Electrostatic dipole interactions orientational ordering

In this case, a detailed structural investigation was possible because of the high degree of orientational order. It is believed that this order results from an electrostatic interaction between the electron-rich hexagon of the C60 andthe dipole formed by the C-H bonds of the solvent placed near the equator of the C60 molecule. Therefore, there remains a possibility that such interactions also affect the distortion, which might not represent the purely intrinsic JTD. 

The ordering of liquids can be promoted by attractive interactions between an ion and a polar molecule. For example, electrostatic interactions between a positively charged ion (cation) and a water molecule will occur readily in an aqueous environment. This ion-dipole interaction involves the orientation of the partially localized negative charge of the water molecule toward the positively charged cation, forming a solvation shell (hydration shell in the case of water). At close separations, two solvated particles will be repelled from one another due to the bound water molecules that form the hydration layer around the cation. This hydration force is particularly important for ions or molecules in solution as it minimizes their direct contact due to the van der Waals attraction, controlling the stability of the solution. 

These endo-exo preferences are energetically small and are of the order of a kcal mol-1. Consequently, factors such as dipole-dipole,27 electrostatic,28 steric29 and solvent effects27,30 can also influence the stereoselectivity. Secondary orbital interactions may not provide all of the answers, but no other theory can rationalize both the preferential endo orientation of 4 + 2 and 8 + 2 cycloadditions and the exo orientation of 6 + 4 cycloadditions so efficiently. See also Exercise 12. 

In order to understand the overall orientation of the chromophores within guest-host systems under differing external electric fields, we examine the orientational alignment of the dipole moment of the chromophores with respect to the direction of the external electric field. In the non-interacting rigid gas model, the intermolecular electrostatic interactions are ignored and one can describe a general order parameter of... 

In order to account for the attraction between non-polar molecules on the basis of the electrostatic theory, it is necessary to regard the molecule as a quadrupole, which may be pictured as a molecule with two identical dipoles directed in opposite directions. The quadrupole may be either linear or rectangular as depicted in Figure 39. Such a treatment may be applied not only to molecules such as COs, which consist of two identical polar bonds pointing in opposite directions, but also to homopolar molecules such as H2. It is possible to calculate the field due to the quadrupole and to consider, in a way similar to that described above, two types of interaction, mutual orientation of the quadrupoles and polarization of one molecule in the field of another. The calculation shows that the field due to the quadrupole decreases more rapidly with the distance from the molecule than does the field due to the dipole. The attractive force is thus a short range force which rapidly falls to zero as the distance from the molecule is increased. 

Helices that form pores will be amphiphilic because it is more favorable to have situated in the inner side of the pore hydrophilic amino acid side chains, while the outer side of the pore represents a more favorable environment for hydrophobic amino acid side chains since these are in contact with lipids. Some authors point to the possibility that such a structure contains hydrogen bonds between amino acid residues and the main chain in order to compensate opposite charges and oppositely oriented dipoles. A comparison between the strength of different interactions in the structure of soluble and membrane proteins leads to the conclusion that because of the decreased strength of hydrophobic interactions and increased strength of electrostatic interactions (because of the reduced dielectric constant), the electrostatic interactions play the main role in stabilizing the structure of membrane proteins. ... 

Despite its Httle practical use, some qualitative conclusions can be drawn from Eq. (1). First, there can be large long-range contributions to the interaction, in particular if the adsorbed species possesses low order multipole moments, such as a charge (1a=0) or a dipole moment (1 =1). Asymptotically, the term with the lowest multipole moment will prevail, but at shorter separations other contributions might be more important Second, the electrostatic interaction can be both repulsive or attractive, depending on the sign of the multipole moments and on the orientation of the molecule relative to the surface. 

A pioneer effort to the account for electrostatic interaction effects in dipole reorientations and correlation functions was made by Brot and Darmon (39) in their Monte Carlo simulations for the partially ordered solid phase of 1 2 3 trichloro 4 5 6 trimethyl benzene (TCTMB) using the point charge model already mentioned in 2.4. Calculations of transition rates between 6 fold rotational wells of fluctuating depth as a result of changing neighbor orientations resulted in essentially Debye relaxation at 300 Kt but a second simulation at 186 K for which considerable rotational ordering is present produced very nearly a circular arc with od = 0.28 as compared to the experimental Ad = 0.39. 

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