Dipole moments discussion

The latter correlation raises the question of why formation constants with H BA bases, acting as solutes in o-dichlorobenzene, should show a dependence on TT, which is a bulk solvent property. The rationale lies in the proportionality between solvent tt values and molecular dipole moments discussed in Section 1. The partial dependence on tt in Equation 1315 evidently reflects the complex-stabilizing effect of the interaction between the tributylammonium ion charge and the HBA base dipole. In future papers we shall show even more ex-... 

Raman scattering has been discussed by many authors. As in the case of IR vibrational spectroscopy, the interaction is between the electromagnetic field and a dipole moment, however in this case the dipole moment is induced by the field itself The induced dipole is pj j = a E, where a is the polarizability. It can be expressed in a Taylor series expansion in coordinate isplacement... 

In order to illustrate some of the basic aspects of the nonlinear optical response of materials, we first discuss the anliannonic oscillator model. This treatment may be viewed as the extension of the classical Lorentz model of the response of an atom or molecule to include nonlinear effects. In such models, the medium is treated as a collection of electrons bound about ion cores. Under the influence of the electric field associated with an optical wave, the ion cores move in the direction of the applied field, while the electrons are displaced in the opposite direction. These motions induce an oscillating dipole moment, which then couples back to the radiation fields. Since the ions are significantly more massive than the electrons, their motion is of secondary importance for optical frequencies and is neglected. 

The dipole moment for a calculation is reported and is contained in the log file if logging is turn ed on. It is also reported on the status line if you Display DipoleMoment on iheDisplay menu. Other expectation values besides the dipole moment (for example, qna-dnipole moment ) could he reported with a wave function but the set reported with this release of HyperChem is limited to on ly a few. Below we discuss the properties or oth er ch aracteri/ation s of the calculated wave function that can he interactively visnali/ed. 

Our discussion of elecfronic effects has concentrated so far on permanent features of the cliarge distribution. Electrostatic interactions also arise from changes in the charge distribution of a molecule or atom caused by an external field, a process called polarisation. The primary effect of the external electric field (which in our case will be caused by neighbouring molecules) is to induce a dipole in the molecule. The magnitude of the induced dipole moment ginj is proportional to the electric field E, with the constant of proportionahty being the polarisability a ... 

Another way to obtain a relative permitivity is using some simple equations that relate relative permitivity to the molecular dipole moment. These are derived from statistical mechanics. Two of the more well-known equations are the Clausius-Mossotti equation and the Kirkwood equation. These and others are discussed in the review articles referenced at the end of this chapter. The com-... 

Now let us examine the molecular origin of Molecular polarity may be the result of either a permanent dipole moment p or an induced dipole moment ind here the latter arises from the distortion of the charge distribution in a molecule due to an electric field. We saw in Chap. 8 that each of these types of polarity are sources of intermolecular attraction. In the present discussion we assume that no permanent dipoles are present and note that the induced dipole moment is proportional to the net field strength at the molecule ... 

Applications of MO methods to such diverse problems as aromaticity, tautomeric structure, dipole moments, and UV, NMR and PE spectroscopy are discussed in various monograph chapters. 

The spectrochemical data on 1,2- and 2,1-benzisoxazoles were reviewed in 1962 and reported on in greater detail in 1967 62HC(l7)l,p. 159, 62HC(17)l, p. 213, 67AHC(8)277). These reviews discuss tt-electron densities, bond order calculations and dipole moment studies for these ring systems. 

Oxirane (1) and methyloxirane (3) are miscible with water, ethyloxirane is very soluble in water, while compounds such as cyclopentene oxide and higher oxiranes are essentially insoluble (B-73MI50501) (for a discussion of the solubilities of heterocycles, see (63PMH(l)l77)). Other physical properties of heterocycles, such as dipole moments and electrochemical properties, are discussed in various chapters of pmh. The optical activity of chiral oxiranes has been investigated by ab initio molecular orbital methods (8UA1023). 

For more detailed discussion of dipole moments, see L. E. Sutton, in Determination of Organic Structures by Physical Methods, Vbl. 1, E. A. Braude and F. C. Nachod, eds., Academic Press, New York, 1955, Chapter 9 V I. Minkin, O. A. Osipov, and Y. A. Zhdanov, Dipole Moments in Organic Chemistry, Plenum Press, New York, 1970. 

This is not a unique way of classifying molecular properties. For example, Dykstra et al. (1990) concentrate on the response of a system to an apphed external field the electric dipole moment can be defined as the first derivative of the energy with respect to the field, and so on. I will stick with the Boys and Cook nomenclature as a broad basis for discussion. 

Molecules do not consist of rigid arrays of point charges, and on application of an external electrostatic field the electrons and protons will rearrange themselves until the interaction energy is a minimum. In classical electrostatics, where we deal with macroscopic samples, the phenomenon is referred to as the induced polarization. I dealt with this in Chapter 15, when we discussed the Onsager model of solvation. The nuclei and the electrons will tend to move in opposite directions when a field is applied, and so the electric dipole moment will change. Again, in classical electrostatics we study the induced dipole moment per unit volume. 

The tautomerism of the thiouracils has been discussed with reference to their ultraviolet speetra. Dipole moment studies of the mono- and di-thiouracils (211 X, Y — 0, S) and their various alkyl derivatives indicate that they all exist in the dioxo, oxothio, or di-thione form, and this has been confirmed by X-ray studies and,... 

Finally, two sets of physical properties have been correlated by the Hammett equation. Sharpe and Walker have shown that changes in dipole moment are approximately linearly correlated with ct-values, and Snyder has recently correlated the free energies of adsorption of a series of substituted pyridines with u-values. All the reaction constants for the series discussed are summarized in Table V. 

Electrical Conductivity in Non-aqueous Solvents. Let us now discuss the random motion of an atomic ion dissolved in methanol or ethanol. It will be seen from Table 41 that the value of the dipole moment on the OH group of these molecules differs little from that of the... 

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