Atomic dipolar polarizations

The total dipole moment of a molecule is the resultant of the vector sum of the atomic dipolar polarization ( a.lp) of all the atoms in the molecule and of all the charge transfer dipoles arising from the transfer of charge between bonded... 

It is important to understand that the atomic charges refer to atoms that are not spherical. Consequently the centroid of electronic charge of an atom does not in general coincide with the nucleus, and each atom therefore has an electric dipole moment—or, more generally, an electric dipolar polarization (since only the dipole moment of electrically neutral atoms is origin independent). 

The heating effect relies upon dielectric polarization [1], itself containing components of electronic, atomic, dipolar, and interfacial polarization, of which the last two have timescales which allow them to contribute to the overall heating effect at these frequencies. The loss tangent, tan 5, consists of two components, s, the dielectric constant, and s", the dielectric loss, where... 

The first moment provides a measure of the extent and direction of the dipolar polarization of the atom s charge density by determining the displacement of the atom s centroid of negative charge from the position of its nucleus. The dipole moment of a neutral molecule is expressed as... 

Unlike the polarization of the base atom in a regular hydrogen bond interaction, the dipolar polarization of a noble gas atom is towards the hydrogen. In the relatively weak complex of HF with N2, the change in the polarization of the base N away from H is very small. This interaction is transitional between the two patterns of atomic polarizations that result from the mutual penetration of closed-shell systems with little or no accompanying charge transfer, the features common to van der Waals and hydrogen-bonded interactions. 

Insulator and capacitor applications depend on the dielectric properties of ceramics, that is, on their polarization response to an applied electric field. The four polarization mechanisms which describe the displacement of charged species in ceramics are (1) electronic polarization—the shift of the valence electron cloud with respect to the nucleus (2) ionic or atomic polarization— movement of cation and anion species (3) dipolar polarization—perturbation of the thermal motion of ionic or molecular dipoles and (4) interfacial polarization—inhibition of charge migration by a physical barrier. Further discussion of polarization phenomena may be found in Reference 1. 

So-called atomic polarization arises from small displacements of atoms under the influence of the electric field at a frequency of approximately 10 Hz (optical infrared range). The atomic polarizability cannot be determined directly but is normally small compared to the electronic polarizability. Electronic and atomic polarization occur in all types of polymer, even polymers with no permanent dipole moments. Polymers with permanent dipoles show no macroscopic polarization in the absence of an external electric field. If an alternative electric field is applied and if the electric field frequency is sufficiently low with reference to the jump frequency of segments of the polymer, the dipoles orient in the field and the sample shows not only electronic and atomic polarization but also a dipolar polarization. DETA, which operates in a frequency range from 10 to 10 Hz, is used to monitor dipole reorientation induced by conformational changes. These are referred to as dielectric relaxation processes. 

Both side groups and carbon-carbon double bonds can be incorporated into the polymer structure to produce highly resilient rubbers. Two typical examples are polyisoprene and polychloroprene rubbers. On the other hand, the incorporation of polar side groups into the rubber structure imparts a dipolar nature which provides oil resistance to these rubbers. Oil resistance is not found in rubber containing only carbon and hydrogen atoms (e.g. natural rubber). Increasing the number of polar substituents in the rubber usually increases density, reduces gas permeability, increases oil resistance and gives poorer low-temperature properties. 

In a similar reaction, but with reversed polarities in the starting materials 3-nitrobenzofuran adds to l-phenyl-2-pyrrolidinoacetylene to afford a mixture of three components, one being 5-nitro-3-phenyl-2-pyrrolidino-l-benzoxepin (3, 27 %).183 In the first step of this reaction, a bond between C2 of the furan and the carbon atom in the a-position to the phenyl group is formed to produce a dipolar intermediate that can react in different directions. 

Methyl ethyl ether is a gas at room temperature (boiling point = 8 °C), but 1-propanol, shown in Figure 11-13. is a liquid (boiling point = 97 °C). The compounds have the same molecular formula, C3 Hg O, and each has a chain of four inner atoms, C—O—C—C and O—C—C—C. Consequently, the electron clouds of these two molecules are about the same size, and their dispersion forces are comparable. Each molecule has an s p -hybridized oxygen atom with two polar single bonds, so their dipolar forces should be similar. The very different boiling points of 1-propanol and methyl ethyl ether make it clear that dispersion and dipolar forces do not reveal the entire story of intermolecular attractions. 

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