The Paraffins Localized Bonds

The paraffins (four of which are shown below) are hydrocarbons represented classically by structures in which each carbon atom is linked to four neighbors by single bonds and each hydrogen to one neighbor, and in 

FIGURE 1.28. (a) Representation of ethane in terms of hybrid AOs (b) unperturbed MOs for a paraffin (c) effect of first-order perturbations (d) effect of bonding CC-bonding CH interactions (e) effect of bonding-antibonding interactions. 

In ethylene, C2H4, the atoms lie in a plane as indicated in Fig. 1.29(a). The MOs must be symmetric or antisymmetric for reflection in this plane. With the choice of coordinates indicated, it is obvious that all the AOs are symmetric except the 2p AOs of the carbon atoms. These will combine to form a bonding-antibonding pair of n MOs, just as in the diatomic molecules of Section 1.10. 

The three remaining AOs of each carbon atom can now be replaced by three equivalent hybrid AOs. With the geometry indicated in Fig. 1.29(b), 

FIGURE L29. (a) Geonieiry of ethylene (b) jtp hybrid AOs formed from AOs j, x, and y (c) localized bond representation of x MOs in ethylene 

---