Lowest Occupied Molecular Orbital LUMO

The stereochemical outcome of the reaction was rationalized by invoking axial approach of the alkene lowest occupied molecular orbital (LUMO) to the least hindered lower face of the highest occupied molecular orbital (HOMO) of the dipole, in which the morpholinone ring was held in a quasi-chair conformation with the C(5) phenyl substiment in an equatorial environment (Fig. 3.13). 

The observed femtosecond dynamics of this dissociative CT reaction is related to the nature of bonding. Upon excitation to the CT state, an electron in the highest occupied molecular orbital (HOMO) of benzene (ir) is promoted to the lowest occupied molecular orbital (LUMO) of I2 (a ). Vertical electron attachment of ground state I2 is expected to produce molecular iodine anions in some high vibrational levels below the dissociation limit. In other words, after the electron transfer, the I—I bond is weakened but not yet broken. While vibrating, the entire I2 and benzene complex begins an excursion motion within die coulombic field and the system proceeds... 

Figure 3. Overlap of the lowest occupied molecular orbital (LUMO) of the oxidant—the n orbital of NO —with the highest occupied molecular orbital (HOMO) of the reductant—the orbital of...

CMR (10) and ultraviolet (UV). The interaction in a CT complex is considered to involve an electron transfer from the highest occupied molecular orbital (HOMO) of an electron donating comonomer to the lowest occupied molecular orbital (LUMO) of an electron accepting comonomer (11). This electron transfer results in a new absorption in UV, a characteristic of the CT complex. 

Similarly, for eleetronie affinity, one will act on the in se quantum system to add an eleetron at the frontier level and, under the frozen spin-orbitals physical-chemieal assumption, one gets the energetic turn from the genuine HF expression to the in silico orbital energy on which the action was imdertaken towards the first lowest occupied molecular orbital (LUMO), see Figure 4.3 ... 

Depending on the positions of the highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) of the dye, the photoexcited state may inject either electrons or holes into the conduction or valence band, respectively, of the solid [7] as shown in Fig. 1. (Note the broken arrows in Fig. 1 which show the direction in which electrons move). 

This work cast valuable light on these systems, as UV-vis spectroscopic analysis clearly identified a charge-transfer band centered at = 319 nm for 4b, for example, and excitation at this wavelength led to emission at Xeni = 480nm (Figure 15.3). Semiempirical (MNDO) calculations established that the highest occupied molecular orbital (HOMO) was primarily localized on the boron cage cluster, while the lowest occupied molecular orbital (LUMO) was mostly concentrated... 

In view of this, early quantum mechanical approximations still merit interest, as they can provide quantitative data that can be correlated with observations on chemical reactivity. One of the most successful methods for explaining the course of chemical reactions is frontier molecular orbital (FMO) theory [5]. The course of a chemical reaction is rationali2ed on the basis of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), the frontier orbitals. Both the energy and the orbital coefficients of the HOMO and LUMO of the reactants are taken into account. 

If the mini her of electrons, N, is even, yon can haven dosed shell (as shown ) where the occupied orbitals each contain two electron s. For an odd n nrn her of electron s, at least on e orbital rn ust be singly occupied. In the example, three orbitals are occupied by-electron s and two orbitals arc nn occupied. Th e h ighest occupied nioleciilar orbital (HOMO is t[r), and the lowest unoccupied molecular orbital (LUMO) is The example above is a singlet, a state oh total spin S=0. Exciting one electron from the HOMO to the LUMO orbital would give one ol the I ollowing excited states ... 

I he electron density distribution of individual molecular orbitals may also be determined and plotted. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are often of particular interest as these are the orbitals most cimimonly involved in chemical reactions. As an illustration, the HOMO and LUMO for Jonnamide are displayed in Figures 2.12 and 2.13 (colour plate section) as surface pictures. 

When you request an orbital, you can use the cardinal number of the orbital (ordered by energy and starting with number=l) or an offset from either the highest occupied molecular orbital (HOMO) or the lowest unoccupied molecular orbital (LUMO). Offset from the HOMO are negative and from the LUMO are positive. Often these frontier orbitals are the ones of most chemical interest. 

Thermodynamic properties such as heats of reaction and heats of formation can be computed mote rehably by ab initio theory than by semiempirical MO methods (55). However, the Hterature of the method appropriate to the study should be carefully checked before a technique is selected. Finally, the role of computer graphics in evaluating quantum mechanical properties should not be overlooked. As seen in Figures 2—6, significant information can be conveyed with stick models or various surfaces with charge properties mapped onto them. Additionally, information about orbitals, such as the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), which ate important sites of reactivity in electrophilic and nucleophilic reactions, can be plotted readily. Figure 7 shows representations of the HOMO and LUMO, respectively, for the antiulcer dmg Zantac. 

Fig. 7. Graphical representations of (a) the Highest Occupied Molecular Orbital (HOMO) and (b) the Lowest Unoccupied Molecular Orbital (LUMO) for ranitidine. It is possible, in the ordinarily visible color-coded data not shown here, to distinguish the strong localization (a) of the HOMO to the sulfur atom and adjacent nitroethyleneamine fragment and the contrasting localization (b) of the LUMO to the nitroethylenearnine fragment. Neither the LUMO not HOMO appear to have contributions from the dimethylaminomethyl-suhstitiited furan.

It is now possible to "see" the spatial nature of molecular orbitals (10). This information has always been available in the voluminous output from quantum mechanics programs, but it can be discerned much more rapidly when presented in visual form. Chemical reactivity is often governed by the nature of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Spectroscopic phenomena usually depend on the HOMO and higher energy unoccupied states, all of which can be displayed and examined in detail. 

The most extensive calculations of the electronic structure of fullerenes so far have been done for Ceo- Representative results for the energy levels of the free Ceo molecule are shown in Fig. 5(a) [60]. Because of the molecular nature of solid C o, the electronic structure for the solid phase is expected to be closely related to that of the free molecule [61]. An LDA calculation for the crystalline phase is shown in Fig. 5(b) for the energy bands derived from the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) for Cgo, and the band gap between the LUMO and HOMO-derived energy bands is shown on the figure. The LDA calculations are one-electron treatments which tend to underestimate the actual bandgap. Nevertheless, such calculations are widely used in the fullerene literature to provide physical insights about many of the physical properties. 

Dimethylborane+propene Cl depicts the transition state for addition of dimethylborane onto the terminal alkene carbon of propene. Examine and describe the vibration with the imaginary frequency. Which bonds stretch and compress the most What simultaneous changes in bonding are implied by these motions Simultaneously display the highest-occupied molecular orbital (HOMO) of propene and the lowest-unoccupied molecular orbital (LUMO) of dimethylborane. Is the overall geometry of the transition state consistent with constructive overlap between the two Explain. 

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