Ji molecular orbitals

The Patemo-Biichi reaction is a photocycloaddition reaction of a n,ji carbonyl compound to an alkene in the ground state from either the Si or the rl i state. The reaction can occur through the initial C O bond formation or through a previous formation of the C—C bond. A frontier orbitals approach can be used to explain the formation of oxetanes. We can observe the HSOMO-LUMO interaction in which the half-occupied ji carbonyl orbital interacts with the unoccupied ji molecular orbital of an electron-deficient alkene, and a C,0-biradical is formed. The LSOMO-HOMO interaction in which the half-occupied n orbital of the carbonyl O atom interacts with the ji orbital of an electron-rich alkene, and a C,C-biradical is formed [13, 14]. 

In addition to the a bonds, four localized ji molecular orbitals result from the combination of two occupied metal d orbitals and the diazene n orbitals. Three... 

If the substituent is bonded to an sp carbon atom not involved in the Ji molecular orbitals formation, its electrical effect is only local, assuming that a electron delocalization is negligible. Substituents bonded to sp or sp carbon atoms can exert both localized and delocalized effects. 

FIGURE 10.6 Calculated main n, ji, ji molecular orbitals of two difunctional photoinitiators - dfll (left) and dfI2 (right) - at a B3LYP/6-31G level. See text. 

It can be seen from Figure 8.17 that the 2p and 2p orbitals produce zero net overlap with the hydrogen 1 s orbital because the overlap of the positive lobe cancels out the overlap of the negative lobe. Therefore, the hydrogen Is orbital makes no contribution to the Ji molecular orbitals. 

This is a quadratic equation in x with the following roots x = 2.62 and 0.382. The allowed values of x are 1.62 and 0.62, which lead to the following energies for the four ji molecular orbitals ... 

Ji-molecular orbitals. co°s and (0°a, thus represent suprafacial and antarafacial addition to vacant single orbital. Suprafacial and antarafacial addition to doubly filled atomic orbitals are represented by the symbols (O s and ca a, respectively. Generalized rules for electrocyclic reactions, cycloadditions and sigmatropic reactions are depicted below ... 

In Fig. 6-7, similar procedures are followed for the metal d orbitals. The 42 2orbital-symmetry matches with the in-plane group combination ((Ji-02+molecular orbitals described in Eq. (6-13). 

Figure 2.13 n and k molecular orbitals associated with the >C=C< chromophore. Both the n- and Ji -orbitals lie in the plane of the paper... 

Hitherto, thio ether formation has clearly been proved only in the case of the ji-donor substituted 4-nitrosophenetol and the electron-rich l-methyl-2-nitrosoimidazole. The low yields of this adduct (about 2% at 1 1- and about 10% at 1 5-stoichiometry for 4-nitrosophenetol reacting with GSH56) may be the reason for its rare discovery. However, other nitrosoarenes should yield this family, too. Semiempirical molecular orbital calculations (MNDO) indicate a similar positive charge at the exposition of the N-(methylthiol-S -yl)-aniline cation and -4-anisole cation as well (Scheme 6). Furthermore, formation of l-(glutathion-S -yl)-2-naphthylamine was reported to occur in mixtures of 2-nitrosonaphthalene and GSH12. 

In its two anti- n orbital (Ji ), there are two single electrons. The orbital can either accept or donate one electron, which can be either HOMO or LUMO. From Fig. 1.8, the energy values and symmetry of the frontier molecular orbital of galena, pyrite, HS , EX , and oxygen are shown in Table 1.5. 

Our next exan le, the TMM diradical, is a more challenging case because its frontier orbitals are exactly degenerate. The 7C-system of TMM is shown in Figure 6 four ic-electrons are distributed over four molecular ji-type orbitals. Due to the exact degeneracy between the two e orbitals at the Ds structure, Hund s rule predicts the ground state of the molecule to be a triplet 2 state (similar to the T-state in ethylene). This is confirmed by both the experimental and theoretical findings (38-43). 

As far as the orbital overlap method is concerned (6), the energies of the anti-bonding molecular orbitals are expressed ) (considering only a and ji bonding) as a function of the energy parameters eg and ew. 

Figure 1.10 The shape of selected molecular orbitals for the diatomic molecule AB, where B is more electronegative than A (a) a, (b) a, (c) it and (d) ji. ...

None of the theories proposed before 1951 to explain the nature of the bonding in metal-olefin complexes was entirely satisfactory (35). Chatt (S3) suggested that, in addition to the ordinary coordinate bond, some sort of bond involving the filled d-orbitals of the metal atom was essential for coordination of the olefin, but such a bond was difficult to formulate until Dewar (64) described it in terms of molecular orbitals. The structure which he proposed for the silver-olefin complexes, and that subsequently proposed for the platinum-olefin complexes by Chatt and Duncanson (35) are shown schematically in structures (I) and (II). The type bond, which has also been called a ji-bond (64, 4), is formed by the overlap of the filled bonding... 

In this chapter, simple Hiickel molecular orbital (SHMO) theory is developed. The reference energy, a, and the energy scale in units of ji are introduced. 

If the bond formed between two adjacent atoms is symmetric along the axis between the two nuclei, we refer to the bond as a o-bond. In contrast, the bond that is formed between two electrons in the p-orbitals is called a ji-bond. These molecular orbitals have a very different shape. The single bond between two carbon atoms (-C-C-) is formed between electrons in the sp3-orbitals (o-bond) of two adjacent carbon atoms (Figure la). A double bond between two C-atoms (-C=C-) consists of a o-bond formed between electrons in the sp2 orbitals of two adjacent C-atoms, and a 7i-bond formed between two 2p-orbitals (Figure 2-1). 

The calculated molecular orbital (MO) energies are compared to those available from photoelectron spectra. The first four MOs of thiepine 1 are calculated to lie at 8.19, 10.08, 10.32, and 11.64 eV (7t 4, ji 3, n"2, and ng, respectively). The basic distribution of these orbitals is in good agreement with the photoelectron spectra of several substituted thiepines. For example, a linear relationship (slope = 1.36, intercept —2.33, R2 = 0.988) can be obtained by plotting the experimental ionization energies for 2,7-di- vt-butylthiepine 11 versus the calculated orbital energies for thiepine 1 <85JA6874>. 

Flere, as in metal model wave number k — 2%jjNax (j — 0, +1,..., .N/2), Pi, and p2 are exchange integrals for short and long bonds in the lattice dimer unit, respectively, and it was obvious that Pi > p2. As is shown in Figure 10.2 ji orbital levels form two bands divided by the band gap AE. The minimal value of gap AE (Afs0) between highest occupied molecular orbitals... 

---