Orbitals, antibonding nonbonding

All lone pair orbitals have a node between the two atoms and, hence, have a slightly antibonding character. This destabilizing effect of the lone pair localized molecular orbitals corresponds to the nonbonded repulsions between lone pair atomic orbitals in the valence bond theory. In the MO theory all bonding and antibonding resonance effects can be described as sums of contributions from orthogonal molecular orbitals. Hence, the nonbonded repulsions appear here as intra-orbital antibonding effects in contrast to the valence-bond description. 

Three p AO s give three molecular orbitals, as indicated in Fig. 8-4. Since there are an odd number of p AO s in this linear system, the middle-energy molecular orbital is nonbonding (w"). Note that the node of this MO" is at a C, indicated by a 0. An MO" can be recognized if the number of bonding pairs equals the number of antibonding pairs (see Problem 8.26) or if there is no overlap. 

March J., Advanced Organic Chemistry, 4th edn, John Wiley Sons, Inc., New York, 1992, p. 573. 146Certain semi-empirical calculations (extended Hiickel, CNDO, etc.) orient the large lobes away from each other in the o orbital. Such an orbital is nonbonding rather than antibonding, because the two AOs hardly interact. 

Ti02, there is much more than a guess at a DOS. There is a chemical characterization of the localization in real space of the states (are they on Pt on H on Ti on O ) and a specification of their bonding properties (Pt-H bonding, antibonding, nonbonding, etc.). The chemist asks right away, where in space are the electrons Where are the bonds There must be a way that these inherently chemical, local questions can be answered, even if the crystal molecular orbitals, the Bloch functions, delocalize the electrons over the entire crystal. 

The tetracobalt cubanes [ Co(/Li3-S)Cp 4] (67) (M = Co, E = S) have not been studied as extensively as the iron analogues (Section IV,B), but it is to be expected that electrochemical studies will reveal an extensive electron-transfer series. A comparison of the structures of [ Co(/i3-S)Cp 4] (2 = 0 and 1) showed that the nonbonded tetrahedron of metal atoms in the neutral molecule (Co—Coave = 329.5 pm) undergoes a tetragonal distortion. The shortening of four of the cobalt-cobalt distances (317.2 pm) is due to the removal of an electron from an orbital antibonding with respect to the four metal atoms 190). 

In addition to the orbital energies, PES provides a great deal of information about the nature of the orbital (bonding, nonbonding, or antibonding) from the vibrational fine structure observed in the spectra. 

Compare and contrast the following three concepts (a) bonding orbitals (b) antibonding orbitals (c) nonbonding orbitals. 

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