8. Why are cyclopropane and cyclobutane termed strained molecules? Sketch the molecular-orbital picture of cyclopropane and account for the strain.

9. Why is the chair conformation of cyclohexane more stable than the boat form?

10. What is an alkene? An alkyne?

11. How are alkene molecules constrained, in a way that alkanes are not?

12. What is the systematic name for isobutylene? What do the numbers in 1-butene and 2-butene signify? Why is there no 3-butene?

13. What is the distinction between- structural and geometric isomers? Are 1-butene and 2-butene structural, or geometric, isomers?

14. Draw the structures of cis- and trans-2-butene. Are they structural, or geometric, isomers?

15. How do the structures of the isomers of C,H10 affect their physical properties?