Highest-occupied energy

The most important molecular- orbitals are the so-called frontier molecular- orbitals. These are the highest (energy) occupied molecular- orbital (HOMO), and lowest (energy) unoccupied molecular- orbital (LUMO). The following picture shows the LUMO surface for the hydrogen molecule, H2. The LUMO consists of two separate surfaces, a red... 

The highest-energy occupied molecular orbital (HOMO) and the lowest-energy unoccupied molecular orbital (LUMO) of a particular molecular entity. The HOMO can be completely or partially filled whereas the LUMO can be completely or partially vacant. The frontier orbital method allows one to interpret reaction behavior by studying HOMO and LUMO overlaps between reacting entities. 

Lever has successfully predicted Mn"/ potentials of 24 Mn-carbonyl complexes containing halide, pseudohalide, isonitrile, and phosphine co-ligands, with additivity parameters derived from the potentials of Ru "/" couples [39]. An important consideration for heteroleptic complexes is the influence of isomerism on redox thermodynamics. For Mn(CO) (CNR)6- complexes, with n = 2 or 3, the Mn"/ potentials for cis/trans and fac/mer pairs differ by as much as 0.2 V [40]. The effect arises from the different a-donor and 7r-acceptor abilities of carbonyl (CO) and isocyanide and their influence on the energy of the highest energy occupied molecular orbital (HOMO). 

The reduction of DMSO catalyzed by molybdenum is an important step in the process of anaerobic respiration carried out by a number of bacteria (169). Much like sulfite oxidase, early MCD studies of DMSO reductase were complicated by the presence of heme iron (173). The discovery of two enzymes that do not include an iron center led to the measurement of MCD spectra of Rhodobacter sphaeroides DMSO reductase that could be assigned exclusively in terms of transitions of the Mo site (Fig. 10b) (174). The six major peaks are assigned as LMCT transitions from the three highest energy occupied orbitals to the two lowest unoccupied orbitals (174). 

Figure 8. Interaction of the three highest energy occupied orbitals of dimethylsulfide with copper. Top shifts in energies relative to the sulfur 2s orbital. Bottom character of the orbitals in terms of atomic orbitals. Primed coordinates of the copper-bound sulfur p orbitals indicate a ligand-based coordinate system. Reproduced from Ref. 14. Copyright 1985, American Chemical Society.

The distribution of -electrons over the tt-MOs is regulated by the Aufbau principle and the Pauli rule. The highest energy occupied MO thereof is called the HOMO (highest occupied molecular orbital). The lowest unoccupied MO thereof is called the LUMO (lowest unoccu-... 

Excitation in general consists in promotion of an electron from one of the highest-energy occupied molecular orbitals (HOMOs) to achieve one of the lowest-energy unoccupied molecular orbitals (LUMOs) of the ground-state molecule. This may be expressed, for example, by the terms (n, 7i ), (n, a ), (n, tt ), or (n, a ), whereas the multiplicity is shown as a prefix, eg 1(n, if ). Population of the antibonding excited states thus usually results in bond weakening. 

One can define the Fermi energy ef as the highest energy occupied in the band ... 

Figure 4. The four highest energy occupied MOs of the ethene-l,2-dithiolate (edt2-) ligand as determined by ab initio and DFT calculations. Note that both in-plane and out-of-plane orbitals are present.

Fig. 4.27. Molecular-orbital energy-level diagram for the (FeO,) " cluster calculated using the MS-SCF-Jfa method. The highest-energy occupied orbital is the 2 2g i containing one electron. Also shown are the energies of Fe and O atomic orbitals. Spin-up (f ) and spin-down ( i ) molecular orbitals are shown in this spin-unrestricted calculation on a regular octahedral (O ) cluster at an iron-oxygen distance of 2.17 A (after Tossell et al., 1974 reproduced with the publisher s permission).

The azide ion, N3, is another linear triatomic species. Calculate and display the orbitals for this ion and compare the three highest energy occupied orbitals with those of Bep2. How do the outer atom group orbitals differ in their interactions with the central atom orbitals How do the orbitals compare with the CO2 orbitals ... 

The usual ab initio Hartree-Fock computations lead to the canonical orbitals which allow a simple assignment of an energy quantity ("orbital energy") to each orbital. In particular, the contour surfaces of the highest (highest-energy) occupied (HOMO) and lowest unoccupied (LUMO) orbitals, and the frontier orbitals [96,97] are often used to interpret properties of molecules and reactions. 

HOMO highest energy occupied molecular orbital KDO 3-deoxy-D-ma o-2-octulosonic acid... 

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