Polar molecule interaction

Closely related to the London interaction is the dipole-induced-dipole interaction, in which a polar molecule interacts with a nonpolar molecule (for example, when oxygen dissolves in water). Like the London interaction, the dipole—induced-dipole interaction arises from the ability of one molecule to induce a dipole moment in the other. However, in this case, the molecule that induces the dipole moment has a permanent dipole moment. The potential energy of the interaction is... 

For the case of a polar molecule interacting with a nonpolar molecule, an induction energy term should be considered see Section 13.5 of [178]. This additional interaction modifies the interaction parameters as... 

Highly polar molecules, such as HC146 and NH334 have very large mixing cross sections, as shown by Stebbings et al. It is not clear whether the polar molecules interact with only the electron of the Rydberg atom or with the atom as a whole. 

All molecules, including polar molecules, interact by the London mechanism. However, if the molecules are polar, they may also interact by the dipole-dipole mechanism. The latter is particularly important when the molecules are in a condensed phase and do not rotate freely (the interaction then has a longer range because it varies as 1/r3 rather... 

Because the polar molecules interact with other molecules in the material, they transfer their motion, which has been imparted to them from the electric field, to the entire sample as heat. 

We consider the so-called Langevin model for ion-molecule reactions. An ion and a neutral non-polar molecule interact—at large distances—through an ion-induced-dipole potential... 

When a polar molecule and a non-polar molecule approach each other, the electric field of the polar molecule distorts the electron charge distribution of the non-polar molecule and produces an induced dipole moment within it. The interaction of the permanent and induced dipoles then results in an attractive force. This induction contribution to the electrostatic energy is always present when two polar molecules interact with each other. 

The field dipole energy appears in the instance of polar molecules interacting with an adsorbent that have a crystalline electric field. Subsequently, for polar molecules, the field dipole term could be written as follows... 

As we ve seen, polar molecules interact with each other somewhat as bar magnets do, and the interaction is termed a dipole interaction. In a dipole interaction, the positive end of one polar molecule lines up with the negative end of another, as the north pole of one bar magnet will line up with the south pole of another—but these magnets are rotating, vibrating, and flying in all directions. 

When a dipolar and a non-polar molecule interact, as shown in Figure 2.6 b, the polarizing held arises from the permanent dipole and not from an ion. As a result, the applied electrical held is weaker than the interactions between ions and non-polar molecules. The magnitude of this electric held can be calculated for a hxed dipole, p, oriented at an angle, 0, to the line joining it to the polarizable molecule,... 

Polar molecules interact more strongly at large distances than do nonpolar molecules, and generally form nonideal solutions. One model for solution nonidealities in a binary mixture consisting of a nonpolar species, which we denote by A, and a polar substance, designated by the symbol B, is based on the supposition that the polar substance partially dimerizes,... 

Solvation plays a key role because the magnitude of the electrostatic ion-polar molecule interaction is large, say 10-20 kcal mol , comparable to the barriers for concerted bond-switching reactions. Consider the Sn2 reaction OH + CH3CI Cl -h CH3OH in the gas phase. The reaction is concerted so the new (CH3-OH) bond forms as the old (CH3-CI) bond is stretched. This process has an activation barrier but it must be significantly lower than the energy needed to break the old bond. On the other hand, as the reactants approach, the first interaction they experience... 

Theoretical treatment of the solvation of ions is quite difficult. If we could use a simple electrostatic approach in which polar molecules interact with a charged ion, the problem would be much simpler. However, the fact that the polar solvent molecules interact with an ion causes their... 

Whether or not a molecule is polar is important because polar molecules tend to behave differently than nonpolar molecules. Water and oil do not mix, for example, because water molecules are polar and the molecules that compose oil are generally nonpolar. Polar molecules interact strongly with other polar molecules because the positive end of one molecule is attracted to the negative end of another, just as the south pole of a magnet is attracted to the north pole of another... 

Apolar molecules interact by means of dispersion forces, which are always attractive independently of their relative orientation, and for this reason they display little tendency to give a long-range ordered molecular arrangement in condensed phases. On the other hand, polar molecules interact also by means of dipole-dipole interactions, which are attractive or repulsive depending on the relative orientation of the molecules. It follows that these molecules display a more marked tendency to give a three-dimensionally unlimited ordered molecular arrangement. In the case of amphiphilic molecules, characterized by the coexistence of spatially separated apolar (alkyl chains) and polar moieties, both these parts... 

Finally, there seems to be a consensus about the concepts of polar and nonpolar liquids. Water is a polar liquid and mixes readily with other polar liquids, i.e., liquids consisting of polar molecules, like alcohol, at least as long as the sizes of the molecules are not too different, whereas it is insoluble in nonpolar liquids like benzene. If in liquid form, constituent polar molecules interact strongly with other polar molecules and, in particular, are easily oriented in external fields. We will also use this criterion for a liquid crystal. That is, we will call a liquid crystal polar if it contains local dipoles that are easily oriented in an applied electric field. 

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