HOMO-LUMO diagrams

FIGURE 6-12 HOMO-LUMO Diagrams for Hard-Hard and Soft-Soft Interactions. (Adapted with permission from W. B. Jensen, The Lewis Acid-Base Concepts, Wiley-fnterscience, New York, 1980, pp. 262-263. Copyright 1980, John Wiley Sons, Inc. Reprinted by permission of John Wiley Sons, Inc.)... 

Figure 11.11. The HOMO-LUMO diagram for protonated acroiein. [Reprinted with permission from Fleming, l. Frontier Molecular Orbitals and Organic Chemical Reactions, Wiley, London, 1976, pp. 163. Copyright 1976 by John Wiley and Sons, Inc.]...

Figure 1. Hiickel n-MO correlation diagrams for planar- perp twisting of pcntamethine cyanine about the 2-3 and 3-4 bonds (a), and simultaneous twisting about 2-3 and 4-5 bonds (b). For the perp forms the orbitals belonging to the different n fragments are indicated and the CT nature of the HOMO-LUMO excitation is emphasized.

FIGURE 3.4 Molecular level alignment diagrams constructed using the HOMO and vacuum levels measured using UPS. The lowest unoccupied molecular orbital LUMO positions are inferred assuming a HOMO/LUMO gap equal to the onset of optical absorption. The chemical structure of CuPc is shown. (From Hill, I.G. and Kahn, A., J. Appl. Phys., 86, 2116, 1991. With permission.)... 

The solvent effect on the azo-hydrazone equilibrium of 4-phenylazo-l-naphthol has been modelled using ab initio quantum-chemical calculations. The hydrazone form is more stable in water and in methylene chloride, whereas methanol and iso-octane stabilise the azo form, The calculated results were in good agreement with the experimental data in these solvents. Similar studies of l-phenylazo-2-naphthol and 2-phenylazo-l-naphthol provided confirmation. Substituent effects in the phenyl ring were rationalised in terms of the HOMO-LUMO orbital diagrams of both tautomeric forms [53]. 

The interaction diagram for the cis and trans union of two FHC radical fragments is shown in Fig. 38. From Fig. 38 it is obvious that the pi HOMO-LUMO splitting is larger for the case of cis union than for trans union. The final conclusions is that the HOMO and LUMO energies in cis and trans 1,2-difluoroethylene vary in the following way ... 

Fig. 6 (a) Cyclic voltammograms Cgo (top) and Sc3N / ,-C8o (bottom) in a 0.050 M solution of TBAPFg in o-DCB. (b) Schematic energy diagram of HOMO-LUMO gaps difference between Cgo and Sc3N 4-Cgo... 

Orbital Interaction Analysis. An orbital interaction diagram for the Diels-Alder reaction is shown in Figure 12.5a. The geometry of approach of the two reagents which ensures a maximum favorable interaction between the frontier MOs (dashed lines) preserves a plane of symmetry at all separations. The MOs are labeled according to whether they are symmetric (S) or antisymmetric (A) with respect to reflection in the plane. Simultaneous overlap of both HOMO-LUMO pairs is a necessary feature of all peri-... 

The essential features of the Diels-Alder reaction are a four-electron n system and a two-electron it system which interact by a HOMO-LUMO interaction. The Diels-Alder reaction uses a conjugated diene as the four-electron n system and a it bond between two elements as the two-electron component. However, other four-electron it systems could potentially interact widi olefins in a similar fashion to give cycloaddition products. For example, an allyl anion is a four-electron it system whose orbital diagram is shown below. The symmetry of the allyl anion nonbonding HOMO matches that of the olefin LUMO (as does the olefin HOMO and the allyl anion LUMO) thus effective overlap is possible and cycloaddition is allowed. The HOMO-LUMO energy gap determines the rate of reaction, which happens to be relatively slow in this case. 

Fig. 1 Schematic molecular orbital diagram showing the effect of aurophilic contacts on the HOMO-LUMO energy gap of gold(I) phosphine complexes...

Fig. 10 Molecular orbital energy diagram of complexes 2, 18, and 20 compared to that of a Ti02 nanoparticle model. HOMO-LUMO gaps (eV) and lowest TDDFT excitation energies (eV, data in parenthesis) are reported together with isodensity plots of the HOMO-3, HOMO, and LUMO of complex 20...

Figure 4 Electronic energy level diagram for Pbn, n = 3 — 14. Degeneracies are indicated by a number attached to the level. A vertical bar indicates the HOMO-LUMO gap.

Fig. 1. HOMO - LUMO interaction diagram for MR3 radicals. (A) Interaction of a singly occupied p orbital (HOMO) with the a (LUMO) of planar MR3 that results in stabilization of the HOMO on pyramidalization. (B) Superposition of the HOMO and LUMO from (A). Arrows show the distortion that results in a stabilizing interaction.

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