Orbit diagram

Refer to the molecular orbital diagrams of allyl cation (Figure 10 13) and those presented earlier in this chapter for ethylene and 1 3 butadiene (Figures 10 9 and 10 10) to decide which of the following cycloaddition reactions are allowed and which are forbidden according to the Woodward-Floffmann rules... 

These full color transparencies of illustrations from the text include reproductions of spectra orbital diagrams key tables computer generated molecular models and step by step reaction mechanisms... 

Figure 7.31 Walsh molecular orbital diagram for AH2 molecules...

Fig. 2. Simplified molecular orbital diagram for a low spia octahedral complex, such as [Co(NH3 )g, where A = energy difference a, e, and t may be antisymmetric (subscript ungerade) or centrosymmetric (subscript, gerade) symmetry orbitals. See text.

For conjugated carbonyl compounds, such as a,) -enones, the orbital diagram would be similar, except for the recognition that the HOMO of the ground state is ij/2 of the enone system, rather than the oxygen lone-pair orbital. The excited states can sometimes be usefully represented as dipolar or diradical intermediates ... 

Fig. 15.1 Molecular orbital diagram of inUamolecular donor (D) - chalcogen (E) interactions...

Figure 19.14 Molecular orbital diagram for an octahedral complex of a first series transition metal (only a interactions are considered in this simplified diagram).

Figure 19.17 Schematic molecular energy level diagram for CO. The Is orbitals have been omitted as they contribute nothing to the bonding. A more sophisticated treatment would allow some mixing of the 2s and 2p, orbitals in the bonding direction (z) as implied by the orbital diagram in Fig. 19.18.

Figure B A qualitative molecular orbital diagram for ferrocene. The subscripts g and u refer to the parity of the orbitals g (German gerade, even) indicates that the orbital (or orbital combination) is symmetric with respect to inversion, whereas the subscript u (ungerade, odd) indicates that it is antisymmetric with respect to inversion. Only orbitals with the same parity can combine.

The electron configuration or orbital diagram of an atom of an element can be deduced from its position in the periodic table. Beyond that, position in the table can be used to predict (Section 6.8) the relative sizes of atoms and ions (atomic radius, ionic radius) and the relative tendencies of atoms to give up or acquire electrons (ionization energy, electronegativity). 

For many purposes, electron configurations are sufficient to describe the arrangements of electrons in atoms. Sometimes, however, it is useful to go a step further and show how electrons are distributed among orbitals. In such cases, orbital diagrams are used. Each orbital is represented by parentheses (), and electrons are shown by arrows written f or, depending on spin. 

To show how orbital diagrams are obtained from electron configurations, consider the boron atom (Z = 5). Its electron configuration is ls22s22p1. The pair of electrons in the Is orbital must have opposed spins (+j, or f j). The same is true of the two electrons in the 2s orbital. There are three orbitals in the 2p sublevel. The single 2p electron in boron could be in any one of these orbitals. Its spin could be either up or down. The orbital diagram is ordinarily written... 

With the next element, carbon, a complication arises. In which orbital should the sixth electron go It could go in the same orbital as the other 2p electron, in which case it would have to have the opposite spin, [. It could go into one of the other two orbitals, either with a parallel spin, f, or an opposed spin, Experiment shows that there is an energy difference among these arrangements. The most stable is the one in which the two electrons are in different orbitals with parallel spins. The orbital diagram of the carbon atom is... 

Orbital diagrams for atoms with five to ten electrons. Orbitals of equal energy are all occupied by unpaired electrons before pairing begins. 

Following this principle, the orbital diagrams for the elements boron through neon are shown in Figure 6.10. Notice that—... 

Construct orbital diagrams for atoms of sulfur and iron. 

Strategy Start with the electron configuration, obtained as in Section 6.5. Then write the orbital diagram, recalling the number of orbitals per sublevel, putting two electrons of opposed spin in each orbital within a completed sublevel, and applying Hund s rule where sublevels are partially filled. 

SOLUTION Recall from Example 6.6 that the electron configuration of sulfur is ls22s22p63s23p4. Its orbital diagram is... 

Reality Check To construct an orbital diagram, start with the electron configuration and apply Hund s rule. 

Give the symbdofthe atom with the following orbital diagram beyond argon. 

According to this model, a covalent bond consists of a pair of electrons of opposed spin within an orbital. For example, a hydrogen atom forms a covalent bond by accepting an electron from another atom to complete its Is orbital. Using orbital diagrams, we could write... 

Strategy First (1) find the total number of electrons (Z Co = 27). Then (2) find the electron configuration the first 18 electrons form the argon core, and the remaining electrons enter the 3d sublevel. Finally (3) apply Hund s rule to obtain the orbital diagram. 

Give the electron configuration and/or orbital diagram of a transition metal cation. 

Derive orbital diagrams for high-spin and low-spin complexes. 

Write an abbreviated orbital diagram and determine the number of unpaired electrons in each species in Question 25. 

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