1. Naming Alkenes and Alkynes

2. Recall:

3. Alkenes General Formula = C n H 2n Contain one or more double bonds Names will end in “–ene” Alkynes General Formula = C n H 2n-2 Contain one or more triple bonds Names will end in “-yne”

4. Example #1 What is the formula of an alkene with 5 “C” atoms? Example #2 What is the formula of an alkyne with 10 “H” atoms?

6. Special Isomers for Alkenes: Cis and Trans Geometric isomers Remember that isomers are molecules with the same molecular formula with different arrangements of the atoms. Cis and Trans isomers (also called geometric isomers) occur when groups of atoms are arranged in different ways around a double bond.

7. Special Isomers for Alkenes: Cis and Trans Geometric isomers They occur because double bonds cannot rotate. This forces atoms attached to double bonded carbons to stay in the same position relative to one another.

8. In order to have cis and trans isomers, each carbon in the C=C double bond must have two different “groups” (also called substituents) attached to it. CH 3 and H are different groups (substituents) Special Isomers for Alkenes: Cis and Trans Geometric isomers

9. Cis isomers (or “Z” isomers) have the two larger substituents on the same side of the double bond. Trans isomers (or “E” isomers) have the two larger substituents on opposite sides of the double bond. (or Z-2-butene) (or E-2-butene) Special Isomers for Alkenes: Cis and Trans Geometric isomers

10. No cis or trans isomer because both substituents on carbon #2 are the same! 1 23 4

12. Steps for Naming Alkenes and Alkynes

13. Naming Alkenes and Alkynes Step 1: Identify the longest continuous chain of carbon atoms that contains the double or triple bond

14. Step 2: Use the smallest possible number to indicate the position of the double or triple bond. (Regardless of where branches are found!!) The location number goes in front of the parent chain alkene name. 1 23 4 5 6 7 3-heptene Naming Alkenes and Alkynes

15. Step 3: Name branches using same rules for alkane branches. 1 23 4 5 6 7 methyl 3-heptene Naming Alkenes and Alkynes

16. Step 4: Number the branches from the same end used to number the double/triple bond. 1 23 4 5 6 7 6-methyl 3-heptene Naming Alkenes and Alkynes

17. Step 5: (Alkenes only!!) Include “cis” or “trans” in front of the compound name if possible: *cannot have two of the same substituents on a carbon *must be able to see the shape in the diagram. 1 23 4 5 6 7 6-methyl 3-heptene “trans” (opposite sides) Naming Alkenes and Alkynes

18. Final Name: trans-6-methyl-3-heptene 1 23 4 5 6 7 6-methyl 3-heptene “trans” (opposite sides) Naming Alkenes and Alkynes

19. *Note: the trans / cis does not always exist or is not always possible to know! Possible to know the arrangement: Not Possible: Which side???? Naming Alkenes and Alkynes

20. cis-3-hexene Trans - Naming Alkenes and Alkynes cis-2-hexene

21. Sample #2: Provide the name for the following compound using IUPAC rules. Word file Naming Alkenes and Alkynes CH 2

22. Another example Word File Naming Alkenes and Alkynes

23. Practice makes perfect! Worksheet #5a *Fix questions!!

24. Sample Problem #3: Draw a condensed structural formula for the compound below: 3-butyl-5,7-dimethyl-1-hexyne Word File Word File Work Backwards through the name -Draw parent chain of carbons first (add H’s later) -Number the carbons -Add your branches Naming Alkenes and Alkynes