Benzene orbitals

The only example of P.E. spectra of a mixed arene-carbonyl metal complex is that of Cr(bz)(CO)3 reported by Guest et al. (76). In the latter compound, the two d-bands observed in the spectrum of Cr(bz)2 merge into a single band, with maximum at 7.42 eV, containing the ionizations of all six -electrons. A second band, at 10.70 eV, is related to a benzene orbital, while a third band, at 12.70 eV, has both carbonyl and benzene character. The assignment is supported by theoretical calculations and by comparison between He(I) and He(II) spectra (76). 

Figure 10b, c, and d. Since these all have zero overlap with the antisymmetric benzene orbital shown in Figure lOe, the overlap determinant vanishes and the interconversion is thermally forbidden. Trindle24 has given a number of other examples, using his more elaborate procedure, and the method appears to work well. 

Ag+ has a low-lying LUMO, so it interacts strongly with one of the relatively high-energy benzene HOMOs. o (I2) lies at much higher energy, so it overlaps better with the VP1 benzene orbital. 

The 7r energy levels, along with the molecular orbital wavefunctions, are pic-torially displayed in Fig. 7.1.12. Since there are six n electrons in benzene, orbitals a2u and e % are filled, giving rise to a 1 /V ig ground state with the total n energy... 

Fig. 3. One of the six equivalent carbon-centred benzene orbitals obtained from BOVB calculations.

T, iTj benzene orbitals can also be removed by replacement of a C-atom in the benzene skeleton by a heteroatom such as N. Energies of NISs of N-heterocyclics were obtained by electron scattering methods, and an example is shown in Table 5. 

The HOMO and LUMO orbitals of a monosubstituted benzene where the substituent, X (= NH2, OH or F), is a neutral rr-donor, may be obtained through interaction of the benzene HOMO and LUMO orbitals with the substituent lone pair according to the principles discussed in Section III.B. Being an occupied orbital, the lone pair orbital will be closer in energy to the occupied benzene orbitals than the unoccupied ones (Fig. 8). As a result, it will interact mainly with the occupied orbital of appropriate symmetry, to give two new orbitals. The antibonding o)mbination of this interaction now becomes the HOMO and may be seen to conform to the quantitative data in Fig. 6. The LUMOs for aniline, phenol, and fluorobenzene are the essentially unaffected benzene LUMO, in agreement with the quantitative data (Fig. 7). 

Finally, analysis of the interaction of a high-lying vacant orbital with the benzene orbitals is shown in Fig. 10. Here we see that the predominant inter-... 

The second factor is the following either the lone pair on the N(l) or the 0 - N(l) bonding electrons are able to interact with both the 67t-benzene orbital and the n orbital of the C(2) - C(3) if the O - N(1) bond deviates from the plane of the indole (N, Fig. 4). In addition, the resulting sp -like lone pair orbital of the N(l) can form a hydrogen bond with the 1-hydroxy hydrogen. 

Molecular orbital (MO) diagram of [Cr(CeHg)2] (top) and interactions of the benzene orbital with the Cr orbitals of appropriate symmetry to form [Cr(CeH6)2] (bottom)... 

Figure 7. Molecular orbitals for phthalan and the electronic transition producing the Sj(K, 71 ) state. The correlation to benzene orbitals is shown.

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