Electron density redistribution

The free energy of activation at the QCISD(T)/6-31 H-- -G(d,p) level amounts to 21.1 kcal/mol. According to the authors, the large electron density redistribution arising upon cyclization makes it necessary to use extended basis sets and high-order electron correlation methods to describe the gas-phase thermodynamics, which indicates clearly the gas-phase preference of the azido species. However, the equilibrium is shifted toward the tetrazole as the polarity of a solvent is increased. For instance, SCRF calculations (e = 78.4) yield a relative free energy of solvation with respect to the cw-azido isomer of —2.4 kcal/mol for the tmns-zziAo compound and of —6.8 kcal/mol for the tetrazole isomer. At a much lower level, the... 

For the C02 Cjo cluster, the translational frequencies e = 54 cm-1 and a [ = 122 cm-1 are smaller than for C2H2 C7o both these vibrations are coupled to the deformation vibrations of the guest and the cage. According to the Mulliken population analysis, there is some electron density redistribution and an increase of polarity of the both M-X bonds in the encapsulated guests, as compared to the free molecules BeF2 and CO2 (induced polarization). 

These theoretical results discussed in the preceding paragraph are fully consistent with the experimental XPS and UPS data. Indeed, the new features appearing on the C(ls), S(2p), and Al(2p) XPS spectra constitute dear evidence of the charge transfer from aluminum to carbon and sulphur. Other model configurations, where the aluminum atoms are made to interact either only with the sulphur atoms or only with the 0-carbon atoms, are calculated to be much less stable than the Al—C structure described above, and do not result in any electron density redistribution consistent with the XPS results. The inert character of the 0-carbons, and of the adjacent thiophene units, upon reaction of aluminum with a given thiophene unit also is reflected in the spectra, as the major part of the C(ls) and S(2p) contribution remains unshifted when aluminum is deposited... 

Besides the changes in the dipole moment, the electron density redistribution induced upon solvation can also be examined from the changes in the molecular electrostatic potential [66-68], or the variation in the molecular volume [69], These studies have identified specific trends for the solvation of neutral, polar solutes and charged species. In the former case, solvation in polar solvents is accompanied by an electron shift from the... 

Real denotes the full system, which only needs to be calculated at the lowest computational level. The additional system is defined as the model system. This type of adsorption results in the polarization and the electron density redistribution of GB and GD on the surface of the mineral. This corresponds to the formation of attractive contacts between GB and GD agents and the surface of dickite. 

The examples presented in this work by no means cover the subject of the C-H bond activation on a spectrum of catalytic media. Interaction of methane with the small clusters discussed here obviously cannot pretend to fully mimic catalytic centers in reality. Nevertheless, they seem to justify drawing generalized conclusions regarding the mechanism of catalytic activation in terms of electron withdrawal or donation to the interacting hydrocarbon molecule. A variety of properties contribute consequently to the emerging scheme (electronic density redistribution, geometry evolution in critical points, energetical factors, vibrational analyses) which substantially increases credibility of the conclusions. 

The process of electron density redistribution during charge-transfer interaction is accompanied by the more significant decrease in the system energy than in the case of van der Waals interactions. This suggests that the bond in the forming systems is stronger. 

Fluoride anion strongly interacts with various inorganic and organic boron and silicon compounds. These reactions are the basis for several fluoride sensors. Interaction of fluoride with boron compounds results in electron density redistribution and may also induce structural changes. Formation of fluoride complex by ferrocene derivative (Figure 16.19a) results in a decrease of oxidation potential by 200 mV... 

A number of locations and orientations of Sarin on the regular nanosurface and on the small fragment of MgO were found. In this study it was revealed that Sarin is physisorbed (the nanosurface and hydroxylated small fragment this is undestructive adsorption) or chemisorbed (destructive adsorption) on MgO (see Figure 16-1). The physisorption of GB on the surface of MgO occurs due to the formation of hydrogen bonds and ion-dipole and dipole-dipole interactions between adsorbed GB and the surface. The chemisorption occurs due to the formation of covalent bonds between the molecule and the surface. The adsorption results in the polarization and the electron density redistribution of GB. The adsorption energy obtained at the MP2/6-31G(d) level of theory for the most stable chemisorbed system is... 

The first section in this chapter focuses on HCN as an element in a chain of H-bonded units. The presence in this molecule of only one proton and one lone electron pair provides a simple testing ground for ideas about cooperativity. The linearity of the complex also simplifies analysis of electron density redistributions caused by multiple bonding. HCCH is similar in some ways, but its absence of a lone electron pair causes significant distinctions. 

Some formal analogy between secondary bonding and hydrogen bonding can be noted. In both cases, there is a trinuclear. basically linear (but not always) and unsym-metrical X-A X system, in which A-X is a normal covalent bond, and A X is a weaker interaction, called an hydrogen bond (when A = H) and secondary bond (when A /f)(Scheme 1). In rare cases, the hydrogen bonds are symmetrical, and this happens more often with secondary bonds. Symmetrical X" A "X systems are formed by an electron density redistribution by which the covalent bond is elongated, and the secondary bond is shortened, until the interatomic distances are equalized. In this case, the A X bond order is 0.5, sensibly more than in common secondary bonds. 

The Tc electron density redistribution in substituted ketenes cannot adequately be described by canonical forms. Usually it is assumed (89c,89rf) that resonance form B is of particular importance for the description of the tt elcc-... 

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