Dipole-ion interactions

Ion-dipole interaction is a weaker electrostatic interaction compared to ion-ion interaction. Energy of such interaction varies in accordance to Equation 2.9  

It is evident from Equation 2.10 that whether E is positive or negative depends on the magnitude of 9. In view of the set criteria based on which Equation 2.9 has been derived, the positive pole of the dipole will be nearer to the positive point charge ej when 9 90° and 9 270°, and the negative pole of the dipole will be nearer to the positive point charge ej when 9 90° and 9 270°. 

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The favorability of acid-base reactions is affected, in pa by electrostatic interactions between charged atoms a dipoles within the same molecule. The equilibrium w shift in the direction of an ion that is stabilized 1 intramolecular ion-dipole interactions. 

Decide if ion-dipole interactions are responsible for the observed substituent effects. Obtain the charge on carbon and nitrogen in each cyano group. What evidence is there for a polar CN bond Should the ion (O )-dipole (CN) interaction be stabilizing or destabilizing Can these interactions explain the trends in electrostatic potential (Hint Focus on changes in O—CN distance and in orientation of the cyano group.)... 

Ion-dipole interactions interact over longer distances. Their mean interaction energy 0id decreases with r-4 3) ... 

In this review, recent development of active transport of ions accross the liquid membranes using the synthetic ionophores such as crown ethers and other acyclic ligands, which selectively complex with cations based on the ion-dipole interaction, was surveyed,... 

Ionophores constitute a large collection of structurally diverse substances that share the ability to complex cations and to assist in the translocation of cations through a lipophilic interface.1 Using numerous Lewis-basic heteroatoms, an ionophore organizes itself around a cationic species such as an inorganic metal ion. This arrangement maximizes favorable ion-dipole interactions, while simultaneously exposing a relatively hydrophobic (lipophilic) exterior. 

Exercise 3.5. Consider the simple case of a positive ion surrounded by 10 dipoles, using for the dipole-dipole interaction the potential of Exercise 3.3 and for the ion-dipole interaction the potential... 

Ion-dipole interactions are strong for small, highly charged ions one consequence is that small, highly charged cations are often hydrated in compounds. 

O I Predict the relative strengths of ion-dipole interactions (Section 5.2). 

Examples Al3+ S()42. See also anion cation. ion-dipole interaction The attraction between an ion and the opposite partial charge of the electric dipole of a polar molecule. 

LL is smaller than KH. so it has stronger ion-dipole interactions with I LO than K+, which will make it move more slowly than I[Pg.1012]

Water is highly polar, but it is not ionic. How, then, can water act as a solvent for ionic solids A salt dissolves only if the interactions between the ions and the solvent are strong enough to overcome the attractive forces that hold ions in the ciystal lattice. When an ionic solid forms an aqueous solution, the cations and anions are solvated by strong ion-dipole interactions with water molecules. 

The third step is solvation of the ions by solvent molecules. Water molecules cluster around each ion, oriented to give attractive ion-dipole interactions. This step releases energy. Although each individual ion-dipole interaction is weak, each ion forms from four to eight such interactions, depending on the size of the ion and the concentration and temperature of the solution. Taken together, the vast number of ion-dipole interactions results in a substantial release of energy. 

Solvated ions have a complicated structure. The solvent molecules nearest to the ion form the primary, or nearest, solvation sheath (Fig. 7.2). Owing to the small distances, ion-dipole interaction in this sheath is strong and the sheath is stable. It is unaffected by thermal motion of the ion or solvent molecules, and when an ion moves it carries along its entire primary shell. In the secondary, or farther shells, interactions are weaker one notices an orientation of the solvent molecules under the effect of the ion. The disturbance among the solvent molecules caused by the ions becomes weaker with increasing distance and with increasing temperature. 

The surface potential of a solution can be calculated, according to Eq. (10.18), from the dilference between the experimental real energy of solvation of one of the ions and the chemical energy of solvation of the same ion calculated from the theory of ion-dipole interaction. Such calculations lead to a value of -1-0.13 V for the surface potential of water. The positive sign indicates that in the surface layer, the water molecules are oriented with their negative ends away from the bulk. 

AOT is an anionic surfactant complexed to the counterion, usually sodium. The water molecules in the intramicellar water pool are either free or bound to the interface. The bound water can interact with various parts of the surfactant. These interactions include hydrogen-bonding interactions with oxygen molecules on the sulfonate and succinate groups, ion-dipole interactions with the anionic surfactant headgroup and counterion, dipole-dipole interactions with the succinate group, and dispersive forces with the hydrocarbon tails. 

The expression for the ion-dipole interaction energy Uid is obtained analogously as the sum of the energies of coulombic interaction of an ion (charge q) with charges q and —q on the ends of the dipole, i.e. 

Surface active agents, more commonly known as surfactants, are the groups of chemical compounds that in the most common form constitute an ionic or polar portion (hydrophilic head) and a hydrocarbon portion (hydrophobic tail). The ionic or polar portion interacts strongly with the water via dipole-dipole or ion-dipole interactions and... 

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