Bond dipole moment calculation

Molecular dipole moment (Section 1.11) The overall measured dipole moment of a molecule. It can be calculated as the resultant (or vector sum) of all the individual bond dipole moments. 

Since the elementary quantum-mechanical treatment does not seem to give a high enough barrier, various treatments of the problem have been proposed which use empirical data such as bond dipole moments and steric repulsive forces. These treatments do not introduce any new forces which would not be included in a proper quantum-mechanical analysis, but they attempt to short-circuit these difficult and uncertain calculations. 

The dipole moment calculated for 111 is somewhat higher than for 96, as expected. The total it charge in the cyclopentadiene ring is calculated to be 0.54 electrons. A somewhat smaller polarization, 0.40 tt electrons, is calculated for 7,8-diphenylcalicene (124), and 0.34 tt electrons for hexaphenylcalicene 115, (122) by the PPP (Pariser-Parr-Pople) method. Thus it seems as if the tt polarization roughly follows the same trend as the bond lengths and the C=C torsional barriers. 

The magnitude of the surface dipole. For the system hydrogen-nickel, formula (13) leads to a value of 0.66 D. The experimentally determined value 0.022 D. is therefore a factor of about 30 smaller. This is quite conceivable because (13) has been derived for a diatomic molecule. In our case one of the partners of the bond, the metal, has a very high polarizability, and hence the surface dipole will be quenched to a large extent. The value of the dipole moment calculated from (13), though larger than the experimental value, is still far smaller than that to be expected for a pure ionic bond (fora bond distance of 2 A. fj, = 10 D.). This is one of the reasons for us to think that the contribution of the ionic type M+X to the total bond... 

Two types of parameters appear in this expression, m/ represents bond dipole moments, while dm/ / d/ /. represents derivatives of the bond dipole moment with respect to the internal coordinates (bond stretching, angle deformation, out-of-plane deformation, and torsion). These parameters are referred to as electro-optical parameters (eop). All other quantities are derived from the structure or from the normal coordinate calculation. The electro-optical parameters can be derived from measured intensities, like force constants are derived from measured frequencies. Compared to the determination of force constants, the problem in this case is that the number of parameters is much higher. 

In addition to solubility and cryoscopic studies, the association of solute molecules may be investigated by the variation of the dielectric constant with concentration. If the solution is non-polar, the value of the dipole moment calculated from the value of the dielectric constant at infinite dilution, obtained by extrapolation, may be close to the value obtained in the gaseous phase. If this be so, there are no anomalous solvent effects, but cases exist where this is not so and such behaviour may be explained by two theories. The first assumes that association of solute molecules persists at low concentrations and may be illustrated with reference to the curious variation of polarization of ethyl alcohol in hexane solution. As the concentration is increased, the polarization falls, passes through a minimum, rises to a maximutn value and then falls to the value for the polarization of pure ethyl alcohol. In dilute solution the molecules are evidently associated in such a way that the dipole moment is decreased, this may occur through the formation of quadrupoles by means of hydrogen bonds, viz... 

As a further extension of the method, the interbond angle of the carbonyl groups of derivatives of the type CpFe(CO)2X have been calculated by extending the method of oscillating dipoles to the second derivative of the carbonyl bond dipole moment 91). The results obtained are in remarkable agreement with those calculated using the absolute intensities of the fundamental carbonyl stretching vibrations (52). 

In summary, from the considerable study that has been made of pentacarbonyl metal complexes, there is some doubt about the adequacy of the CKM for the calculation of both relative and absolute intensities (26, 53). Measured intensities obtained from different laboratories lead to differing results (2, 53,136). Evidence suggests that individual carbonyl bond dipole moments exist (85, 123) and that solvent effects could cause the coexistence of characteristic dipole moment derivatives for the various modes (Section V). In any case, the existence of the latter has, independent of solvent... 

Introduction. The use of electrical measurements has been fairly important in the study of H bond association. In the main, this is the result of three facts (1) the experimental quantities are readily obtained (2) dipole moments calculated from the measured quantities have directionally additive properties and therefore can often allow a choice between various possible structures (3) dielectric dispersion studies permit separation of the several kinds of rearrangements that occur. The experimental determinations have increased in complexity as more extensive ranges of frequency are scanned in studying dielectric dispersion, as biological and polymeric substances become of interest, and as improved theories demand more accurate data. The advantage of the directional aspects of the dipole vector is somewhat nullified by extraneous effects of the solvent and of parts of the molecule not involved in H bonding. 

Low values of 6 are usually found in m/ramoleculeirly H bonded substances. (Intramolecular H bonds are discussed in Chapter 5.) The arrangement of atoms within a molecule and, with less confidence, of molecules in a polymeric unit can be determined by comparing the measured dipole moment with values calculated by the vectorial addition of bond dipole moments for various arrangements. 

Integrated i.r. intensity data have been used to calculate bond moments and their derivatives [453] the calculated dipole moment was -0.93 D (3.10 x 10" ° C m), compared with an experimental value (Stark effect upon the microwave spectrum) of -0.95 D (3.17 x 10-30 c m) [1215]. The original vibrational intensity data for COFj [981] has now been corrected [1363], and the CNDO/2 calculations [1827] of the dipole moment derivatives have been revised [289,292,1363,1417] many of the bond moment derivatives (the squares of which are approximately proportional to band intensities) were shown to be transferable [1675]. Bond dipole moments have also been calculated by ab initio methods (with a STO 5-31G basis set) [1941]. In addition, the dipole moment derivatives have been calculated under the MINDO/3 formalisms [1586], but little reliance can be placed on the results obtained. 

Exploiting the charge transfer information encoded by the matrix CT, the algebraic semisum charge-transfer index, denoted as p. g, was proposed as a measure of the molecular dipole moment calculated as the half-sum of the GTy elements corresponding to pairs of bonded... 

N.m.r., X-ray photoelectron studies, and extended Huckel calculations on HgCl2Py2 indicate a moderate amount of electron transfer to the metal from pyridine relative to ZnQ2py2 the filled mercury d-orbitals do not participate in bonding. Dipole moment studies on Cdl2py2 have been made, while stability constant studies for the formation of complexes between Cd and pyridine in water, water-MeOH, and water-DMF mixtures show the formation of the species [CdlpylJ (x = 1—3). A structural determination of Hg(N03)2(py)2(H20)2 reveals mercury in a distorted octahedral environment consisting of two water and two pyridine ligands (Hg—N =... 

Germanium(iv) bromide has been reinvestigated by electron diffraction. Constraining the molecule symmetry to afforded a value of 2.272(1) The electronic radial distribution functions for germanium(iv) and tin(iv) chlorides in the liquid state at 23 °C have been calculated from X-ray diffraction intensity distributions obtained by use of theta-theta reflection diffractometry. Both liquids show intermolecular effects at distances equivalent to the Cl—Cl intermolecular distance. Values of 0.9 D (Si—Cl), 1.5 D (Ge—Cl), and 2.7 D (Sn—Cl) have been derived for the bond dipole moments of these bonds in the metal(iv)... 

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