Free-electron model highest occupied molecular orbital

In the four-orbital model (1 ), low-lying ir-ir states of free-base porphyrins (symmetry D2h) are considered as resulting from single electron excitation from a pair of nondegenerate highest occupied molecular orbitals (bi, bo) to a pair of nondegenerate lowest unoccupied molecular orbitals (ci, cg). In the case of symmetry D2h mutually perpendicular electric transition dipoles X and Y are not equivalent and, therefore, in the visible absorption spectra of free-base porphyrins two different electronic bands Qx(0>0) and Qy(0,0) are observed (Table 1 and Fig. 10). 

Table XII summarizes HMO quantities referring to models of sulfur compounds total 7r-electronic energy (W7), energies of the two highest occupied molecular orbitals (k2 and ky kx is referred to as HOMO in the text), energies of the two lowest free molecular orbitals (k-x and k 2 k-i is referred to as LFMO in the text), and the energy...

The free-electron model can also be applied to the electronic spectrum of butadiene and other linear polyenes. The lowest unoccupied molecular orbital (LUMO) in butadiene corresponds to the = 3 particle-in-a-box state. Neglecting electron-electron interaction, the longest-wavelength (lowest-energy) electronic transition should occur from n — 2, the highest occupied molecular orbital (HOMO), as shown below ... 

Highest occupied molecular orbital free-electron model, 38-39 geometry and stereoselectivity of reactions, 175-177 Hilbert space, definition, 53 Hohenberg-Kohn theorem, 189-190 HOMO, see Highest occupied molecular orbital... 

The combination of quantum mechanical calculations and the linear free-energy related model has been used recently by several investigators in drug activity studies—i.e., a variety of indices obtained from the quantum chemical calculations has been utilized in these correlations (4, 8, 114). For example, Neely and co-workers obtained excellent correlations between the energy of the highest occupied molecular orbital, a relative measure of the ability of a molecule to donate an electron to an acceptor molecule, of a series of imidazolines and their analgetic potencies (115). 

H2, N2, or CO dissociates on a surface, we need to take two orbitals of the molecule into account, the highest occupied and the lowest unoccupied molecular orbital (the HOMO and LUMO of the so-called frontier orbital concept). Let us take a simple case to start with the molecule A2 with occupied bonding level a and unoccupied anti-bonding level a. We use jellium as the substrate metal and discuss the chemisorption of A2 in the resonant level model. What happens is that the two levels broaden because of the rather weak interaction with the free electron cloud of the metal. 

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