Orbitals, antibonding overlap

FIGURE 3.30 Two p-orbitals can overlap side by side to give bonding (below) and antibonding (above) u-orbitals. Note that the latter has a nodal plane between the two nuclei. Both orbitals have a nodal plane through the two nuclei and look like p-orbitals when viewed along the internuclear axis. 

Because the H-end of the cta i i antibond encloses no electronic core, the incoming ns donor orbital can overlap with practically the entire hydride end of the antibond, rather than merely the outer annular region that lies beyond the nodal boundary of the core region. 

In Fig. 7.3 the d bands are shown split into sub-bands. The lower d bands are derived from the d orbitals that overlap least with the chalcogen p orbitals. (This is because the d bands are formed from antibonding combinations of d and p orbitals, and those with more overlap are pushed higher in energy.) The details of the splitting depend on how the... 

These orbitals completely overlap with two Si-C antibonding orbitals, since the antibonding orbitals are expressed by... 

Finally, we turn to the MOs formed by the 12 tangential (px and py) orbitals. For the type we already have the shapes from our discussion of the n bonding in an octahedral AB6 molecule. The others can be obtained by use of projection operators, and one representative of each set is shown in Figure 8.16. For these orbitals the overlaps implied by these drawings show that the and the Tlu sets are bonding and the T g and 7 antibonding. 

Figure 6-6 (a) Schematic representation of formation of bonding (molecular orbitals by overlap of two atomic 1s orbitals, (b) Some of the various electronic configurations that are possible with these orbitals... 

In the anti conformation, the second electron pair on the oxygen atom (cf. 49 and 51 ) is oriented anti peri planar to the polar C—N bond, so this electron pair orbital can overlap with the antibonding orbital (o ) of the C —N sigma bond. Thus, contrary to the syn isomer, anti imidates have in addition to the primary electronic effect, one secondary electronic effect (n-o ). This additional electronic delocalization should stabilize the anti form relative to the syn form. 

If a cycloaddition produces an overlap of positive-phase orbitals with negative-phase orbitals (destructive overlap), antibonding interactions are generated. Antibonding interactions raise the activation energy, so the reaction is classified as symmetry-forbidden. The thermal [2 + 2] cycloaddition of two ethylenes to give cyclobutane is a symmetry-forbidden reaction. 

An overlap of orbitals that contributes to antibonding. Overlap of lobes with opposite phases (+ phase with — phase) is generally destructive overlap, (p. 671)... 

We can also explain inversion of configuration in the Sn2 reaction by looking at the frontier orbitals, but it is a much weaker explanation. The appropriate frontier orbitals will be the HOMO of the nucleophile and the LUMO of the electrophile. Taking the orbitals of methyl chloride in Figs 1.45 and 1.47, we can see the LUMO is the [Pg.155]

MOs of ethene The carbon atoms in ethene are sp hybridized. The double bond between two carbon atoms comprises a a- and a ir-bond. The carbon-carbon a-bond is formed by the head-on overlap of two sp -orbitals. The overlapping results in two MOs a bonding (ct) and an antibonding (ct ). The TT-bond is formed by the side-on overlap of p-orbitals. The bonding orbital is formed by the overlap of in-phase p-orbitals, and the antibonding orbital arises from the interference between two p-orbitals of opposite phases and has a node (or a region of minimum electron density between the nuclei). These orbitals are designated as TV and 77, respectively (Fig. 8.5). 

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