Dipole molecular, induced

Place the following types of molecular and ion interactions in order of increasing magnitude (a) ion-dipole (b) induced-dipole-induced-dipole (c) dipole-dipole in the gas phase ... 

The main difference between a molecule-molecule (M-M) collision and an ion-molecule (M+-M) collision is the presence of a polarization force in the latter system owing to the attraction between the static charge on M+ and the dipole moment induced on M. For a large inter molecular separation, the polarization energy is known as... 

H-bonding is an important, but not the sole, interatomic interaction. Thus, total energy is usually calculated as the sum of steric, electrostatic, H-bonding and other components of interatomic interactions. A similar situation holds with QSAR studies of any property (activity) where H-bond parameters are used in combination with other descriptors. For example, five molecular descriptors are applied in the solvation equation of Kamlet-Taft-Abraham excess of molecular refraction (Rj), which models dispersion force interactions arising from the polarizability of n- and n-electrons the solute polarity/polarizability (ir ) due to solute-solvent interactions between bond dipoles and induced dipoles overall or summation H-bond acidity (2a ) overall or summation H-bond basicity (2(3 ) and McGowan volume (VJ [53] ... 

Dipole-induced dipole forces. A molecule with a strong molecular or bond dipole can induce a dipole in a molecule nearby that is polarizable. These Keesom forces have the same inverse 6th power dependence with distance. An example could be the interaction of chlorobenzene with naphthalene. 

Supermolecular spectra could perhaps be studied with state-selection using adequate molecular beam techniques. That would not be easy, however, because of the smallness of the dipole moments induced by in-termolecular interactions. For the purpose of this book, we will mostly deal with bulk spectra, or interaction-induced absorption of pure and mixed gases. A great variety of excellent measurements of such spectra exists for a broad range of temperatures, while state-selected supermolecular absorption beam data are virtually non-existent at this time. Furthermore, important applications in astrophysics, etc., are concerned precisely with the optical bulk properties of real gases and mixtures. 

The dielectric properties of gases are closely related to collision-induced absorption. It is well known that collisions modify molecular properties. Specifically, we are here interested in the dipole moments induced by collisions (Chapter 4) which manifest themselves not only in collision-induced absorption, but also in the dielectric virial properties of gases. 

Recall from Section 7-1 that the larger the atom, the greater its potential for forming induced dipole molecular interactions. 

By way of induced dipole—induced dipole molecular attractions. 

Polarizability is a measure of the ease with which the electrons of a molecule are distorted. It is the basis for evaluating the nonspecific attraction forces (London dispersion forces) that arise when two molecules approach each other. Each molecule distorts the electron cloud of the other and thereby induces an instantaneous dipole. The induced dipoles then attract each other. Dispersion forces are weak and are most important for the nonpolar solvents where other solvation forces are absent. They do, nevertheless, become stronger the larger the electron cloud, and they may also become important for some of the higher-molecular-weight polar solvents. Large solute particles such as iodide ion interact by this mechanism more strongly than do small ones such as fluoride ion. Furthermore, solvent polarizability may influence rates of certain types of reactions because transition states may be of different polarizability from reactants and so be differently solvated. 

In molecular solids, atoms or molecules bond using hydrogen bonds or dipole-dipole dispersion forces. This bond occurs when temporary dipoles are induced in adjacent atoms. 

The polarizability (a) describes the ease with which molecular orbitals are deformed by the presence of an external electric field (E) (Stevenson and Vo-Dinih, 1996). The dipole moment induced (P) on a molecule by the presence of E is most generally described by the following equation ... 

The fundamentals of the Raman effect can be understood by consideration of a classical model, in which an incident beam of radiation (i.e., laser beam, for all practical purposes, in flame diagnostics) passes through an ensemble of molecules. The resultant laser beam electric field distorts the electronic cloud distribution of each molecule, causing oscillating dipoles these induced dipoles are related to the incident laser beam electric field by the molecular polarizability. The dipoles, in turn, produce a secondary radiating field at essentially the same frequency as that for the incident beam. This radiation is termed Rayleigh scattering. 

Bersohn 76) has calculated the crystal field created by the molecular dipoles in the lattice of CH3C1. The static dipole moment of the molecules induces through the polarizability of the molecules an additional dipole moment which increases the dipole moment of the free molecule by a factor of about 1.05. This in turn means that the C—Cl bond has increased in ionic character under the influence of the intermolecular electric fields and therefore (see Eq. (II.9 the quadrupole coupling constant will be lower relative to the gaseous state. Besides the dipole moment induced in the direction of the static dipole, a perpendicular partial moment should be induced, too. Therefore the axial symmetry of the C—Cl bond will be disturbed and the asymmetry parameter 77 may become unequal zero. A small asymmetry parameter 17 = 0.028 has been observed for the nuclear quadrupole interaction in solid CH3I. Bersohn also calculated from the known crystal structure of 1,3,5-trichlorobenzene the induced... 

The LSER approach relates a bulk property, P, to molecular parameters thought to account for cavity formation, dipole moment/polarizability, and hydrogen-bonding effects at the molecular level. The cavity term models the energy needed to provide a solute molecule-sized cavity in the solvent. The dipole moment/polarizability terms model dipole and induced dipole interactions between solute and solvent these can be viewed as related to dispersion interactions. The hydrogen-bonding terms model HBA basicity and EIBD acidity interactions. 

The difficulty In distinguishing permanent dipole from Induced dipole moment effects In a molecular beam deflection... 

Figure 2.4-3 Molecular dipole moment induced by an electric field.

Molecular Theory for a Molecular Dilute State. In presenting the theory of the Kerr effect, we shall begin with the simple case of a molar volume Im free of molecular fields. This is equivalent to assuming the relation (145) for the dipole moment induced in molecule i by the electric field of the light wave Eo(r, t). Equations (142)—(145) now yield the molar refraction in the presence of an electric field E(0) in the form ... 

Collision-induced Dipoles. Even in materials whose molecules possess no permanent dipole, molecular collisions, either of unlike molecules or of like molecules in skew attitudes, produce fluctuating dipoles whose time variation reflects the translational movement of the colliding molecules rather than any characteristic vibration of the molecules. This effect appears in its purest form in m lxtures of rare gases. 

Although the momentary dipoles and induced dipoles are constantly changing, the net result is attraction between the two molecules. These van der Waals forces have a very short range they act only between the portions of different molecules that are in close contact, that is, between the surfaces of molecules. As we shall see, the relationship between the strength of van der Waals forces and the surface areas of molecules (Sec. 3.12) will help us to understand the effect of molecular size and shape on physical properties. We must not underestimate the power of these weakest intermolecular forces acting between non-polar chains of phospholipids, for example, they are the mortar in the walls of living cells. 

Instantaneous dipole / induced dipole At any specific moment the electron cloud is not necesarily symetrical, this instantaneous dipole then induces a dipole in another molecule and they are attracted, this is the weakest of all molecular interactions. 

The application of an electric field always causes some physical changes in the medium even if the liquid molecules are non-polar, the electrons in the molecule will be affected by the electric field. The movement of electrons within the molecule results in an induced dipole, ft, and the alignment of the induced dipoles with the electric field gives induced polarization. For example, if a positive charge is placed above the plane of a neutral benzene molecule, the average positions of the electrons will shift upward, giving the benzene molecule a dipole moment whose direction is perpendicular to the molecular plane. In summary, when a non-polar molecule is subjected to an electric field, the electrons in the molecule are displaced from their ordinary positions so that the electron clouds and nuclei are attracted in opposite directions and a dipole is induced thus the molecule temporarily has an induced dipole moment, ft. 

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