27. Use the sp3 model and then the sp2 model to predict what would happen to the double bond when the two ends of the ethylene molecule are twisted9 How does the real molecule behave, and which model is most compatible with reality?

28. Sketch the o--bond skeleton of the ethylene molecule. Draw in the p MO of the second bond. What is the electron probability density at each of the six atoms in ethylene from the electrons in this p MO? Draw the nodal surface for this orbital.

29. Sketch the s-bond skeleton of the acetylene molecule. Draw in the p MO's of the second and third bonds between carbon.

30. How does the carbon-carbon bond length change between ethane, ethylene, and acetylene? How would you expect the bond energies to change?

31. Sketch the s-bond skeleton of the benzene molecule. How many AO's and how many bonding electrons are used in this s- skeleton? What kind of hybridization is used around the carbon atoms?