Orbital highest filled

An alternative approach is in terms of frontier electron densities. In electrophilic substitution, the frontier electron density is taken as the electron density in the highest filled MO. In nucleophilic substitution the frontier orbital is taken as the lowest vacant MO the frontier electron density at a carbon atom is then the electron density that would be present in this MO if it were occupied by two electrons. Both electrophilic and nucleophilic substitution thus occur at the carbon atom with the greatest appropriate frontier electron density. 

Another aspect of qualitative application of MO theory is the analysis of interactions of the orbitals in reacting molecules. As molecules approach one another and reaction proceeds, there is a mutual perturbation of the orbitals. This process continues until the reaction is complete and the new product (or intermediate in a multistep reaction) is formed. PMO theory incorporates the concept of frontier orbital control. This concept proposes that the most important interactions will be between a particular pair of orbitals. These orbitals are the highest filled oihital of one reactant (the HOMO, highest occupied molecular oihital) and the lowest unfilled (LUMO, lowest unoccupied molecular oihital) orbital of the other reactant. The basis for concentrating attention on these two orbitals is that they will be the closest in energy of the interacting orbitals. A basic postulate of PMO... 

With the oxide semiconductors, anionic chemisorption would take place over the metal cations, and the interaction problem would be between the orbitals on the foreign atom and the cation band (the 3d band in CU2O, for example). The discussion in this section is relevant if this is the highest filled band. 

With the semiconducting oxides, we expect anionic chemisorption to occur over the lattice cations, and our simple molecular orbital theory will be adequate if the conduction band is associated mainly with the cation lattice. This is certainly the case with AI2O3, where there is direct evidence in the soft X-ray emission spectra that the highest filled band is the oxygen 2p band 16). 

Finally, we note that if the interaction problem is between the orbital on the foreign atom and the highest filled band of the solid, anionic chemisorption is found in all regions of the diagram in Fig. 7, provided only that the highest localized level falls below the impurity levels in the solid. 

The Coulomb terms of the arene orbitals are obtained by equating the observed first ionization potential of benzene with the Coulomb term of the highest filled orbital ... 

This band arises due to the transition of an electron from the molecule with high charge density (donor) to the molecule with low charge density (acceptor). The transition occurs from the highest filled olecular orbital of the donor to the lowest empty molecular orbital of he acceptor. Promotion of an electron to higher unoccupied orbitals of the acceptor... 

Intensification of the 7F0 - 5D0j 7F0 - sDi and 7Fo bLi bands in the somewhat unstable Eu3+-diethyldithiocarbamate has been reported by J0RGENSEN 592. He has also observed genuine electron transfer bands from the highest filled molecular orbital to the partly filled 4/ shell in the bromo complexes of Nd3+, Sm3+, Eu3+, Tm3+ and Yb3+. In the case of Eu3+ the electron transfer bands occur [592] at 3200, 2660 and 2300 A corresponding to 31250, 37594 and 43478 cm-1 respectively. 

In order to understand this process, the nature of the Fermi level must be considered. Within the nomenclature of physics, the Fermi level is defined as the energy at which there is a 50% probability of finding an electron in a metal— what a chemist would call the highest filled molecular orbital (i.e., the top of the valence band). In an intrinsic semiconductor, a material having a completely filled valence band and a completely empty conduction band, this energy level... 

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