Orbital hybridization ethane

The same kind of orbital hybridization that accounts for the methane structure also accounts for the bonding together of carbon atoms into chains and rings to make possible many millions of organic compounds. Ethane, C2H6, is the simplest molecule containing a carbon-carbon bond. 

The first three alkanes are methane (CH4), ethane (CH3CH3), and propane (CH3CH2CH3). All can be described according to the orbital hybridization model of bonding based on sp hybridization of carbon. 

The orbital hybridization model of covalent bonding is readily extended to carbon-carbon bonds. As Fignre 1.23 illustrates, ethane is described in terms of a carbon-carbon O bond joining two CH3 (methyl) groups. Each methyl group consists of an -hybridized carbon attached to three hydrogens by o bonds. Overlap of the... 

Consequently, groups joined by single bonds rotate relatively freely with respect to one another. (We discuss this point further in Section 4.8.) In Fig. 1.20 we show a calculated structure for ethane in which the tetrahedral geometry derived from orbital hybridization is clearly apparent. 

We can account for the structure of ethyne on the basis of orbital hybridization as we did for ethane and ethene. In our model for ethane (Section 1.12B) we saw that the carbon orbitals are sp hybridized, and in our model for ethene (Section 1.13) we saw that they are sp hybridized. In our model for ethyne we shall see that the carbon atoms are sp hybridized. 

FIGURE 2 10 The C—C ct bond in ethane pictured as an overlap of a half filled sp orbital of one carbon with a half filled sp hybrid orbital of the other... 

Here, the bonding between carbon atoms is briefly reviewed fuller accounts can be found in many standard chemistry textbooks, e.g., [1]. The carbon atom [ground state electronic configuration (ls )(2s 2px2py)] can form sp sp and sp hybrid bonds as a result of promotion and hybridisation. There are four equivalent 2sp hybrid orbitals that are tetrahedrally oriented about the carbon atom and can form four equivalent tetrahedral a bonds by overlap with orbitals of other atoms. An example is the molecule ethane, CjH, where a Csp -Csp (or C-C) a bond is formed between two C atoms by overlap of sp orbitals, and three Csp -Hls a bonds are formed on each C atom. Fig. 1, Al. 

Section 2.7 The carbon-carbon bond in ethane is a a bond in which an sp hybrid orbital one carbon overlaps with an sp hybrid orbital of the other. 

Although it is rather certain that electrostatic interactions of polar groups, steric hindrance, and partial double bond character due to conjugation will all be of importance in selected molecules, the explanation of the barrier in ethane probably requires something else. Though far from being proven and certainly not now useful for prediction, the idea that the ethane barrier arises from repulsion of C—H bond orbitals on the carbons, due to their being more concentrated than sp hybrids, seems the most plausible picture available. 

Figure 1.17 The hypothetical formation of the bonding molecular orbitals of ethane from two sp -hybridized carbon atoms and six hydrogen atoms. All of the bonds are sigma bonds. (Antibonding sigma molecular orbitals — are called a orbitals — are formed in each instance as well, but for simplicity these are not shown.)... 

We have already explained. In terms of hybridisation, how a carbon atom can form four sp hybrid orbitals (see p. 47). We can apply this concept to explain the bonding in alkanes. Ethane is taken as an example of a typical alkane. The four sp hybrid orbitals on each carbon atom will overlap end-on with four other orbitals three hydrogen Is orbitals and one sp hybrid orbital on the other carbon atom. Four cr bonds will be formed and they will adopt a tetrahedral arrangement. This is illustrated for ethane in the diagram. 

Because they have no ionic states, the previous covalent-only results have too high a kinetic energy contribution, as discussed in Chapter 2. Adding all possible ionic states would lead to the very large number of basis functions quoted in the first paragraph of the discussion of ethane. We will consider the following physical arguments that may be used to limit the number of ionic state functions. This will all be done in the context of hybrid orbitals on the C atoms. 

Table 3.13. Energies for various hybrid orbital calculations of D d < nd D h ethane.

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