1. Chemeketa Community College
Chapter 11:
Unsaturated
Hydrocarbons
Larry Emme
Chemeketa Community College

2. Chapter Outline Alkenes & Alkynes Cis-Trans Isomers Reactions Polymers
Aromatic Compounds

3. Saturated Hydrocarbons
have the maximum number of hydrogen atoms attached to each carbon atom.
are alkanes and cycloalkanes with single C-C bonds.
CH3—CH2—CH3

4. Unsaturated Hydrocarbons
have fewer hydrogen atoms attached to the carbon chain than alkanes.
are alkenes or olefins with double bonds.
are alkynes or acetylenes with triple bonds.
First member of each family
must have two carbons

5. 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

6. Ethene (Ethylene) Ethene, or ethylene,
is an alkene with the formula 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.
Copyright © by Pearson Education, Inc.

7. 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

8. Naming Alkenes and Alkynes
When the carbon chain of an alkene or alkyne has four or more C atoms, number the chain to give the lowest number to the first carbon in the double or triple bond.
CH2=CH─CH2─CH3 1-butene
CH3─CH=CH─CH3 2-butene
CH3─CH2─CC─CH3 2-pentyne

9. Guide to Naming Alkenes and Alkynes

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

11. Learning Check Answers
Write the IUPAC name for each of the following:
1. CH2=CH─CH2─CH3
2. CH3─CH=CH─CH3
CH3 |
3. CH3─CH=C─CH3
4. CH3─CC─CH3
1-butene
2-butene
2-methyl-2-butene
2-butyne

12. Learning Check Write the IUPAC name for each of the following:
A. CH3─CH2─C≡C─CH3
B. CH3─CH2─C=CH─CH3
CH3 

13. Learning Check Answers
Write the IUPAC name for each of the following:
A. CH3─CH2─C≡C─CH3
B. CH3─CH2─C=CH─CH3
2-pentyne
CH3 
3-methyl-2-pentene

14. Name this compound: Learning Check
Write the IUPAC name for the following:

15. Name this compound: Learning Check Answers
ethyl 3 5 2 4 1
Longest chain containing C=C is 5 carbons
2-ethyl-1-pentene

16. Fragrant Alkenes

17. Cis-Trans Isomers 17

18. Cis and Trans Isomers In an alkene, the double bond is rigid.
holds attached groups in fixed positions.
makes cis-trans isomers possible.
cis-2-butene
trans-2-butene 18

19. Trans is a Latin noun or prefix, meaning “across”, “beyond” or “on the opposite side”.
Cis is a Latin prefix, meaning “on the same side [as]” , “on this side [of]”, or “near side [of]”. 19

20. Cis-Trans Isomers In cis-trans isomers
there is no rotation around the double bond in alkenes.
groups attached to the double bond are fixed relative to each other.
You can make a “double bond” with your fingers with both thumbs on the same side or opposite from each other. 20

21. Cis-Trans Isomerism
Alkenes cannot have cis-trans isomers if a carbon atom in the double bond is attached to identical groups.
Identical Identical
2-Bromopropene ,1-Dibromoethene
(not cis or trans) (not cis or trans) H Br H H 21

22. Cis-Trans Isomers in Nature
Insects emit tiny quantities of pheromones, which are chemicals that send messages.
The silkworm moth attracts other moths by emitting bombykol, which has one cis and one trans double bond. 22

23. Naming Cis-Trans Isomers
The prefix of cis or trans is placed in front of the alkene name when the compound is a cis or trans isomer.
cis trans
cis-1,2-Dibromoethene trans-1,2-Dibromoethene 23

24. Is the compound below the cis or trans isomer?
Learning Check
Is the compound below the cis or trans isomer?

25. Is the compound below the cis or trans isomer?
Learning Check Answers
Is the compound below the cis or trans isomer? 1 2 3 4 5
trans-3-methyl-2-pentene

26. Other Alkenes
ter
ter
Samantha H C C C C H H H
Ashley

27. Learning Check
Name each, using cis-trans prefixes when needed. 27

28. Learning Check Answers
cis-1,2-Dibromoethene 1
trans-2-Butene 4 3
1,1-Dichloropropene 28

29. Addition Reactions 29

30. Addition Reactions In alkene and alkynes,
the double or triple bond is easily broken, which makes double and triple bonds very reactive.
in addition reactions, reactants are added to the carbon atoms in the double or triple bond. 30

31. Addition of X2 Halogenation In halogenation,
halogen atoms such as chlorine or bromine are added to the carbon atoms of a double bond.
the reaction occurs rapidly, without the use of a catalyst.

32. Addition of X2
Halogenation
Examples

33. Addition of X2 The addition reaction of bromine
is used to test for the presence
of double bonds.
When bromine is added to an alkane
in the first test tube, the orange color
of bromine remains because the alkane
does not react.
When bromine is added to an alkene in the
second test tube, the orange color quickly
disappears as bromine atoms add to the
double bond to give colorless products.

34. Hydrogenation In hydrogenation,
hydrogen atoms add to the carbon atoms of a double bond or triple bond.
a catalyst such as Pt or Ni is used to speed up the reaction. 34

35. Hydrogenation of Oils Adding H2 to double bonds in vegetable
oils produces
compounds with higher melting points.
solids at room temperature, such as margarine,
soft margarine,
and shortening. 35

36. Reaction Example
Write an equation for the hydrogenation of 1-butene using
a platinum catalyst. Pt
CH2=CH─CH2─CH3 + H CH3─CH2─CH2─CH3 36

37. Trans Fats In vegetable oils, the unsaturated fats usually contain
cis double bonds.
During hydrogenation, some cis double bonds are converted to trans double bonds (more stable), causing a change in the fatty acid structure.
If a label states “partially” or “fully hydrogenated,” the fats contain trans fatty acids. 37

38. Learning Check Write the product of each the following: Pt
CH3─CH=CH─CH3 + H2
+ H2 38

39. Learning Check AnswersPt
1. CH3─CH=CH─CH3 + H CH3─CH2─CH2─CH3 H2 39

40. Hydration In the addition reaction called hydration,
an acid H+ catalyst is required.
water (HOH) adds to a double bond.
an H atom bonds to one C in the double bond.
an OH bonds to the other C.
H OH
H │ │
CH3─CH=CH─CH3 + H─OH CH3─CH─CH─CH3 40

41. Hydration When hydration occurs with a double bond that has an
unequal number of H atoms,
the H atom bonds to the C in the double bond with the more H.
the OH bonds to the C in the double bond with the fewer H atoms.
OH H
H │ │
CH3─CH=CH2 + H─OH CH3─CH─CH2
C has 1 H
C has 2 H’s
Them that has, gets! 41

42. Learning Check Write the product for the hydration of each of the
following: H+
1. CH3─CH2─CH=CH─CH2─CH HOH
CH3
│ H+
2. CH3─C=CH─CH2─CH HOH
HOH 42

43. Learning Check Answers
H OH
│ │
1. CH3─CH2─CH─CH─CH2─CH3
CH3 │
2. CH3─C─CH─CH2─CH3
│ │
OH H OH 3. H 43

44. Polymers of Alkenes 44

45. Polymers Polymers are large, long-chain molecules.
Synthetic polymers are
used to replace diseased
veins and arteries.
Polymers are
large, long-chain molecules.
found in nature, including cellulose in plants, starches in food, proteins, and DNA in the body.
also synthetic, such as polyethylene and polystyrene, TeflonTM, and nylon.
composed of small repeating units called monomers.
made from reaction of small alkenes. 45

46. Common Synthetic Polymers46

47. Common Synthetic Polymers47

48. Common Synthetic Polymers48

49. Polymerization
In polymerization, small repeating units called monomers join to form a long chain polymer.
monomer unit repeats n 49

50. Polymers from Addition Reactions50

51. More Monomers and Polymers51

52. Recycling Plastics
Recycling is simplified by using codes on plastic items.
1 PETE Polyethyleneterephtalate
2 HDPE High-density polyethylene
3 PV Polyvinyl chloride
4 LDPE Low-density polyethylene
5 PP Polypropylene
6 PS Polystyrene
7 OTHER Other plastic: fiberglass, polycarbonate, etc. 52

53. Aromatic Compounds 53 53

54. Benzene, or benzol, is an compound with the molecular formula C6H6
Benzene, or benzol, is an compound with the molecular formula C6H6. It is sometimes abbreviated Ph–H.
Michael Faraday (1791 –1867 ) first isolated and identified benzene in 1825 from the oily residue derived from the production of illuminating gas, giving it the name bicarburet of hydrogen.
1820
The empirical formula for benzene was long known, but its highly polyunsaturated structure, with just one hydrogen atom for each carbon atom, was challenging to determine. Several in 1861 suggested possible structures that contained multiple double bonds or multiple rings, but the study of aromatic compounds was in its very early years, and too little evidence was then available to help chemists decide on any particular structure.
6 bonds ?

55. Friedrich Auguste Kekulé

56. Aromatic Compounds Benzene is an aromatic compound.
a ring of 6 C atoms and 6 H atoms.
a flat ring structure drawn with three double bonds.
represented by two structures because the electrons are shared among all the C atoms. 56 56

57. Benzene Structure Benzene
has 6 electrons shared equally among the 6 C atoms.
is also represented as a hexagon with a circle drawn inside. 57 57

58. Aromatic Compounds in Nature and Health
Vanillin Aspirin
Ibuprofen Acetaminophen 58 58

59. Naming Aromatic Compounds
Aromatic compounds are named
with benzene as the parent chain.
with one side group named in front of benzene.
Methylbenzene Chlorobenzene 59 59

60. Some Common Names Some substituted benzene rings
have common names that have been in use for many years.
with a single substituent use a common name or are named as a benzene derivative. 60 60

61. Naming Aromatic Compounds
When two or more groups are attached to the benzene ring, the ring is numbered to give the lowest numbers to the side groups. 1 1 1 2 3 4 61 61

62. Naming Aromatic Compounds
When a common name such as aniline, phenol, or toluene can be used, the carbon atom attached to the amine, hydroxyl, or methyl group is numbered as carbon #1. Then the modifiers are named alphabetically. 1 1 1 2 2 2 6 3 3 5 3 4 4 62 62

63. Aromatic Compounds with Two Substituents
The position of the two groups can be indicated by numbering the ring carbons, or by using the designations in the figure at left.

64. Examples of naming with two groups:1 3 1 1 2
1,3-dichlorobenzene
(meta-dichlorobenzene or
m-dichlorobenzene) 4
2-bromotoluene
(ortho-bromotoluene or
o-bromotoluene)
1,3 = meta
1-bromo-4-chlorobenzene
(para-bromochlorobenzene or
p-bromochlorobenzene)
1,2 = ortho
1,4 = para

65. Learning Check
The correct name for each compound is. 65 65

66. Learning Check Answers
The correct name for each compound is.
chlorobenzene
1,3-dimethylbenzene
(meta-dimethylbenzene) 66 66

67. Learning Check
Write the structural formulas for each of the following:
A. 1,3-dichlorobenzene
B. ortho-chlorotoluene 67 67

68. Learning Check Answers
Write the structural formulas for each of the following:
A. 1,3-dichlorobenzene
B. ortho-chlorotoluene 68 68

69. Polycyclic Aromatic Hydrocarbons PAHs
mothballs
dyes
carcinogen
Product of combustion of coal tar, tobacco smoke, barbecued meats.
Potent carcinogen

70. The End

71. End of Chapter Learning Checks Try these after you have reviewed the chapter

72. Learning Check
What is the structural formula of 4-methyl-2-pentene?

73. Learning Check Answers
What is the structural formula of 4-methyl-2-pentene?
The name indicates:
Five carbons in the longest chain containing the double bond.
The double bond is between carbons #2 and #3
A methyl group is on carbon #4.

74. Learning Check Draw the chemical structure of cis-5-chloro-2-hexene.

75. Learning Check Answers
Draw the chemical structure of cis-5-chloro-2-hexene.
This molecule contains six carbons with a C=C between carbons #2 and #3, and a Cl atom on carbon #5.

76. Learning Check Answers
Draw the chemical structure of cis-5-chloro-2-hexene.
This molecule is also cis because the carbon atoms in the longest chain containing the double bond are on the same side of the double bond.

77. Learning Check
Is this the cis or trans isomer of 3-methyl-2-pentene?

78. Learning Check Answers
Is this the cis or trans isomer of 3-methyl-2-pentene?
This is trans-3-methyl-2-pentene because the carbon atoms in the longest chain are on opposite sides of the double bond.

79. Learning Check
Name the following compound.

80. Learning Check Answers
Name the following compound.
1-bromo-4-methylcyclohexene

81. Learning Check
Name the following compounds.

82. Learning Check Answers
Name the following compounds.
3-methyl-1-butyne
1-chloro-2-butyne

83. Learning Check
Name the following compounds.

84. Learning Check Answers
Name the following compounds.
1-chloro-2-bromo-4-nitrobenzene
1-ethyl-2-fluorobenzene or
ortho-ethylfluorobenzene
3-nitrotoluene or
meta-nitrotoluene

85. Learning Check
What are some common uses of polyethylene? 85 85

86. Learning Check Answers
What are some common uses of polyethylene?
Packing materials, molded articles, plastic films, garbage bags, flexible bottles, containers and toys. 86 86

87. Learning Check
What does the “PP” stand for in the symbol below? 87 87

88. Learning Check Answers
What does the “PP” stand for in the symbol below?
This is the identification code for polypropylene. “PP” stands for polypropylene. 88 88

89. Learning Check
What does the “PS” stand for in the symbol below? 89 89

90. Learning Check Answers
What does the “PS” stand for in the symbol below?
This is the identification code for polystyrene. “PS” stands for polystyrene. 90 90