Interaction charge-dipole

This fomuila does not include the charge-dipole interaction between reactants A and B. The correlation between measured rate constants in different solvents and their dielectric parameters in general is of a similar quality as illustrated for neutral reactants. This is not, however, due to the approximate nature of the Bom model itself which, in spite of its simplicity, leads to remarkably accurate values of ion solvation energies, if the ionic radii can be reliably estimated [15],... 

As charge-dipole interaction between the electron and the atom is small, the perturbation theory expansion may be used to estimate f. The odd terms of this expansion disappear after averaging over impact parameters due to isotropy of collisions. In the second order approximation only those elements of P that are bilinear in V are non-zero. Straightforward calculation showed [176] that all components of the Stark structure are broadened but only those for which m = 0 interfere with each other ... 

Where a is the unit vector defined by the local frame defining the axial quadupole, r is the vector oriented towards r from the monopole to the axial quadupole. Qa is the corresponding matrix element. Following the modification of the charge-dipole interaction, we introduced a modified mono-quad interaction, namely I -mono-quad1 ... 

It is instructive to compare these predictions with the results of computer simulations. This comparison, however, requires care. In practice, the computed values of A A exhibit considerable system-size dependence, i.e., they vary with the size of the simulation box. This is because charge-dipole interactions between the solute and... 

To explain the extraordinarily large ion—polar molecule reaction cross section, Theard and Hamill (1962) included the charge—dipole interaction as... 

There is thus an apparent continuity between the kinetics of an electron transfer leading to a stable product and a dissociative electron transfer. The reason for this continuity is the use of a Morse curve to model the stretching of a bond in a stable product in the first case and the use of a Morse curve also to model a weak charge-dipole interaction in the second case. We will come back later to the distinction between stepwise and concerted mechanisms in the framework of this continuity of kinetic behavior. 

The stretch-bend, torsional, electrostatic and VdW terms in MM3 are identical in form to the corresponding ones in MM2 (although the electrostatic treatment in MM3 also includes charge-dipole interactions and the VdW terms have slightly different numerical coefficients) and will not be further discussed here. 

Perchlorate and nitrate, as well as the halides, are less mobile relative to their size than the tetrafluoroborate and hexafluorophosphate ions. Anions that lie below the upper curve in Fig. 3 appear to undergo interaction with acetonitrile to a greater extent than would be expected on the basis of simple charge-dipole interaction, but the nature of this interaction is difficult to postulate. The fluoro ions should less likely undergo specific interactions. Because the differences in mobilities are not great, however, extensive speculation is unwarranted. 

The small 110 a.a. ribonuclease from B. amyloliquefaciens, bamase, has been studied extensively in A.R.Fersht s laboratory (Sali, Bycroft and Fersht, 1988 Matouschek et al, 1990 Bycroft et al., 1990 Serrano and Fersht, 1989) using NMR as an essential experimental techniqne. The df-helices of bamase have been studied with respect to stability and it was found that mutation of the THR and THR residnes located at the N-terminal of the helix (Serrano and Fersht, 1989) could destabilize the protein with up to 2.5 kcal mol b The THR and SER residnes are capable of facilitating the formation of an additional hydrogen bond in the first him of the df-helix. If THR is snbstitnted with ASP or GLU no marked change in stability was observed, probably dne to the known charge-dipole interaction between the negative charge of the ASP or GLU and the positive end of the helix macro-dipole. 

In summary, controversy concerning the mechanism for solvolysis at tertiary carbon is semantic and can be avoided by making a clear distinction between (a) nucleophilic solvation, which is stabilization of the transition state for stepwise solvolysis through carbocation or ion pair intermediates by charge-dipole interactions with nucleophilic solvents (Scheme 2.8A) and, (b) nucleophilic solvent participation, which is stabihzation of the transition state for concerted solvolysis by formation of a partial covalent bond to the solvent nucleophile (Scheme 2.8B). 

Two later sections (1.6.5 and 1.6.6) look at the crystalline structures of covalently bonded species. First, extended covalent arrays are investigated, such as the structure of diamond—one of the forms of elemental carbon—where each atom forms strong covalent bonds to the surrounding atoms, forming an infinite three-dimensional network of localized bonds throughout the crystal. Second, we look at molecular crystals, which are formed from small, individual, covalently-bonded molecules. These molecules are held together in the crystal by weak forces known collectively as van der Waals forces. These forces arise due to interactions between dipole moments in the molecules. Molecules that possess a permanent dipole can interact with one another (dipole-dipole interaction) and with ions (charge-dipole interaction). Molecules that do not possess a dipole also interact with each other because transient dipoles arise due to the movement of electrons, and these in turn induce dipoles in adjacent molecules. The net result is a weak attractive force known as the London dispersion force, which falls off very quickly with distance. 

Polar molecules can also interact with ions in a charge-dipole interaction which is about 10 to 20 times weaker than ion-ion interactions, and which decreases with distance... 

Charge-dipole interaction, 307, 446 CHARMM, 52, 60, 99, 408, 476, 482-483 CHELPG, see Atomic partial charge, ESP)... 

Electrostatic Forces. Electrostatic forces are of three main types charge-charge interactions, charge-dipole interactions, and dipole-dipole interactions. The energy of interaction between two charges Q, and Q2 is proportional to the... 

Based on the fundamental charge-dipole interaction, hydrogen bonding need not necessarily mandate the presence of lone electron pairs in the guest anion. If present, this electronic feature dominates the supramolecular behaviour of anions. As a corollary, it is the most prominent aspect to be removed in the construction of so-called non-coordinative anions (BPhj, BHj, closo-CBnHf2 etc.) that are required in the isolation and study of reactive cationic... 

Another important feature of the extracoordinate silicon compounds (Scheme 7.14) is the increase in natural atomic charge at the central atom compared to the tetracoordinate precursors [69]. The counter-intuitive increase in the positive charge on silicon, which becomes even more substantial in the case of anionic nucleophiles, such as F , is compensated by a more negative character of the surrounding groups (X), and this results in an enhanced ionic nature of the Si-X bond. This polarization then favors intermolecular charge-dipole interaction, which results in an increased Lewis acidity of the hypercoordinate silicon [70]. 

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