Orbitals, antibonding degenerate

As in the Isa orbitals, mutual orthogonality of the two in each of the pairs shown in Fig. 3.2 is assured by the fact that one is g and the other is u. The four orbitals are degenerate at infinite R b but the degeneracy is split as the nuclei approach one another the g orbitals become bonding and the u orbitals antibonding. Furthermore, the two former have the same irreducible representation ag) in Doo/i, so - from the considerations outlined in Section 2.2.6 - they should mix, as should the two antibonding a orbitals, one of each pair being stabilized and the other destabilized. ... 

To further illustrate these points dealing with orbital symmetry, consider the insertion of CO into H2 along a path which preserves C2v symmetry. As the insertion occurs, the degenerate n bonding orbitals of CO become hi and 62 orbitals. The antibonding n orbitals of CO also become hi and 62. The <5g bonding orbital of H2 becomes ai, and the antibonding H2 orbital becomes 62. The orbitals of the reactant... 

Figure 15.3 The six benzene tt molecular orbitals. The bonding orbitals >p2 and t 3 have the same energy and are said to be degenerate, as are the antibonding orbitals tf/4 and 5. The orbitals and 4 have no tt electron density on two carbons because of a node passing through these atoms.

Fig. 1 A schematic illustration of the in-phase and out-of-phase combinations of the atomic orbitals into the bonding and antibonding molecular orbitals, respectively. The dissociation limit of a H molecule corresponds to a pure diradical with degenerate singlet and triplet states...

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