Geometry hybridization scheme from

In valence bond theory, the particular hybridization scheme to follow (sp versus p for example) for a given molecule Is determined computationally, which Is beyond our scope. In this book, we will determine the particular hybridization scheme from the VSEPR geometry of the molecule, as shown later In this section. 

TABLE 10.3 Hybridization Scheme from Electron Geometry... 

Benzene has a total of 30 valence electrons. To describe the bonding in benzene using hybrid orbitals, we first choose a hybridization scheme consistent with the geometry of the molecule. Because each carbon is surrounded by three atoms at 120° angles, the appropriate hybrid set is sp. Six locahzed C—C tr bonds and six localized C—H <7 bonds are formed from the sf hybrid orbitals, as shown in Figure 9.26(a). Thus, 24 of the valence electrons are used to form the a bonds in the molecule. 

The hybridization traditionally assumed for the trigonal bipyramid is sp d, the configuration in the initial geometry being that of the constituent AOs 3s a y,3pz a"y, (3px, 3py)(e ), 3d2 .2 a-2 y2(a ) ). It can be seen on the left side of Fig. 11.1 that the configuration based on the five combinations of halide-ion closed shells is identical. From the point of view of configurational symmetry, inclusion of a d orbital in the hybridization scheme in order to produce five equivalent covalent bonds is harmless but unnecessary. 

Number of Electron Groups Electron Geometry (from VSEPR Theory) Hybridization Scheme... 

FIGURE 24.11 Common Hybridization Schemes in Compiex ions The valence bond model hybridization schemes can be deduced from the geometry of the complex ion. 

The molecule ethylene, C2H4, consists of an array of two carbon and four hydrogen atoms, in which each carbon is bonded to the other carbon and two hydrogens. Unlike methane, there are only three other atoms attached to carbon and therefore the geometry around each carbon is different than in methane. The VESPR rule requires that the three attached atoms be arranged in the same plane as the carbon and spaced approximately 120° apart from one another to minimize repulsions between the bonding electrons. This cannot be achieved using sp hybrid orbitals and so a different hybridization scheme is required, one that will result in three... 

Regarding the structure and function of nitrogenases in producing ammonia from N2, Sellmann has studied several model systems wherein heterolytic activation of H2 occurs on sulfur ligands (87). A core geometry based on a hybrid of the FeMoco active site structure with a dinuclear diazene complex, [Fe( NHS4 )]2(p-N2H2), is a proposed model (Scheme 4). 

For the Group 14 metallocenes, a simplified rationalization for the bent geometries uses valence bond hybridization arguments.143 The metal atom is considered approximately sp2 hybridized, with the lone pair of valence electrons occupying a stereochemically distinct region around the metal center (Fig. 12). Support for this scheme came from low-level MO calcula-... 

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