1. Chapter 12 Unsaturated Hydrocarbons
12.1
Alkenes and Alkynes
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2. Unsaturated Hydrocarbons
• Have fewer hydrogen atoms attached to the carbon chain than alkanes.
• Are alkenes with double bonds.
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• Are alkynes with triple bonds.

3. Bond Angles in Alkenes and Alkynes
According to VSEPR theory:
• Three groups in a double bond are bonded at 120° angles.
• Alkenes are flat, because the atoms in a double bond lie in the same plane.
• The groups attached to a triple bond are at 180°
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angles.

4. Naming Alkenes The names of alkenes
• Use the corresponding alkane name.
• Change the ending to -ene.
Alkene
IUPAC
Common
H2C=CH2
ethene
ethylene
H2C=CH ─CH3
propene
propylene
cyclohexene

5. Ethene (ethylene) Ethene or ethylene • Is an alkene C2H4.
• Has two carbon atoms
connected by a double bond.
• Has two H atoms bonded to each C atom.
• Is flat with all the C and H atoms in the same plane.
• Is used to accelerate the
ripening of fruits.
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6. Naming Alkynes The names of alkynes
• Use the corresponding alkane name.
• Change the ending to -yne.
Alkyne
IUPAC
Common
HC ≡CH
ethyne
acetylene
HC ≡C ─CH3
propyne

7. Guide to Naming Alkenes and Alkynes
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8. Naming Alkenes Write the IUPAC name for CH2=CH ─CH2 ─CH3 and
STEP 1 Name the longest carbon chain butene
STEP 2 Number the chain from the double bond CH2=CH ─CH2 ─CH3 1-butene 1 2 3 4
CH3 ─CH=CH ─CH3
2-butene

9. Comparing Names of Alkanes, Alkenes, and Alkynes
TABLE 12.1
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10. Naming Alkenes with Substituents
CH3 │
Write the IUPAC name for CH3 ─CH ─CH=CH ─CH3
STEP 1 Name the longest carbon chain
pentene
STEP 2 Number the chain from the double bond
CH3 │
CH3 ─CH ─CH=CH ─CH3
2-pentene 5 4 3 2 1
STEP 3 Give the location of each substituent 4-methyl- 2-pentene

11. Naming Alkynes with Substituents
CH3 │
Write the IUPAC name for HC ≡C ─CH ─CH3 1 2 3 4
STEP 1 Name the longest carbon chain
butyne
STEP 2 Number the chain from the double bond 1-butyne
STEP 3 Give the location of each substituent 3-methyl-1-butyne

12. Learning Check Write the IUPAC name for each of the following:
1. CH2=CH ─CH2 ─CH3
2. CH3 ─CH=CH ─CH CH3 |
3. CH3 ─CH=C ─CH3
4. CH3 ─C ≡C ─CH3

13. Solution Write the IUPAC name for each of the following:
1. CH2=CH ─CH2 ─CH3
1-butene
2. CH3 ─CH=CH ─CH3
2-butene
CH3 |
3. CH3 ─CH=C ─CH3
2-methyl-2-butene
4. CH3 ─C ≡C ─CH3
2-butyne

14. Learning Check Write the structural formula for each of the following:
2-pentyne B.
3-methyl-2-pentene

15. Solution Write the structural formula for each of the following: A.
CH3 ─CH2 ─C ≡C ─CH3
2-pentyne
CH3 |
B. CH3 ─CH2 ─C=CH ─CH3
3-methyl-2-pentene

16. Chapter 12 Unsaturated Hydrocarbons
12.2
Cis-Trans Isomers
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17. Cis and Trans Isomers
In an alkene, cis and trans isomers are possible because the double bond
• Is rigid.
• Cannot rotate.
• Has groups attached to the carbons of the double bond that are fixed relative to each other.
CH3
CH3
CH3
CH = CH
CH = CH
cis
trans CH3

18. Cis-Trans Isomers Cis-trans isomers
• Can be modeled by making a “double bond” with your fingers with both thumbs on the same side or opposite
from each other.
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19. Cis-Trans Isomers
Cis-trans isomers occur when different groups are attached to the double bond.
• In a cis isomer, groups are attached on the same side of the double bond.
• In the trans isomer, the groups are attached on opposite sides.
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20. Cis-Trans Isomerism H Br C C C C H CH3 Br
• Cis-trans isomers do not occur if a carbon atom in the double bond is attached to identical groups.
Identical
Identical H Br H Br
C C
C C H
CH3 Br H
2-bromopropene
1,1-dibromoethene
(not cis or trans)
(not cis or trans)

21. Naming Cis-Trans Isomers
• The prefixes cis or trans are placed in front of the alkene name when there are cis-trans isomers.
cis
trans
Br Br
Br H
C C
C C
H Br
H H
cis-1,2-dibromoethene
trans-1,2-dibromoethene

22. Pheromones A pheromone
• Is a chemical messenger emitted by insects in tiny quantities.
• Called bombykol emitted by the silkworm moth to attract other moths has one cis and one trans double
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23. Learning Check Name each, using cis-trans prefixes when needed. Br Br
C C H H
CH3 H B.
C C H
CH3
CH3 Cl C.
C C H Cl

24. Solution cis-1,2-dibromoethene trans-2-butene 1,1-dichloropropene Br
C C
cis-1,2-dibromoethene H H
CH3 H B.
C C
trans-2-butene H
CH3
CH3 Cl C.
C C H Cl
1,1-dichloropropene
Identical atoms on one C; no cis or trans

25. Chapter 12 Unsaturated Hydrocarbons
12.5
Aromatic Compounds
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26. Benzene Structure Benzene
• Has 6 electrons shared equally among the 6 C atoms.
• Is also represented as a hexagon with a circle drawn inside.
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27. Aromatic Compounds in Nature and Health
Vanillin O
Aspirin O CH
COH O
C O CH3
OCH3 O OH
NH C CH3
Ibuprofen
Acetaminophen
CH3
CH3 O
HC CH
CH2 CH COH OH 3

28. Naming Aromatic Compounds
Aromatic compounds are named
• With benzene as the parent chain.
• With one side group named in front of benzene.
CH3 Cl
methylbenzene
chlorobenzene

29. Some Common Names Some substituted benzene rings
• Have common names used for many years.
• With a single substituent use a common name or are named as a benzene derivative.
CH3
NH2 OH
toluene
aniline
phenol
(methylbenzene)
(benzenamine)
(hydroxybenzene)

30. Learning Check Identify the organic family for each:
A. CH3 ─CH2 ─CH=CH2 B.
C. CH3 ─C ≡CH D.

31. Solution Identify the organic family for each: A. CH3 ─CH2 ─CH=CH2
alkene B.
cycloalkane (alkane)
C. CH3 ─C ≡CH
alkyne D.
aromatic