Chapter 13 Unsaturated Hydrocarbons Saturated Hydrocarbons ...

Chapter 13 Unsaturated
Hydrocarbons
13.1 Alkenes and Alkynes
13.2 Naming Alkenes and Alkynes
13.3 Cis-Trans Isomers
Saturated Hydrocarbons
Saturated hydrocarbons:
• Have the maximum number of hydrogen
atoms attached to each carbon atom.
• Are alkanes and cycloalkanes with single
C-C bonds.
CH 3 —CH 2 —CH 3
1
2
Unsaturated Hydrocarbons
Unsaturated
hydrocarbons:
• Have fewer hydrogen
atoms attached to the
carbon chain than
alkanes.
• Are alkenes with
double bonds or
alkynes with triple
bonds.
Alkenes Have Double Bonds
In a double bond:
• One pair of electrons
form a strong sigma
(σ) bond.
• One pair of electrons
in adjacent p orbitals
overlap to form a pi
(π) bond.
3
4
Alkynes have Triple Bonds
Bond Angles in Alkenes and
Alkynes
In a triple bond:
• One pair of electrons
form a strong sigma
(σ) bond.
• Two pairs of
electrons in adjacent
p orbitals overlap to
form two pi (π)
bonds.
5
According to VSEPR
theory:
• The three groups bonded
to carbon atoms in a
double bond are at
angles of 120°.
• The two groups bonded
to each carbon in a triple
bond are at angles of
180°.
6
1

Naming Alkenes and Alkynes
• In the IUPAC system, the –ane ending of the
corresponding alkane is changed to –ene for
alkenes and to –yne for alkynes.
Naming Alkenes and Alkynes
When the carbon chain has 4 or more C
atoms, the chain is numbered to give the
lowest number to the double or triple bond.
1
CH 2 =CH—CH 2 —CH 3 1-butene
2
CH 3 —CH=CH—CH 2 —CH 3 2-pentene
3
CH 3 —CH 2 —C≡C—CH 2 —CH 3 3 -hexyne
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8
Learning Check
Write the IUPAC name for each:
A. CH 3 —CH 2 —C≡C—CH 3
CH 3
|
B. CH 3 —C=CH—CH 3 C.
Solution
Write the IUPAC name for each:
A. CH 3 —CH 2 —C≡C—CH 3
2-pentyne
CH 3
CH 3
|
B. CH 3 —C=CH—CH 3 C.
2-methyl-2-butene 3-methylcyclopentene
CH 3
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9
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.
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Cis-Trans Isomers
• Two isomers are possible
when 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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2

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.
Naming Cis-Trans Isomers
• The prefixes cis or trans are placed in front of the
alkene name when there are cis-trans isomers.
Br
H
C
C
Br
H
Br
H
C
C
H
Br
cis-1,2-dibromoethene
trans-1,2-dibromoethene
13
14
Cis-Trans Isomerism
Learning Check
• Alkenes cannot have cis-trans isomers if a
carbon atom in the double bond is attached
to identical groups.
Identical
H
Br
2-bromopropene
H
Identical
Br
C C
C C
H CH 3
H Br
1,1-dibromoethene
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Name each, using cis-trans prefixes when needed.
Br Br
A. C C
H H
CH 3 H
B. C C
H CH 3
CH 3 Cl
C. C C
H Cl
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Solution
Chapter 13 Unsaturated
Hydrocarbons
A.
Br
C
H
Br
C
H
cis-1,2-dibromoethene
13.4 Addition Reactions
B.
CH 3
C
H
C
H
CH 3
trans-2-butene
C.
CH 3
C
H
C
Cl
Cl
1,1-dichloropropene
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18
3

Addition Reactions
Hydrogenation
• The pi (π) bond is
easily broken, which
makes double and
triple bonds very
reactive.
• In the addition
reaction, reactants
are added to the
carbon atoms in the
double or triple bond.
19
• 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.
H H
H 2 C CH 2 +
Pt
H 2 C CH 2
H 2
HC CH + 2H 2
Ni
H
HC
H
H
CH
H
20
Hydrogenation of Oils
Learning Check
• When hydrogen
adds to the
double bonds in
vegetable oils, the
products are
solids at room
temperature.
Write the equation for the addition of
hydrogen to 1-butene using a Ni catalyst.
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22
Solution
Halogenation
Write the equation for the addition of
hydrogen to 1-butene using a Ni catalyst.
CH 2 =CH—CH 2 —CH 3 + H 2
Ni
• In halogenation, halogen atoms add to the
carbon atoms of a double bond or triple
bond.
Br Br
H 2 C CH 2 +
Br 2
H 2 C CH 2
Cl Cl
CH 3 —CH 2 —CH 2 —CH 3
HC C CH 3 + 2Cl H C C
2
Cl Cl
CH 3
23
24
4

Testing for Double and Triple
Bonds
• When bromine (Br 2 ) is
added to an alkane, the
red color of bromine
persists.
• When bromine (Br 2 ) is
added to an alkene or
alkyne, the red color of
bromine disappears
immediately.
Learning Check
Write the product of each addition reaction:
Pt
CH 2 =CH—CH 3 + H 2
+ Br 2
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26
Solution
Write the product of each addition reaction:
Pt
CH 2 =CH—CH 3 + H 2 CH 3 —CH 2 —CH 3
Br
Hydrohalogenation
• In hydrohalogenation, the atoms of a hydrogen
halide add to the carbon atoms of a double
bond or triple bond.
CH 3 CH CH CH 3 + HCl
CH 3 CH CH CH 3
H
H
Cl
+ Br 2
28
Br
+ HBr
Br
27
Markovnikov’s Rule
Hydration Adds Water
• When an unsymmetrical alkene undergoes
hydrohalogenation, the H in HX adds to the
carbon in the double bond that has the greater
number of H.
CH 3 CH CH 2 + HCl
H
Cl
CH 3 CH CH 2
Does not form
C with the most H
Cl H
CH 3 CH CH 2
Product that forms
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• In hydration, H and OH from water add to the
carbon atoms of a double bond or triple bond
to form alcohols (OH).
• The reaction is catalyzed by acid H + .
OH H
H +
CH 3 CH CH 2 + HOH CH 3 CH CH 2
+ HOH
H +
H
OH
30
5

Learning Check
Write the products of each reaction.
A. CH 3 CH CH 2 + Cl 2
Solution
Write the products of each reaction.
Cl Cl
A.
+ Cl 2
CH 3 CH CH 2
B.
CH 3 CH CH CH 3 + HOH
H +
B.
H +
CH 3 CH CH CH 3 + HOH
H
OH
CH 3 CH CH CH 3
C.
+ H 2
Pt
C.
CH 3 CH CH 2
H
+ H 2
Pt
H
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Chapter 13 Unsaturated
Hydrocarbons
13.5 Polymerization
Polymers
Polymers are:
• 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, Teflon, and nylon.
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34
Common Synthetic Polymers
Polymerization
• In polymerization, small repeating units called
monomers are bonded to form a long chain
polymer.
H
C
H
C
H
H
H
+ C C + C C
H
H
H
Ethylene monomers
H
H
H
H
chain continues
H
H
Repeating monomer
C C C C C C
H
H
H
H
H
H
H
H
H
H
chain continues
35
Polyethylene
36
6

Polymers from Addition Reactions
More Monomers and Polymers
37
38
Recycling Plastics
Learning Check
• 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
• What is the starting monomer for polyvinyl
chloride (PVC)
H Cl H Cl H Cl
C C C C C C
H
H
H
H
H
Polyvinyl chloride
H
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40
Solution
Chapter 13 Unsaturated
Hydrocarbons
• What is the starting monomer for polyvinyl
chloride (PVC)
H
C
C
Cl
H
Cl
H
+ C C + C C
Cl
13.6 Aromatic Compounds
H
H
H
H
H
H
Chloroethene monomers
41
42
7

Aromatic Compounds
Benzene is
• An aromatic compound.
• A ring of 6 C atoms and 6 H atoms.
• A flat ring structure drawn with double bonds.
• Represented by two structures because the
electrons move among the C atoms.
Benzene Structure
• Because the pi electrons in benzene are shared
equally among the 6 C atoms, benzene can
also be represented as a hexagon with a circle
drawn inside.
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44
Aromatic Compounds in Nature
and Medicine
Naming Aromatic Compounds
• A benzene with a single substituent is often
named as a benzene derivative.
CH 3
Cl
Methylbenzene
Chlorobenzene
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46
Some Common Names
• Some substituted benzene rings have common
names that have been in use for many years.
CH 3 NH 2 OH
Toluene Aniline Phenol
(Methylbenzene) (Benzenamine) (Hydroxybenzene)
47
Naming Aromatic Compounds
• A benzene ring with two or more substituents
is numbered to give the lowest numbers to the
side groups.
• Common names use the prefixes ortho- (1,2-),
meta- (1,3-) and para- (1,4-).
Br
Br
Cl
1,2-dimethylbenzene 1,3-dichlorobenzene 4-chloromethylbenzene
(o-dibromobenzene) (m-dichlorobenzene) (p-chlorotoluene)
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Cl
CH 3
Cl
8

Learning Check
Select the correct name for each structure:
Solution
Select the correct name for each structure:
Cl
1) chlorocyclohexane
2) chlorobenzene
3) 1-chlorobenzene
Cl
2) Chlorobenzene
Cl
Cl
1) 1,3-dichlorobenzene
2) o-dichlorobenzene
3) m-dichlorobenzene
Cl
Cl
1) 1,3-dichlorobenzene
3) m-dichlorobenzene
49
50
Learning Check
Write the structural formula for each:
A. 1-bromo-4-chlorobenzene
Solution
Write the structural formula for each:
Cl
A. 1-bromo-4-chlorobenzene
B. o-chlorotoluene
Br
B. o-chlorotoluene
CH 3
Cl
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Chapter 13 Unsaturated
Hydrocarbons
13.7 Properties of Aromatic Compounds
Benzene
H
+
Cl 2
FeCl 3
Cl
Chlorobenzene
+
HCl
Properties of Aromatic
Compounds
Aromatic compounds:
• Have a stable aromatic bonding system.
• Are resistant to many reactions.
• Undergo substitution reactions, which
retains the stability of the aromatic
bonding system.
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9

Substitution Reactions
In a substitution reaction, a hydrogen atom on
a benzene ring is replaced by an atom or group
of atoms.
Type of substitution H on benzene replaced by
• Halogenation chlorine or bromine atom
• Nitration nitro group (—NO 2 )
• Sulfonation
—SO 3 Hgroup
Halogenation
• Halogenation replaces a H on benzene by a
chlorine or bromine atom.
• A catalyst such as FeCl 3 is used in chlorination;
FeBr 3 in bromination.
Benzene
H
+
Cl 2
FeCl 3
Cl
Chlorobenzene
+
HCl
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56
Nitration
• Nitration replaces a H on benzene by a nitro
(—NO 2 ) group from HNO 3 .
• An acid catalyst such as H 2 SO 4 is used in
nitration.
Sulfonation
• Sulfonation replaces a H on benzene by a
—SO 3 H group from SO 3 .
• An acid catalyst such as H 2 SO 4 is used in
sulfonation.
H
NO 2
H
SO 3 H
+ HNO 3
H 2 SO 4
+
HOH
+
SO 3
H 2 SO 4
Benzene
Nitrobenzene
Benzene
Benzenesulfonic acid
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Learning Check
Write the equation for the bromination of
benzene, including catalyst.
Solution
Write the equation for the bromination of
benzene, including catalyst.
H
Br
+
Br 2
FeBr 3
+
HBr
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60
10