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1
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Chapter 11 Unsaturated
Hydrocarbons
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11.1
Alkenes and Alkynes
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Copyright © 2009 by Pearson Education, Inc.
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2
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Saturated Hydrocarbons
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Saturated hydrocarbons
• have the maximum number of hydrogen atoms
attached to each carbon atom.
• are alkanes and cycloalkanes with single C-C
bonds.
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CH3—CH2—CH3
2
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3
Unsaturated Hydrocarbons
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Unsaturated hydrocarbons
• have fewer hydrogen
atoms attached to the
carbon chain than alkanes.
• are alkenes with double
bonds.
• are alkynes with triple
bonds.
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4
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Bond Angles in Alkenes and
Alkynes
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According to VSEPR theory:
• the three groups bonded to
carbon atoms in a double bond
are at 120° angles.
• alkenes are flat because the
atoms in a double bond all lie
in the same plane.
• the two groups bonded to each
carbon in a triple bond are at
180° angles.
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5
Naming Alkenes
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The names of alkenes
• use the corresponding alkane name.
• change the ending to –ene.
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Alkene
IUPAC
Common
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H2C=CH2
ethene
ethylene
H2C=CH─CH3
propene
propylene
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cyclohexene
5
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6
Ethene (Ethylene)
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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.
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7
Naming Alkynes
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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
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8
Naming Alkenes and Alkynes
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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
2
3
2
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4
3
2-butene
4
CH3─CH2─C≡C─CH3
5
4
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1-butene
CH3─CH=CH─CH3
1
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3
2
2-pentyne
1
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Guide to Naming Alkenes and
Alkynes
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10
Learning Check
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Write the IUPAC name for each of the following:
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1. CH2=CH─CH2─CH3
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2. CH3─CH=CH─CH3
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CH3
|
3. CH3─CH=C─CH3
4. CH3─C≡C─CH3
10
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11
Solution
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Write the IUPAC name for each of the following:
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1. CH2=CH─CH2─CH3 1-butene
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2. CH3─CH=CH─CH3
CH3
|
3. CH3─CH=C─CH3
2-butene
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4. CH3─C≡C─CH3
2-butyne
2-methyl-2-butene
11
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12
Learning Check
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Write the IUPAC name for each of the following:
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A. CH3─CH2─C≡C─CH3
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CH3
⎢
B. CH3─CH2─C=CH─CH3
12
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13
Solution
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Write the IUPAC name for each of the following:
A. CH3─CH2─C≡C─CH3
2-pentyne
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CH3
⎢
B. CH3─CH2─C=CH─CH3
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3-methyl-2-pentene
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14
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Chapter 11 Unsaturated
Hydrocarbons
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11.2
Cis-Trans Isomers
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Cis and Trans Isomers
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In an alkene, the double bond
• is rigid.
• holds attached groups in fixed positions.
• makes cis-trans isomers possible.
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16
Cis-Trans Isomers
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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.
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You can make a “double
bond” with your fingers with
both thumbs on the same
side or opposite from each
other.
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17
Cis-Trans Isomers
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Two isomers are possible when
groups are attached to the
double bond are different.
• In a cis isomer, the alkyl
groups are attached on the
one side of the double bond
and H atoms are on the other
side.
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• In the trans isomer, the
groups and H atoms are
attached on opposite sides.
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Cis-Trans Isomerism
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• Alkenes cannot have cis-trans isomers if a carbon
atom in the double bond is attached to identical
groups.
Identical
HH
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Identical
Br
H
Br
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Br
H
C C
HH
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C C
CH3
2-Bromopropene
(not cis or trans)
H
Br
1,1-Dibromoethene
(not cis or trans)
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Cis-Trans Isomers in Nature
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• Insects emit tiny quantities of pheromones, which are
chemicals that send messages.
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• The silkworm moth attracts other moths by emitting
bombykol, which has one cis and one trans double
bond.
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20
Naming Cis-Trans Isomers
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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
Br
Br
H
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H
Br
C C
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C C
H
H
cis-1,2-Dibromoethene
Br
trans-1,2-Dibromoethene
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Learning Check
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Name each, using cis-trans prefixes when needed.
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Br
Br
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C C
A.
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H
H
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H
CH3
C C
B.
H
CH3
Cl
CH3
C.
C C
H
Cl
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22
Solution
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Br
Br
C C
A.
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cis-1,2-Dibromoethene
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H
H
trans-2-Butene
C C
B.
H
CH3
Cl
CH3
C.
C C
H
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H
CH3
1,1-Dichloropropene
Cl
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23
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Chapter 11 Unsaturated
Hydrocarbons
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11.3
Addition Reactions
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24
Addition Reactions
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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.
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25
Hydrogenation
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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.
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H H
H2C CH2 + H2
Pt
H2C CH2
H H
HC CH + 2H2
Ni
HC CH
H H
25
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26
Hydrogenation of Oils
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Adding H2 to double
bonds in vegetable
oils produces
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•
compounds with higher
melting points.
• solids at room
temperature, such as
margarine,
soft margarine,
and shortening.
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26
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27
Learning Check
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Write an equation for the hydrogenation of 1-butene
using a platinum catalyst.
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27
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28
Solution
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Write an equation for the hydrogenation of 1-butene using
a platinum catalyst.
Pt
CH2=CH─CH2─CH3 + H2
CH3─CH2─CH2─CH3
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28
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29
Trans Fats
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In vegetable oils, the unsaturated fats usually contain
cis double bonds.
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• During hydrogenation, some cis double bonds are
converted to trans double bonds (more stable),
causing a change in the fatty acid structure.
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• If a label states “partially” or “fully hydrogenated,” the
fats contain trans fatty acids.
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Learning Check
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(1) True or (2) False
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A.____ There are more unsaturated fats in vegetable oils
than in animal fats.
B. ____ Hydrogenation converts some cis-double bonds to
trans-double bonds.
C. ____ Animal fats have more unsaturated fats than
vegetable oils.
30
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Solution
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(1) True or (2) False
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A.__1_ There are more unsaturated fats in vegetable
oils than in animal fats.
B. __1_ Hydrogenation converts some cis-double bonds
to trans-double bonds.
C. __2_ Animal fats have more unsaturated fats than
vegetable oils.
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31
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Learning Check
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Write the product of each the following:
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Pt
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CH3─CH=CH─CH3 + H2
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Pt
+ H2
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Solution
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Pt
1. CH3─CH=CH─CH3 + H2
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CH3─CH2─CH2─CH3
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Pt
2.
+ H2
33
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34
Hydration
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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
CH3─CH=CH─CH3 + H─OH
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35
Hydration
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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
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36
Learning Check
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Write the product for the hydration of each of the
following:
H+
1. CH3─CH2─CH=CH─CH2─CH3 + HOH
CH3
│
H+
2. CH3─C=CH─CH2─CH3 + HOH
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H+
3.
+ HOH
36
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37
Solution
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1.
2.
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H OH
│
│
CH3─CH2─CH─CH─CH2─CH3
CH3
│
CH3─C─CH─CH2─CH3
│ │
OH H
OH
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3.
H
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38
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Chapter 11 Unsaturated
Hydrocarbons
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11.4
Polymers of Alkenes
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Copyright © 2009 by Pearson Education, Inc.
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Polymers
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Polymers are
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• large, long-chain molecules.
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• found in nature, including cellulose in plants,
starches in food, proteins, and DNA in the body.
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• also synthetic, such as polyethylene and
polystyrene, TeflonTM, and nylon.
• composed of small repeating units called
monomers.
• made from reaction of small alkenes.
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Common Synthetic Polymers
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Common Synthetic Polymers
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Common Synthetic Polymers
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Polymerization
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In polymerization, small repeating units called monomers
join to form a long chain polymer.
H
H
+
C C
H
H
H
H
C C
H
H
+
H
H
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monomer unit repeats
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C C
H
H
Ethylene monomers
chain continues
H H H
H H H
C C C
C C C
chain continues
H H H
H H H
n
Polyethylene
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Polymers from Addition Reactions
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44
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More Monomers and Polymers
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Learning Check
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What is the starting monomer for polyethylene?
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46
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Solution
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Ethene (ethylene)
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CH2=CH2
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Learning Check
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Name the monomer used to make Teflon, and write a
portion of a Teflon polymer using four monomers.
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48
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49
Solution
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F F
│
___________________________________
│
F─C=C─F
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tetrafluoroethene
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F
F F
F F F F F
│
│
│
│
│
│
│ │
│
│
│
│
│
│
│ │
F
F F
─C─C─C─C─C─C─C─C─
___________________________________
portion of Teflon
F F F F F
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50
Recycling Plastics
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Recycling is simplified by using codes on plastic items.
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1
2
3
4
5
6
7
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PETE Polyethyleneterephtalate
HDPE High-density polyethylene
PV Polyvinyl chloride
LDPE Low-density polyethylene
PP Polypropylene
PS Polystyrene
OTHER Other plastic: fiberglass, polycarbonate, etc.
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Learning Check
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What types of plastic are indicated by the following
codes?
A.
B.
___________________________________
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3
PV
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5
PP
C.
6
PS
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Solution
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What types of plastic are indicated by the following
codes?
A.
B.
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3
PV
Polyvinyl chloride
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Polypropylene
5
PP
C.
.
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Polystyrene
6
PS
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53
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Chapter 11 Unsaturated
Hydrocarbons
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11.5
Aromatic Compounds
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Aromatic Compounds
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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.
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Benzene Structure
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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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Aromatic Compounds in Nature and
Health
O
Vanillin
Aspirin
CH
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O
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COH O
___________________________________
C O CH3
___________________________________
OCH3
O
OH
Ibuprofen
Acetaminophen
NH C CH3
CH3 O
CH3
CH COH
H3C CH CH2
OH
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Naming Aromatic Compounds
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Aromatic compounds are named
• with benzene as the parent chain.
• with one side group named in front of benzene.
CH3
Methylbenzene
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Cl
Chlorobenzene
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Some Common Names
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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.
Toluene
(methylbenzene)
Aniline
(benzenamine)
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___________________________________
OH
NH2
CH3
___________________________________
Phenol
(hydroxybenzene)
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Naming Aromatic Compounds
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When two groups are attached to the benzene ring, the
ring is numbered to give the lowest numbers to the side
groups.
Cl
CH3
___________________________________
___________________________________
OH
___________________________________
Cl
Cl
3-Chlorotoluene
Cl
1,4-Dichlorobenzene
2-Chlorophenol
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Learning Check
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___________________________________
___________________________________
Select the correct name for each compound.
Cl
1) chlorocyclohexane
2) chlorobenzene
3) 1-chlorobenzene
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___________________________________
___________________________________
1) 1,2-dimethylbenzene
2) 1,4-dimethylbenzene
3) 1,3-dimethylbenzene
CH3
CH3
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Solution
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___________________________________
___________________________________
Select the correct name for each compound.
___________________________________
Cl
2) chlorobenzene
___________________________________
___________________________________
CH3
3) 1,3-dimethylbenzene
CH3
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Learning Check
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___________________________________
___________________________________
Write the structural formulas for each of the following:
A. 1,3-dichlorobenzene
___________________________________
___________________________________
___________________________________
B. 2-chlorotoluene
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Solution
___________________________________
___________________________________
___________________________________
Write the structural formulas for each of the following:
A. 1,3-dichlorobenzene
Cl
___________________________________
___________________________________
___________________________________
Cl
B. 2-chlorotoluene
CH3
Cl
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Learning Check
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___________________________________
___________________________________
Identify the organic family for each:
___________________________________
A. CH3─CH2─CH=CH2
___________________________________
___________________________________
B.
C. CH3─C≡CH
D.
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Solution
___________________________________
___________________________________
___________________________________
Identify the organic family for each:
___________________________________
A. CH3─CH2─CH=CH2
alkene
B.
cycloalkane (alkane)
C. CH3─C≡CH
alkyne
D.
aromatic
___________________________________
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