Strength of Orbital Interactions

There are many occupied and unoccupied molecular orbitals in molecules. Interactions occur between any pair of the molecular orbitals. The strengths of the interactions and the effects on the energies of interacting molecules are different from each other. Some lead to significant stabihzation or destabihzation, others to only slight stabihzation or destabilization. 

Chapters 6-11 describe applications of orbital interaction theory to various chemical systems in order to show how familiar concepts such as acid and base strengths, nucleo-... 

The energy level diagram we wish to construct will show how the energies of the various states into which the free-ion terms are split depend on the strength of the interaction of the ion with its environment. The separation of the two sets of orbitals into which the group of five d orbitals is split can be taken as our measure of this interaction. Thus our diagram will have the... 

The interaction of C-M bonding orbitals with heteroatom lone-pair orbitals is a two-center-four-electron interaction. This is destabilizing and raises the energy of the HOMO relative to the unperturbed orbitals, and hence lowers the ionization potential of the heteroatom lone-pair electrons. The interaction is qualitatively represented by the molecular orbital interaction diagram shown in Figure 11. The strength of the interactions depends on a number of factors but most importantly on the orientation of the C-M bond with respect to the lone-pair orbital and on the... 

All enamine systems involve a resonance interaction between the lone pair of the nitrogen atom and the n orbital of the ethylene system which is obviously influenced by the presence of substituents whose effect is especially marked if the structural alteration results in the loss of planarity of the enamine system. It would thus be of interest to develop a quantitative index for the strength of such interaction. One such index could be the difference between the ionization potentials assigned to the fragments, which will increase with the increase in the resonance between them. In principle, they could indeed be linearly related. 

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