separation adjusted [42]. Over a limited concentration range of methanol-water and acetonitrile-water mobile phases useful for gradient elution, semiempirical retention equation (Equation 5.7), originally introduced in thin-layer chromatography by Soczewinski and Wachtmeister [43], is used most frequently as the basis for calculations of gradient-elution data [4-11,29,30] ... 

Comparison of dipole moments shows only small differences in polarity. From these data, it can be reasoned that micellization in methanol is feasible. Dielectric constants and effective polarities (dipole moment/molar volume) support this premise with more divergent values. It is noted that bis(2-ethyIhexyI) sodium sulfosuccinate forms micelles readily in water and 2-octanol which have the highest and lowest dielectric constants, respectively, but micelles are formed only at low concentrations in methanol whose dielectric constant is intermediate in value. 

Each of the types of SPE sorbents discussed retains analytes through a primary mechanism, such as by van der Waals interactions, polar dipole-dipole forces, hydrogen bonding, or electrostatic forces. However, sorbents often exhibit retention by a secondary mechanism as well. Bonded silica ion-exchange sorbents primarily exhibit electrostatic interactions, but the analyte also experiences nonpolar interaction with the bonded ligand. Nonpolar bonded silicas primarily retain analytes by hydrophobic interactions but exhibit a dual-retention mechanism, due to the silica backbone and the presence of unreacted surface silanol groups [72], Recognition that a dual-... 

Polar/dipole-dipole Cyano, silica, alumina Florisil 1-10... 

Chemisorption systems are sometimes used for removing trace concentrations of contaminants, but the difficulty of regeneration makes such systems unsuitable for most process applications so most adsorption processes depend on physical adsorption. The forces of physical adsorption are weaker than the forces of chemisorption so the heats of physical adsorption are lower and the adsorbent is more easily regenerated. Several different types of force are involved. For nonpolar systems the major contribution is generally from dispersion-repulsion (van der Waals) forces, which are a fundamental property of all matter. When the surface is polar, depending on the nature of the sorbate molecule, there may also be important contributions from polarization, dipole, and quadmpole interactions. Selective adsorption of a polar species such as water or a quadrupolar species such as CO2 from a mixture with other nonpolar species can therefore be accomplished by using a polar adsorbent. Indeed, adjustment of surface polarity is one of the main ways of tailoring adsorbent selectivity. 

Force Ionic Polar (dipole-dipole) Dispersion... 

Potentially important discriminants of P450 selectivity include size (diameter), molecular mass or length of the molecule, planarity (aid1) or rectangularity (II w) of the molecule, lipophilicity (log P or log D 7.4), basicity/acidity of the compound (pAa), polarity (dipole moment) of the molecule, and compound lipophilicity for substrate binding to human P450s in drug metabolism. 

Practice Problem 13.1 1 State the bond type (polar or nonpolar) and the molecular polarity (dipole or no dipole) for each of the following substances (a) CI2 (b) NF3 (c) BrF (d) BCI3 (e) BeH2... 

Use the following terms to create a concept map valence electrons, nonpolar, covalent compounds, polar, dipoles, and Lewis structures. 

Electric polarization, dipole moments and other related physical quantities, such as multipole moments and polarizabilities, constitute another group of both local and molecular descriptors, which can be defined either in terms of classical physics or quantum mechanics. They encode information about the charge distribution in molecules [Bbttcher et al, 1973]. They are particularly important in modelling solvation properties of compounds which depend on solute/solvent interactions and in fact are frequently used to represent the -> dipolarity/polarizability term in - linear solvation energy relationships. Moreover, they can be used to model the polar interactions which contribute to the determination of the -> lipophilicity of compounds. 

Example Lewis structure H—Ci and polar (dipole) representation H Cl... 

It should be noted also that in principle the electronic polarization (dipole per unit length) is defined from the expectation value of x in the limit of a large system ... 

Stable Form Screening (slurries to identify stable polymorphs and solvates) Thermodynamics Targeted to find the most stable polymorph and stable solvates 10-20 solvents (neat or mixed) with variety in their properties and focus on those that provide high solubihty SolubUify, HBD/HBA propensity, polarity, dipole moment, dielectric constant... 

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