Highest energy occupied orbitals

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.

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 ... 

A Which is larger, Na or E Eor each of these ions, draw a representation of the shape of the highest energy occupied orbital. 

The term molecule means here a species that possesses, on the highest energy occupied orbital, two electrons, in contrast to a radical. The charge on system is null in molecules and different from zero in molecular ions. Radicals are not analyzed here, but some molecular ions are analyzed. 

The orbitals must also have a similar energy. For the greatest interaction, the two orbitals should have the same energy. Only the highest-energy occupied orbitals (or HOMOs) of the nucleophile are likely to be similar in energy to only the lowest-energy unoccupied orbitals (or LUMOs) of the electrophile. 

HOMO stands for highest energy occupied orbital... 

Because the molecular orbital vj/j of Eqn. (8) is N-O antibonding (cf Eqm (7-5)), it is the highest-energy occupied orbital of T, (MO). When two electrons are excited from Vj into the vacant molecular orbital of Eqn. (7-6), (which is both N-0 and N-N antibonding), the lowest-energy doubly-excited configuration (MO) of Eqn. (16) is obtained. 

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