Hybrid orbitals other types

Bond distances for some important bond types are given in Table 1.5. As can be seen in this table, carbon bonds are shortened by increasing s character. This is most often explained by the fact that, as the percentage of s character in a hybrid orbital increases, the orbital becomes more like an s orbital, and hence is held more tightly by the nucleus than an orbital with less s character. However, other explanations have also been offered (see p. 37), and the matter is not completely settled. 

Now that we know how to determine hybridization states, we need to know the geometry of each of the three hybridization states. One simple theory explains it all. This theory is called the valence shell electron pair repulsion theory (VSEPR). Stated simply, all orbitals containing electrons in the outermost shell (the valence shell) want to get as far apart from each other as possible. This one simple idea is all you need to predict the geometry around an atom. First, let s apply the theory to the three types of hybridized orbitals. 

The orbitals containing the bonding electrons are hybrids formed by the addition of the wave functions of the s-, p-, d-, and f- types (the additions are subject to the normalization and orthogonalization conditions). Formation of the hybrid orbitals occurs in selected symmetric directions and causes the hybrids to extend like arms on the otherwise spherical atoms. These arms overlap with similar arms on other atoms. The greater the overlap, the stronger the bonds (Pauling, 1963). 

In this chapter, procedures for drawing molecular structures have been illustrated, and a brief overview of structural inorganic chemistry has been presented. The structures shown include a variety of types, but many others could have been included. The objective is to provide an introduction and review to the topics of VSEPR, hybrid orbitals, formal charge, and resonance. The principles discussed and types of structures shown will be seen later to apply to the structures of many other species. 

In addition to the two types of hybrid orbitals (sp and sp2) discussed so far, there are a number of others, representing different mixtures of atomic orbitals, that are commonly used in the description of directed covalent bonding. For example, one s and three p orbitals will lead to a set of four sp3 hybrid orbitals two dorbitals, one s orbital, and three p orbitals give a set of six d2spz orbitals. The general rule here is as follows ... 

The simplest compound of this type is iminophosphorane, H3P=NH, whose derivatives are very numerous, including R3P=NR, ChP=NR, (RO)3P=NR, and Ph3P=NR. In these compounds the P atom uses its sp3 hybrid orbitals to form four a bonds, and is also strengthened by djr-pjr overlap with N and other atoms. 

The diagram indicates that there are still separate s and p orbitals. Experimental evidence indicates that the bonds formed between carbon and other atoms (for example, four hydrogen atoms) are all the same. That is, they all behave as though they are the same type of orbital. The accepted explanation for this is that the four orbitals form a new type of orbital known as a hybrid. In this case, because the new orbitals involve one s orbital and three p orbitals, the new orbitals are known as sp3 (pronounced s-p-three —don t mistake it for an exponent) hybridized orbitals, shown in Figure 7.1 ... 

The moments in Table 2 also do not depend on what types of d functions are used to construct the hybrids. In other words, the moments do not depend on the m quantum number. For example, a hybrid which uses only dz2 orbitals, will have the same moments as a hybrid which uses only dxi yi orbitals. This is, perhaps, an obvious point as the moments we are discussing are radial moments angular characteristics in the hybrid density are spherically averaged during the integration over the solid angle. 

If all orbital interactions of the type described by Eq. (8.27) are included in the calculations, any result obtained is independent of the combination of a.o.s used, if any, i.e. four pure atomic orbitals, four sp hybrid orbitals, three sp and one p orbital, two sp and two p orbitals, etc. In particular, at a given level of approximation, the linear combinations of hybrid (and other)... 

The small interaction between the two C hybrid orbitals, as well as the other orbital interactions, can be related to the corresponding overlap integrals and these depend on the geometry of the HC CH fragment. In particular, the dihedral angle 0 between the H(1)CC and CCH(2) planes is an important factor. As a consequence, vicinal coupling constants are of extreme value in conformational studies. The relationship (the Karplus equation) is of the following type ... 

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