Molecular orbitals associated with the

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... 

One of the most remarkable features of the all-silicon backbone is that it leads to the delocalisation of a-electrons, a phenomenon which is essentially unknown in carbon chemistry.This can be understood in terms of the nature of the molecular orbitals associated with the Si-Si a-bonds. These are more diffuse than those associated with C-C a-bonds as they are constructed from higher energy 3s and 3p atomic orbitals. This leads to significant... 

As we have seen previously (Chapter 5), the eigenfunction for a polyelec-tronic atom is antisymmetric with respect to the exchange of the coordinates of any two electrons, and can be expressed as a Slater determinant whose elements are the various occupied spin-orbitals (or a linear combination of Slater determinants, in the case of open-shell atoms). The same appfies to polyelectronic molecules, the atomic orbitals being replaced by the various occupied molecular orbitals associated with the a and /3 spin-functions spin molecular orbitals. Thus, for the molecules H2O, NH3 or CH4 having five doubly occupied m.o.s (one core s orbital and four valence m.o.s), we have... 

The polycyclic anions were first prepared by metal reduction in 1914 by Schlenk et al.5 a) and studied later by Schlenk and Bergmann 5 b). This class of conjugated anions opened a new era in carbanion chemistry by pointing out the electron transfer process as a source for charged species. The mechanism of the metal reduction of polycyclic hydrocarbons has been investigated and is well established 1,215 18-68>. The addition of two electrons to the fully conjugated (4n + 2)n-molecules yields 4mt paratropic systems 2°. 137 139>. The chemistry of this reaction is simple, with electrons initially on the alkali metal going to 7t-molecular orbitals associated with the aromatic hydrocarbon molecule (Eq. 13). 

The extrinsic dimerization has two effects. First, it causes an increased intrinsic dimerization, as shown in Fig 4.10. Second, it lifts the degeneracy of the A and B phases, as shown in the plot of the ground state energy in Fig. 4.1. This causes a linear confinement of the soliton-antisoliton pair, because the energy to create a B phase relative to the A phase increases linearly with the soliton-antisoliton separation. This new property of soliton-antisoliton confinenment is illustrated by the localized Wannier orbitals associated with the soliton, and antisoliton, These are obtained from the molecular orbitals associated with the mid-gap electronic states, V n > (described in Section 4.5) by inverting eqn (4.33). Thus,... 

The molecular orbitals associated with the TT electrons of an allylic system. 

Therefore, when the nucleophile approaches the alkyl halide to form a new bond, the nonbonding molecular orbital of the nucleophile (its HOMO) must interact with the empty antibonding molecular orbital associated with the C—Br bond (its LUMO). 

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