Ethane hybrid orbitals

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. 

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.

As can be seen from Table 2, the amount of s-character of the CH hybrid orbital of 1 is indeed increased relative to that of the CH hybrid orbitals of ethene, ethane and methane while at the same time the s-character of the CC hybrid orbitals is decreased. This seems to confirm predictions based on model calculations with orthogonal hybrid orbitals. However, closer inspection of the data in Table 2 reveals that s-character of the CH hybrid... 

FIGURE 3.18 The valence-bond description of the bonding in an ethane molecule, CjHf,. Only two of the bonds are shown in terms of their boundary surfaces. Each pair of neighboring atoms is linked by a cr-bond formed by the pairing of electrons in either Hls-orbitals or C2sp3 hybrid orbitals. All the bond angles are close to 109.5° (the tetrahedral angle). 

The three-dimensional structure of ethane, C2H6, has the shape of two tetrahedra joined together. Each carbon atom is sp3 hybridized, with four sigma bonds formed by the four sp3 hybrid orbitals. Dashed lines represent bonds that go away from the viewer, wedges represent bonds that come out toward the viewer, and other bond lines are in the plane of the page. All the bond angles are close to 109.5°. 

Rotation of single bonds. Ethane is composed of two methyl groups bonded by overlap of their sp3 hybrid orbitals. These methyl groups may rotate with respect to each other. 

Ethane, the two-carbon alkane, is composed of two methyl groups with overlapping sp3 hybrid orbitals forming a sigma bond between them. 

Each of the carbon-hydrogen sigma bonds is formed by overlap of an sp2 hybrid orbital on carbon with the Is orbital of a hydrogen atom. The C—H bond length in ethylene (1.08 A) is slightly shorter than the C—H bond in ethane (1.09 A) because the sp2 orbital in ethylene has more s character (one-third, v) than an sp3 orbital (one-fourth, v). The s orbital is closer to the nucleus than the p orbital, contributing to shorter bonds. 

Figure 1.12 The structure of ethane. The carbon-carbon bond is formed by a overlap of two carbon sp hybrid orbitals. For clarity, the smaller lobes of the sp hybrid orbitals are not shown.

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