Intermolecular interactions dipole moments

The Rh-Rh distance is 3.12 A, long compared with Rh-Rh single bonds (2.624A in Rh2(MeCN) J([, 2.73 A in Rh4(CO)12) there is a weaker (3.31 A) intermolecular attraction. Dipole moment and IR studies indicate that the structure is retained in solution and is, therefore, a consequence of electronic rather than solid-state packing effects. Furthermore, it is found for some other (but not all) [RhCl(alkene)2]2 and [RhCl(CO)(PR3)]2 systems. SCF MO calculations indicate that bending favours a Rh-Cl bonding interaction which also includes a contribution from Rh—Rh bonding [56b]. 

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. 

The linear polarizability, a, describes the first-order response of the dipole moment with respect to external electric fields. The polarizability of a solute can be related to the dielectric constant of the solution through Debye s equation and molar refractivity through the Clausius-Mosotti equation [1], Together with the dipole moment, a dominates the intermolecular forces such as the van der Waals interactions, while its variations upon vibration determine the Raman activities. Although a corresponds to the linear response of the dipole moment, it is the first quantity of interest in nonlinear optics (NLO) and particularly for the deduction of stracture-property relationships and for the design of new... 

G2, to G3, and to G4, the effective enhancement was 10%, 36%, and 35% larger than the value estimated by the simple addition of monomeric values. The enhancement included the local field effect due to the screening electric field generated by neighboring molecules. Assuming the chromophore-solvent effect on the second-order susceptibility is independent of the number of chro-mophore units in the dendrimers, p enhancement can be attributed to the inter-molecular dipole-dipole interaction of the chromophore units. Hence, such an intermolecular coupling for the p enhancement should be more effective with the dendrimers composed of the NLO chromophore, whose dipole moment and the charge transfer are unidirectional parallel to the molecular axis. 

Intermolecular forces may be caused by a solute molecule having a dipole moment, when it can interact selectively with other dipoles. If a molecule is a good proton donor or acceptor it can interact with other such molecules by hydrogen bonding. Molecules can also interact via much weaker dispersion forces which rely on a given molecule being polarised by another molecule. 

The aggregation-induced changes of absorption spectra result from intermolecular interactions between closely spaced carotenoid molecules. For two molecules whose transition dipole moment vectors, p, are located at places characterized by position vectors /- and r2, with the relative position vector defined as R=r1-r2, Figure 8.3, the interaction energy is expressed as (van Amerongen et al. 2000)... 

The intermolecular interaction described above provides information about the magnitude of spectral shifts, but it does not explain why the absorption spectra of molecular aggregates usually have either an H- or J-band. The square of transition dipole moment (in Debye2 units) is usually termed the dipole strength and is related to the intensity of the absorption band as (van Amerongen et al. 2000)... 

Keywords Dipole moment Fluorescence Hydrogen bond Intermolecular interactions Solvatochromism... 

Table 4.3. Water dimer properties the interaction energy (Ei t) in kcal/mol, the intermolecular distance (R00) in A, and the dipole moment p. in Debye, calculated using the B88/P86 exchange-correlation functional and different basis sets.

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