Orbital lowest unoccupied

AMI semi-empirical and B3LYP/6-31G(d)/AMl density functional theory (DFT) computational studies were performed with the purpose of determining which variously substituted 1,3,4-oxadiazoles would participate in Diels-Alder reactions as dienes and under what conditions. Also, bond orders for 1,3,4-oxadiazole and its 2,5-diacetyl, 2,5-dimethyl, 2,5-di(trifluoromethyl), and 2,5-di(methoxycarbonyl) derivatives were calculated <1998JMT153>. The AMI method was also used to evaluate the electronic properties of 2,5-bis[5-(4,5,6,7-tetrahydrobenzo[A thien-2-yl)thien-2-yl]-l,3,4-oxadiazole 8. The experimentally determined redox potentials were compared with the calculated highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) energies. The performance of the available parameters from AMI was verified with other semi-empirical calculations (PM3, MNDO) as well as by ab initio methods <1998CEJ2211>. 

In accordance with theoretical predictions (90), the concerted pathway for 1,3-dipolar cycloaddition is replaced by a two-step mechanism when two requirements are satisfied. One of the criteria involves an extremely large difference in the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energies of the reaction partners. The other factor involves a pronounced steric hindrance at one termini of the 1,3-dipole (190). The first case of a stepwise... 

We may redraw 6 as 7a and 7b, in terms of frontier MOs. Here we emphasize the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) interactions that operate in the transition state 7a depicts the LUMO(carbene)/HOMO(alkene) or p-n interaction 7b shows the HOMO (carbene)/LUMO(alkene) or a-71 interaction. These formulations are especially... 

Puddephatt and co-workers (153, 154) reported a novel use of a calixresor-cinarene for anion binding. Receptor 61 was synthesized and tetracopper(I) and tetrasilver(I) complexes were isolated. In each case, an electron deficient cavity is formed with an array of four metal ions around its upper rim. These metal ions are capable of coordinating an anion between them. Crystal structures [Fig. l(a and b) of two such anion inclusion complexes were resolved and a discussion of highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) overlap was provided. The nature of the cavity was shown to... 

With the progress in the chemical calculation of the molecule, analyses with HOMO/LUMO (highest occupied molecular orbital/lowest unoccupied molecular orbital) energy, absolute hardness/absolute electron negativity, and research into these new and old descriptors have been reported recently. Furthermore, new methods with neural network computers, as well as multiregression analysis, cluster analysis, and major component analysis have been applied to investigate the relationship between the property and function of the molecule and of each descriptor. 

El.30 Frontier orbitals of Be Recall from Section 1.9(c) Electron affinity, that the frontier orbitals are the highest occupied and the lowest unoccupied orbitals of a chemical species (atom, molecule, or ion). Since the ground-state electron configuration of a beryllium atom is ls 2s , the frontier orbitals are the 2s orbital (highest occupied) and three 2p orbitals (lowest unoccupied). Note that there can be more than two frontier orbitals if either the highest occupied and/or lowest unoccupied energy levels are degenerate. In the case of beryllium we have four frontier orbitals (one 2s and three 2p). 

James McFarland (to William Purcell) There is an air of mysticism in the use of molecular orbital parameters. Do you feel that these parameters relate to biological processes that we are already familiar with or do they perhaps relate to something we don t yet understand about how drugs act If it is the former, would you elaborate on how we might interpret successful correlations with such terms as highest occupied molecular orbital, lowest unoccupied molecular orbital, and frontier orbital ... 

Boron Tetraalkoxydiboranes, activated by a Lewis base, generate a nucleophilic sjp-carbene-type boryl moiety that can attack non-activated C=C bonds. Computational studies identified the interaction as the overlap of the strongly polarized B—B a bond (highest occupied molecular orbital, HOMO) with the tt orbital (lowest unoccupied molecular orbital, LUMO) of the C=C bond. According to this scenario, the normally electrophilic boron becomes nucleophilic and forces the olefin to act as an electrophile. ... 

It is important to note that many metallic properties, such as the Knight shift and the Korringa relationship, are determined by the finite and quasiFermi level local density of states ( p-LDOS). In the approximation most familiar to chemists, what this means is that the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap in metals is much smaller than the thermal energy kf,T, and the value of the / f-LDOS reflects the frontier orbital contributions in a metallic system [23]. The /ip-LDOS also represents a crucial metal sxudace attribute that can serve as an important conceptual bridge between the delocalized band structure (physics) picture and the localized chemical bonding (chemical) picture of metal-adsorbate interactions. 

Solute ability to accept or donate hydrogen in a hydrogen bond Highest Occupied Molecular Orbital Lowest Unoccupied Molecular Orbital Electronegativity of HOMO state for ELH (hydrogen)... 

Reactions such as these that involve polar molecules are best understood in terms of Highest Occupied Molecular Orbital—Lowest Unoccupied Molecular Orbital (HOMO-LUMO) orbital interactions. As we saw in Section 1.7, p. 41, when a filled occupied orbital overlaps an empty orbital, the two electrons are stabilized in the new, lower energy molecular orbital. The words Lewis bases react with Lewis acids are essentially equivalent to saying, The interaction of a filled and empty orbital is stabilizing. Indeed, this notion is one of the central unifying themes of organic reactivity, as essentially all reactions involving polar molecules can be understood this way. 

---