Highest occupied molecular orbital analysis

CH3I should approach the enolate from the direction that simultaneously allows its optimum overlap with the electron-donor orbital on the enolate (this is the highest-occupied molecular orbital or HOMO), and minimizes its steric repulsion with the enolate. Examine the HOMO of enolate A. Is it more heavily concentrated on the same side of the six-membered ring as the bridgehead methyl group, on the opposite side, or is it equally concentrated on the two sides A map of the HOMO on the electron density surface (a HOMO map ) provides a clearer indication, as this also provides a measure of steric requirements. Identify the direction of attack that maximizes orbital overlap and minimizes steric repulsion, and predict the major product of each reaction. Do your predictions agree with the thermodynamic preferences Repeat your analysis for enolate B, leading to product B1 nd product B2. 

The Woodward-Hoffmann rules for pericyclic reactions require an analysis of all reactant and product molecular orbitals, but Kenichi Fukui at Kyoto Imperial University in Japan introduced a simplified version. According to Fukui, we need to consider only two molecular orbitals, called the frontier orbitals. These frontier orbitals are the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). In ground-state 1,3,5-hexa-triene, for example, 1//3 is the HOMO and excited-stale 1,3,5-hexatriene, however, 5 is the LUMO. 

An analogous picture is drawn for analysis of XA in Fig. 4B. It should be remembered that the highest occupied molecular orbital of the xanthylidene-substituent is the lowest unoccupied orbital for the BA system. Interaction of this occupied aryl orbital with those of the prototype carbene gives the orbitals of XA shown in the center of Fig. 4B. The energy... 

Each reaction species must have molecular orbitals available and with the correct symmetry to allow bonding. These will be called frontier orbitals composed of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). In addition to their involvement in bonding between species, these orbitals are of considerable interest in that they are largely responsible for many of the chemical and spectroscopic characteristics of molecules and species and are thus important in analytical procedures and spectroscopic methods of analysis [5-7],... 

Molecular orbital calculations have been performed on compounds 19 and 20 . The calculated PM3 equilibrium geometric structures show that these compounds are severely distorted from planarity in accordance with X-ray structural analysis (see Section 8.I2.3.I). On the other hand, PM3 calculations performed on both neutral and oxidized/reduced compounds show that oxidation and reduction induce a clear gain of aromaticity. Predictions using the nonempirical valence effective Hamiltonian (VEH) method have shown that the electronic charge density in the highest occupied molecular orbital (HOMO) is localized on the benzodithiin 19 or benzoxathiin 20 rings. 

In recent years, molecular descriptors such as the energy of the highest occupied molecular orbital (EHomo) ar d the energy of the lowest unoccupied molecular orbital ( IUMO) have gained in popularity for QSAR analysis, as these descriptors are readily calculated from PC-based software such as SPARTAN. Before we discuss EHomo ar d ELumo further, a brief discussion of quantum chemistry is necessary. 

Theoretical analysis of this [4% + 27r]-cycloaddition reaction by consideration of frontier-orbital interactions between the electron-rich olefin (highest occupied molecular orbital, HOMO) and the electron-poor 5-nitropyrimidine (LUMO) has shown that the FMO perturbation theory correctly predicts an exclusive regiospecific addition of the enamine to N-l and C-4 of the pyrimidine ring (86JOC4070). 

The nature of the frontier orbitals is also of interest and a Mulliken population analysis of the constituent orbitals establishes that the highest occupied molecular orbital (HOMO) of each phosphine consists primarily of a lone pair sp hybrid on phosphorus. The orbital energy ordering PMe3 < PH3 < PF3 also parallels the percentage phosphorus s-character of the HOMO of PMe3 (11% s and 60% p), PH3 (14% s, 67% p) and PF3 (29% s, 32% p). In each case the back lobe of the sp hybrid interacts with the substituent attached to phosphorus in a (T-bonding fashion. 

ADE = adiabatic detachment energies ESC A = electron spectroscopy for chemical analysis HOMO = highest occupied molecular orbitals MAES = metastable atom electron spectroscopy MIES = metastable ionization electron spectroscopy OAT = oxygen atom transfer PES = photoelectron spectra PEI = pulsed field ionization PIES = Penning ionization electron spectroscopy QM = quantum-mechanical REMPI = resonantly enhanced multiphoton ionization SC = semiclassical VDE = vertical detachment energies XPS = x-ray photoelectron spectroscopy ZEKE = zero electron kinetic energy Cp = cyclopentadienyl, Ph = phenyl, CeHs Tp =... 

Mxdliken population analysis was used for the evaluation of the net charge of each atom and the bond overlap populations of each cluster. The Fermi energy Ep of each cluster was evaluated as the midpoint of the energy gap between the highest occupied molecular orbital (HOMO) and the lowest xmoccupied molecular orbital (LUMO). In order to discuss the bonding nature, we used the familiar chemist s bond order which is the sum of the bond overlap populations between each pair of atoms in the cluster. 

Cycloadditions are controlled by orbital symmetry (Woodward-Hoffman rules) and can take place only if the symmetry of all reactant molecular orbitals is the same as the symmetry of the product molecular orbitals. Thus, an analysis of all reactant and product orbitals is required. A useful simplification is to consider only the frontier molecular orbitals. These orbitals are the highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO). The orbital symmetry must be such that bonding overlap of the terminal lobes can occur with suprafacial geometry that is, both new bonds are formed using the same face of the diene. 

The ionization potential in a simple one-electron approximation measures the energy of the highest occupied molecular orbital (HOMO). This orbital is only one of an entire manifold of levels which contribute to the bonding characteristics and total stability of the cluster. Frontier fragment-orbital analysis in organometallic reactivity studies has provided a clear indication... 

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