LUMO orbital energies

Quantum chemical descriptors such as atomic charges, HOMO and LUMO energies, HOMO and LUMO orbital energy differences, atom-atom polarizabilities, super-delocalizabilities, molecular polarizabilities, dipole moments, and energies sucb as the beat of formation, ionization potential, electron affinity, and energy of protonation are applicable in QSAR/QSPR studies. A review is given by Karelson et al. [45]. 

Figure 7. HOMO and LUMO orbital energies for C0 2Hg, plotted vs 1/N.

The HOMO and LUMO orbital energies seem to converge towards a value of about 4 eV, which would be an estimate of the work function for single sheet graphite. This is in reasonable agreement with the work function of 4.9 eV experimentally found for bulk graphite(58). 

Figure 10. Indicated are the HOMO and LUMO orbital energies obtained form EHT calculations for a variety of reactants. In the center are estimated orbital energies for a canonical metal cluster.

Groups which add conjugation such as olefinic, acetylenic and aromatic groups lower the LUMO orbital energy one third to one half as much as the HOMO energy. 

Taking the results from the absorption and electrochemical studies into account (see above), it was necessary to evaluate the relationship between the energy levels of the pristine building blocks. For this reason, we have optimized (DFT) the structures of the reference compounds, i.e. 13a-c and 14a-c, and their pristine building blocks methylfulleropyrolidine 1, ZnP, H2P, and oPPEs in order to investigate their HOMO/LUMO orbital energies. Thereby, important evidence for the interactions between the donor, bridge and acceptor sites was found. 

Fig. 9.20 HOMO/LUMO orbital energies as resulted from DFT optimizations of the building blocks of the triads in relation to the triads themselves. The HOMO energies are represented in red and LUMO energies in green...

Figure 9.49 represents the HOMO/LUMO orbital-energy distribution in 18a,b and the hypothetical trimer with three oligofluorene units as linker. Again, we clearly distinguish the HOMO and LUMO orbitals localized on the donor and acceptor, respectively, demonstrating the charge-transfer features in these triads. 

Yokoyama and coworkers investigated the discolouration of titanylphthalocyanine 60, and related porphyrins by silyl radicals derived from methylphenylpolysilane by molecular orbital methods60. Calculated values of AN, the index derived from the hard and soft acids and bases concept was determined from HF/3-21G calculated ionization potentials, electron affinities, and HOMO and LUMO orbital energies of the systems of interest. These studies predict that PhMe2Si should donate an electron readily to 60 to form 60 (equation 18). This prediction is of direct relevance to observations that irradiation of titanylphthalocyanine-coated methylphenylpolysilane films leads to discolouration of the film60. 

Some the results of calculations (total energy, heat of formation, HOMO and LUMO orbitals energies and so on) are collected in Table 2. 

Table 5.1 gives for four simple molecules the values of HOMO/LUMO orbital energies calculated with accurate augccpVTZ-GTO3 basis sets at the University of Modena and the values of the intermolecular l/3ls resulting from Equation (5.2). 

Table 5.1 Best values of HOMO/LUMO orbital energies from accurate augccpVTZ-MO calculations3 and estimated intermolecular interaction integral...

HOMO and LUMO orbital energies lumo homo 20, 77... 

Table 6-2. HOMO and LUMO orbital energies (T2, T3) of diazomethane and its hetero-analogous compounds (after Caramella et al., 1977a Houk and Yamaguchi, 1984), in kJ mol ...

Figure 9. Gap between HOMO and LUMO orbital energy for various conjugated systems oligoynes, oligoenes, and fullerenes. The upper scale is for the oligoynes and oligoenes and the lower scale for fullerenes.

Until now there are no data on electron affinities of allenes (or other cumulenes) in the literature. From Equation 95 one would estimate a value of y4 (3c) = — 1.87 eV for the 3c orbital in allene (11). This is more negative than the value found for ethylene A = —1.55 eV (147)) by —0.32 eV. CNDO/S calculations give a difference of —0.19 eV for the LUMO orbital energies of allene (11) and ethylene. 

We often assume the double oeeupaney of orbitals within what is called the closed shell. The latter term has an approximate eharacter (Figs. 8.4 and 8.5). It means that for the studied system, there is a large energy difference between HOMO and LUMO orbital energies. 

LUMO orbital energies of the lowest unoccupied orbitals... 

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