1. Unsaturated Hydrocarbons

2. Definiton A n unsaturated hydrocarbon is one which contains at least one double or triple bond between carbon atoms. T here are three kinds we will discuss: –A–Alkenes –A–Alkynes –A–Aromatics

3. Alkenes A lkenes have at least one double bond between carbon atoms.  bond  bond

4. Naming Alkenes A lkenes are named in a very similar manner to alkanes. T he same prefixes are used. R emove the –ane ending and replace it with –ene.

5. T he simplest alkene is ethene. I ts molecular formula is C 2 H 4.

6. Next… This is propene.

7. Four carbons or more…. T hings are a little bit more complicated when you have a four carbon alkene. T he name must identify where the double bond occurs, so the carbons are numbered.

8. The double bond on this molecule is located on the first carbon. This is named 1-butene.

9. The double bond on this molecule occurs at the second carbon. This is named 2-butene.

10. Notice a difference between these two molecules? These are known as geometric isomers. What is the difference?

11. Note how the ends of the molecule are on the SAME SIDE of the double bond. This is a cis- isomer of 2-butene. It is named cis-2-butene. Methyl groups on same side of double bond

12. Note how the ends of the molecule are on OPPOSITE sides of the double bond. This is a trans- isomer of 2-butene. It is named trans-2-butene. One methyl above double bond One methyl below double bond

13. What is the name of this alkene? Does it need a cis- or trans- designation? 1-pentene

14. trans-2-pentene cis-2-pentene

15. 1-hexene

16. trans-2-hexene

17. cis-2-hexene

18. trans-3-hexene cis-3-hexene

19. What about more than one double bond??? This is 2,4-hexdiene

20. And cyclic alkenes too???? cyclopropene

21. 1,3-cyclopentadiene!

22. trans-1-chloro-propene

23. 3-bromo-1,4-cyclohexadiene

24. 4-chloro-cis-2-pentene

25. This is an alkyne. It has a triple bond between the carbon atoms. Take the –ene ending from an alkene and change it to –yne. This is ethyne.

26. 2-butyne 1-butyne

27. What would you name this compound? 1,3,5-cyclohexatriene? Wouldn’t you like a name that’s a little easier on the brain?

28. This is benzene. It is often represented like this. Note the alternating double- single bonds.

29. Benzene is classified as an aromatic compound. Aromatic compounds have structures with alternating double and single bonds. Most contain a benzene ring. Here are a few you should recognize and KNOW:

30. Napthalene Anthracene (The main ingredient in mothballs.) One of the first identified carcinogens.

31. In the 1800’s, doctors in Great Britain noted a significant number of chimney sweeps developed scrotal cancer. The incidence of cancer was linked to exposure to the soot in chimneys. A major component of soot is anthracene.