Highest-occupied molecular orbital benzene

In addition to electrophilic attack on the pyrrole ring in indole, there is the possibility for additions to the fused benzene ring. First examine the highest-occupied molecular orbital (HOMO) of indole. Which atoms contribute the most What should be the favored position for electrophilic attack Next, compare the energies of the various protonated forms of indole (C protonated only). These serve as models for adducts formed upon electrophilic addition. Which carbon on the pyrrole ring (C2 or C3) is favored for protonation Is this the same as the preference in pyrrole itself (see Chapter 15, Problem 2)1 If not, try to explain why not. Which of the carbons on the benzene ring is most susceptible to protonation Rationalize your result based on what you know about the reactivity of substituted benzenes toward electrophiles. Are any of the benzene carbons as reactive as the most reactive pyrrole carbon Explain. 

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 2-2. Spatial representation (ball-and-stick model) of benzene, with C-atoms in grey and H-atoms in white. The dotted lines between the C-atoms represent the delocalized electrons. The image on the right shows the surface area of the highest occupied molecular orbital (HOMO). Note how the 71-electrons are above and below the benzene ring.

The molecular orbitals of benzene are schematically represented in Fig. 3. The first excited state of benzene cannot be described by one electron configuration, due to the degeneracy of the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs). The Si state of benzene (B2u) can be represented as 4>24>4 - 4>35 and the S2 or state (Biu) as 4>24>5 - 4)3(t,4-... 

In phenyl-substituted polysilanes, the problems become more complicated because the benzene n electron system is mixed with the a (Si-Si) orbitals and the highest occupied molecular orbital is assigned to a linear combination of 7r (C6H5) and a (Si—Si) orbitals452. Similar properties are found in mixed-substituted methyl-phenylpolysilanes, where the effect of extension of the 3 d molecular orbitals of the polysilane-chain is found to be minimal453. ... 

The highest energy orbital that contains electrons is called the highest occupied molecular orbital (HOMO). For benzene, the degenerate orbitals V2 j/3 are the HOMOs. 

Fig. 3 Schematic diagram of the canonical MOs of benzene, phenide anion and phenylacetylene. The highest occupied molecular orbital (HOMO) and three lower ones HOMO-1, HOMO-2 and HOMO-3 are shown along with their symmetry representations...

The UV spectrum of benzene is interpreted as the excitation of an electron from the highest occupied molecular orbital (HOIMO, bonding n MO) to the lowest unoccupied molecular orbital (LUIMO, antibonding n MO ). The bond order of the TT-system changes from 3 to 2. 

Fig. 2.4. Four views of benzene, (a) a chemical model of the molecule (b) an isocharge surface (c) the HOMO, or highest occupied molecular orbital (d) the LUMO, or lowest unoccupied molecular orbital.

Some donor-acceptor complexes show two distinct maxima in the charge-transfer band. Examples are the complexes of certain substituted benzenes and tetracyanoethylene (TCNE) . The most likely explanation of the multiple maxima is as follows In molecules of high symmetry such as benzene the highest occupied molecular orbitals are degenerate (Fig. 10). On sub-... 

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