And sp3 hybridization

The mechanism described in Scheme 2 was rejected on the grounds that the steric requirement for the abstraction of a hydrogen atom from -CHD-of species (IV) could not be met. Assuming an atomically flat surface, and sp3 hybridization of the carbon atom bonded to the surface, the plane of the Ce-ring in (IV) is in such a configuration that the hydrogen atom of -CHD- is directed away from the surface, and the deuterium atom toward the surface. Thus, unless the species is adsorbed near a step in the metal lattice, the loss of this hydrogen and the formation of a second carbon-metal bond would require a very considerable distortion of adsorbed species. 

Additional bonds are thus donor bonds, and to accept electron pairs from neutral and anionic ligands, zinc uses the two remaining 4p orbitals to form sp2 and sp3 hybrids. In the absence of steric effects, discrete, homoleptic, anionic tri- and tetraorganozinc compounds (zincates) have almost always ideal trigonal-planar and tetrahedral geometries, respectively. 

Representative organic syntheses. A solution of the naked fluoride ion may be generated by dissociation of KF in an acetonitrile or benzene solution containing 18-crown-6 (Liotta Harris, 1974). The considerable nucleophilicity of this anion under these conditions is demonstrated by the fact that it is capable of displacing leaving groups from both sp2 and sp3 hybridized carbons in a number of structural environments. 

The methyl carbanion, CH3, has bond angles close to that in a tetrahedral arrangement of atoms, 109°, indicating 4 electron groups around the central C atom and sp3 hybridization. The lone pair of electrons exerts significant repulsive force on the electrons in bonding orbitals and must be counted as an electron group. 

It can be imagined that the bonds can be broken at any location, that is, with an oxygen, hydroxy, silicon, or aluminum exposed. In this case, it could further be imagined that s-, p-, and sp3-hybridized orbitals would be on the surface. This... 

Hybridization occurs between two or more different types of orbitals (generally s, p or d orbitals). For example, there are three types of hybrid orbitals which may occur between the s and p orbitals, these are named as sp, sp2 and sp3 hybrid orbitals. 

Fig. 15.1 Classification of sp2- and sp3-hybridized nanostructured carbon materials. CNTs are considered as open-end tubes, thus also exposing prismatic edge surfaces.

In hybridizations involving nonequivalent hybrid orbitals, such as sp tl, it is usually possible to resolve the set of hybrid orbitals into subsets of orbitals that are equivalent within the subset, as the sp2 subset and the dp subset. We have seen (Chapter 5) that the nonequivalent hybrids may contain fractional s and p character, e.g., the water molecule which uses bonding orbitals midway between pure p and sp3 hybrids. For molecules such as this, we can divide the four orbitals into the bonding subset (the bond angle is 1041°) and the nonbonding subset (angle unknown). We can then apply Eq. 6.1 to each subset of equivalent orbitals. In water, for example, the bond angle is 1041°, so... 

Shape is crucial, both 7.2 Strengths of Covalent Bonds 7.11 Hybridization and sp3 Hybrid... 

The C—Cl bond in chloroethylene [173.0(4) pm] is by about 4-5 pm shorter than the C—Cl bond in chloromethane. This difference is larger than that between the covalent radii of sp2 and sp3-hybridized carbon (74 and 77 pm, respectively). The C—Cl bond distances... 

The carbon of methanol has four bonding pairs of electrons, so it is tetrahedral and sp3 hybridized. The geometry of the four electron pairs of oxygen is also tetrahedral, so it is sp3 hybridized too. 

For the interaction potential between hydrogen and carbon, we introduce a new procedure to derive the Lennard-Jones parameters from existing parameters that are appropriate for carbon atoms with sp2 and sp3 hybridizations. These parameters may come from existing force fields, and may have been obtained using either experimental or ab initio results. The L-J parameters a and s are made explicitly dependent on the radius of the nanotube, r, using the following equations ... 

The theory proposed by Dewar et al. (154) is also based on a tr-bonded P—N skeleton of sp2-hybridized nitrogen and sp3-hybridized phosphorus but postulates a pair of linear combinations of phosphorus dxz and dy orbitals for overlap with an adjacent nitrogen p2 orbital. The result is a system of almost independent three-center 7t-bonds containing two phosphorus atoms and one nitrogen atom (Fig. 18). More detailed calculations appear to support this theoretical treatment (167,168,171, 172, 318) and indicate that conjugation beyond the three-center islands is of minor importance in cyclotriphosphazene derivatives (167). X-Ray crystallographic data for heterogeneously substituted cyclophosphazene derivatives (Section V,C) and evidence... 

Murray-Rust P, Glusker JP (1984) Directional hydrogen-bonding to sp2 and sp3 hybridized oxygen atoms and its relevance to ligand-macromolecular interactions. J Am Chem Soc 106 1018-1025... 

Figure 4. The sp, sp2, and sp3 hybrid density functions in the 12-plane of position space. As is often the case, orbitals that are quite different from one another in momentum space, can appear very similar in the corresponding position space representation.

Although it will not be important for our purposes, the dsp3 hybrid orbital set is different from the hybrids we have considered so far in that the hybrid orbitals pointing to the vertices of the triangle (often called the three equatorial hybrid orbitals) are slightly different in shape than the other two (the axial orbitals). This situation stands in contrast to the sp, sp1, and sp3 hybrid sets in which each orbital in a particular set is identical in shape to the others. 

The simplest member of the saturated hydrocarbons, which are also called the alkanes, is methane (CH4). As discussed in Section 14.1, methane has a tetrahedral structure and can be described in terms of a carbon atom using an sp-J hybrid set of orbitals to bond to the four hydrogen atoms (see Fig. 22.1). The next alkane, the one containing two carbon atoms, is ethane (C2H6), as shown in Fig. 22.2. Each carbon in ethane is surrounded by four atoms and thus adopts a tetrahedral arrangement and sp3 hybridization, as predicted by the localized electron model. 

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