D Orbital overlap

However, there is evidence against d-orbital overlap and the stabilizing effects have been attributed to other causes. In the case of a PhS substituent, carbanion stabilization is thought to be due to a combination of the inductive and polarizability effects of the group, and d-pn resonance and... 

Only 5% of the cis isomer, tiglic acid, was produced. In addition, certain carbanions in which the negative charge is stabilized by d-orbital overlap can maintain configuration (p. 233) and SeI reactions involving them proceed with retention of configuration. 

In order to discuss the density of states of metal surface atoms, we need to take a closer look at those orbitals that have a distinct orientation, the d-orbitals. Let us take an fee crystal and see how the d-orbitals combine to form bands. Figure A.7 schematically shows the shape of the d-orbitals. For clarity only the lobes in the (yz) plane are shown, while the toroidal component of the dz2 orbital has been left out. If these orbitals are placed within the fee structure as in Fig. A.7, one readily sees that the best overlap between nearest neighbors in the (yz) or (100) plane occurs between the dyz orbitals, whereas the orbitals along the y and z axes of the cube overlap to a much smaller extent. This is true in the other planes of an fee metal as well, the dtv, dxz, and d orbitals overlap more than the d,2 and the dx2.v2... 

Fio. 10. The molecular orbitals of the allyl group a (tli bonding), b nonbonding), and c 1/13 antibonding), and d, the metal d orbital overlap with ijif... 

In the sodium chloride structure, the symmetry enables three of the five d orbitals on different atoms to overlap. Because the atoms are not nearest neighbours, the overlap is not as large as in pure metals and the bands are thus narrow. The other two d orbitals overlap with orbitals on the adjacent oxygens. Thus, two narrow 3c/ bands exist. The lower one, labelled 2g. can take up to 67Velectrons, and the upper one, labelled 6g, up to 47V electrons. Divalent titanium has two d electrons, therefore, 27V electrons fill the 37V levels of the lower band. Similarly, divalent vanadium has three d electrons and so the lower band is half full. As in the case of pure metals, a partly filled band leads to metallic conductivity. For FeO, the /2g band would be full, so it is not surprising to find that it is a semiconductor but MnO with only five electrons per manganese is also a semiconductor. 

Figure 2.2. Illustration of d-orbital overlap between adjacent metal atoms in an extended metallic network.

FIGURE 10-10 Overlap of d, TT, and p Orbitals with Metal d Orbitals. Overlap is good with ligand d and TT orbitals, but poorer with ligandp orbitals. 

FIGURE 8.5 Bonding and antibonding molecular orbitals (MOs) formed from d-orbital overlap, (a) orbitals along the internuclear axis, (b) tt and tt MOs formed from side-by-side overlap of orbitals in the x-z plane (there is a corresponding pair of MOs formed from side-by-side overlap of c/ orbitals in the y-z plane), (c) S and S orbitals from the face-to-face overlap of a pair of MOs (there is a corresponding pair of MOs constructed from the orbitals, which are rotated 45 from the set shown here). 

In NiO, for example, divalent nickel has eight d-electrons, which gives rise to two unpaired electrons in the e set for octahedral coordination. It crystallizes with the sodium chloride structure, where the nickel d-orbitals overlap with the oxide p-orbitals along each cell edge. For example, each nickel has one electron in the d j orbital which can interact with the electron in the oxygen p orbital and form an antiparallel spin pair. The other electron in the oxygen p orbital must be antiparallel to that, as it is in the same orbital as the other oxygen electron and each orbital can contain only two electrons of opposite spin. The other... 

It was proposed that the specific adsorption on the APTES coated crystals occurred through H-bonding, dipole-dipole and n-so d orbital overlap. The sensor can be successfully used for the... 

With ligands that behave as both tt acceptors and tt donors (such as CO and CN ), the TT-acceptor nature predominates. Although Tr-donor ligands cause the value of to decrease, the larger effect of the 7r-acceptor ligands causes to increase. The net result of pi-acceptor ligands is an increase in A , mostly because d orbital overlap is generally more effective with tt orbitals than with Tr-donor orbitals. 

Figure 2.7 shows that the ethylene is coordinated to the titanium center at the vacant octahedral position through sigma bonding involving the ethylene 7t-orbitals and the titanium d orbital. The 7t-bond involves titanium d orbital overlapping with empty Tt-antibonding orbitals on ethylene. The coordination of ethylene to the titanium active site is known as the Dewar-Chatt-Duncanson model of the metal-olefin bond [31]. The... 

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