Interaction dipole moments

The angles ot, p, and x relate to the orientation of the dipole nionient vectors. The geonieti y of interaction between two bonds is given in Fig. 4-16, where r is the distance between the centers of the bonds. It is noteworthy that only the bond moments need be read in for the calculation because all geometr ic features (angles, etc.) can be calculated from the atomic coordinates. A default value of 1.0 for dielectric constant of the medium would normally be expected for calculating str uctures of isolated molecules in a vacuum, but the actual default value has been increased 1.5 to account for some intramolecular dipole moment interaction. A dielectric constant other than the default value can be entered for calculations in which the presence of solvent molecules is assumed, but it is not a simple matter to know what the effective dipole moment of the solvent molecules actually is in the immediate vicinity of the solute molecule. It is probably wrong to assume that the effective dipole moment is the same as it is in the bulk pure solvent. The molecular dipole moment (File 4-3) is the vector sum of the individual dipole moments within the molecule. 

As argued above, this result is found to work best for substances in which both the 1,1 and 2,2 forces are either London or dipole-dipole. Even the case of one molecule with a permanent dipole moment interacting with a molecule which has only polarizability and no permanent dipole moment-such species interact by permanent dipole-induced dipole attraction-is not satisfactorily approximated by Eq. (8.46). In this context the like dissolves like rule means like with respect to the origin of intermolecular forces. 

A molecule must have a permanent dipole moment to be micro-wave active. As it rotates, the changing dipole moment interacts with the oscillating electric field of the electromagnetic radiation, resulting in absorption or emission of energy. This requirement means that homonuclear molecules such as H2 are microwave inactive, but heteronuclear molecules such as SO3, S02, NO and, of course, H20 are active. 

Also a molecule with a static dipole moment interacts with a polarisable molecule. If the dipole can freely rotate, the Helmholtz free energy is... 

FIGURE 10.8 A fluctuation of the electron distribution on one atom induces a corresponding temporary dipole moment on a neighboring atom. The two dipole moments interact to give a net attractive force, called a "dispersion force."... 

Dipole moment interactions 955 Diquinocyclobutene, synthesis of 1292 Directed ortho metalation (DoM) reaction 781, 792... 

Ferromagnetic 6c Large (below Oc) Above 0c, X = d(T- 0), with 0 = 0c Below 0c, Ms(T)IMs(0) against T/0c follows a universal curve above 0c, none Atoms have permanent dipole moments interaction produces parallel alignment... 

Antiferromagnetic 0N As paramagnetic Above 0N, X = CI(T 0). with 0 3t 0N. below 0N, X decreases, anisotropic None Atoms have permanent dipole moments interaction produces antiparallel alignment... 

The electronic spin-orhit terms Hls) i e., the corresponding magnetic dipole moment interactions related to the term H3 in the Breit Hamiltonian... 

One of the two or both nuclei of a diatomic molecule may interact with rotation via their electric quadrupole moments, or their magnetic dipole moments may interact with the rotational magnetic field. The two nuclei may be coupled by the direct (tensorial) or indirect (electron-coupled scalar) magnetic dipole interaction which also influences rotation. Furthermore, in a state other than E the nuclei cause magnetic perturbations when their dipole moments interact with those of the unpaired - electron spins or with the orbital magnetic field. The energetic effects of these so-called hyperfine interactions can be quantified with the aid of interaction constants which in favorable cases can be determined from high-resolution spectra. 

Polar interactions where molecules having permanent dipole moments interact in solution with the dipole orientation in a symmetrical manner. It follows that the geometric mean rule is obeyed for orientation interactions and the contribution of dipole orientations to the cohesive energy and dispersion interactions. 

The way that transition dipole moments interact together in multichro-mophore assemblies was initially examined by Kasha in his pioneering work on excitonic coupling. The original point dipole treatment was later refined by Hunter and Sanders who have developed a transition monopole treatment that allows quantitative prediction of the effects of excitonic interaction. Figure 13.4 qualitatively summarizes the nature of the absorption band shifts depending on the... 

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