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Chapter 13
Alkanes, Alkynes, and
Aromatic Compounds
1
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.
CH3—CH2—CH3
2
13.1 Alkenes and Alkynes
 Unsaturated
hydrocarbons:
 Have fewer hydrogen
atoms attached to the
carbon chain than
alkanes.
 Are alkenes with
double bonds or
alkynes with triple
bonds.
3
Alkenes Have Double Bonds
In a double bond:
 One pair of electrons
form a strong sigma
() bond.
 One pair of electrons
in adjacent p orbitals
overlap to form a pi
() bond.
4
Alkynes have Triple Bonds
In a triple bond:
 One pair of electrons
form a strong sigma
() bond.
 Two pairs of electrons
in adjacent p orbitals
overlap to form two
pi () bonds.
5
Bond Angles in Alkenes and
Alkynes


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
13.2 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.
7
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
CH2=CH—CH2—CH3
1-butene
2
CH3—CH=CH—CH2—CH3
2-pentene
3
CH3—CH2—CC—CH2—CH3 3 -hexyne
8
Learning Check
Write the IUPAC name for each:
A. CH3—CH2—CC—CH3
CH3
|
B. CH3—C=CH—CH3
CH3
C.
9
Solution
Write the IUPAC name for each:
A. CH3—CH2—CC—CH3
2-pentyne
CH3
|
B. CH3—C=CH—CH3
2-methyl-2-butene
CH3
C.
3-methylcyclopentene
10
13.3 The Structure of Alkenes: Cis-Trans
Isomerism
 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.
11
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.
12
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.
13
Naming Cis-Trans Isomers

The prefixes cis or trans are placed in front of the
alkene name when there are cis-trans isomers.
Br
Br
C C
H
H
Br
C C
H
cis-1,2-dibromoethene
H
Br
trans-1,2-dibromoethene
14
Cis-Trans Isomerism

Alkenes cannot have cis-trans isomers if a carbon
atom in the double bond is attached to identical
groups.
Identical
H
Br
H
C C
H
Identical
Br
C C
CH3
2-bromopropene
H
Br
1,1-dibromoethene
15
Learning Check
Name each, using cis-trans prefixes when needed.
Br
Br
C C
A.
H
H
H
CH3
C C
B.
H
CH3
Cl
CH3
C.
C C
H
Cl
16
Solution
Br
Br
cis-1,2-dibromoethene
C C
A.
H
H
H
CH3
trans-2-butene
C C
B.
H
CH3
Cl
CH3
C.
1,1-dichloropropene
C C
H
Cl
17
13.4 Properties of Alkenes and
Alkynes
13.4 Addition Reactions
18
Addition Reactions
 The pi () 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
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.
H H
H2C CH2 + H2
Pt
H2C CH2
H H
HC CH + 2H2
Ni
HC CH
H H
20
Hydrogenation of Oils
 When hydrogen
adds to the
double bonds in
vegetable oils,
the products are
solids at room
temperature.
21
Learning Check
Write the equation for the addition of
hydrogen to 1-butene using a Ni catalyst.
22
Solution
Write the equation for the addition of
hydrogen to 1-butene using a Ni catalyst.
Ni
CH2=CH—CH2—CH3 + H2
CH3—CH2—CH2—CH3
23
Halogenation

In halogenation, halogen atoms add to the carbon
atoms of a double bond or triple bond.
Br Br
H2C CH2 +
Br2
H2C CH2
Cl Cl
HC C CH3 + 2Cl2
H C C CH3
Cl Cl
24
Testing for Double and Triple
Bonds


When bromine (Br2) is
added to an alkane, the
red color of bromine
persists.
When bromine (Br2) is
added to an alkene or
alkyne, the red color of
bromine disappears
immediately.
25
Learning Check
Write the product of each addition reaction:
CH2=CH—CH3 + H2
Pt
+ Br2
26
Solution
Write the product of each addition reaction:
CH2=CH—CH3 + H2
+ Br2
Pt
CH3—CH2—CH3
Br
Br
27
Hydrohalogenation

In hydrohalogenation, the atoms of a hydrogen
halide add to the carbon atoms of a double
bond or triple bond.
H
CH3 CH CH CH3 + HCl
+ HBr
Cl
CH3 CH CH CH3
H
Br
28
Markovnikov’s Rule

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.
H
Cl
CH3 CH CH2 Does not form
CH3 CH CH2 + HCl
C with the most H
Cl
H
CH3 CH CH2
Product that forms
29
Hydration Adds Water


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+.
+
H
CH3 CH CH2 + HOH
CH3 CH CH2
H+
+ HOH
OH H
H
OH
30
Learning Check
Write the products of each reaction.
A.
CH3 CH CH2 + Cl2
+
B.
C.
CH3 CH CH CH3 + HOH
+ H2
H
Pt
31
Solution
Write the products of each reaction.
Cl
A. CH3 CH CH2 + Cl2
CH3 CH CH2
H
+
B. CH3 CH CH CH3 + HOH
C.
+ H2
Cl
H
OH
CH3 CH CH CH3
Pt
H
H
32
13.8 Alkene Polymers
33
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.
34
Common Synthetic Polymers
35
Polymerization
In polymerization, small repeating units called
monomers are bonded to form a long chain
polymer.

H
H
+
C C
H
H
H
H
C C
H
H
+
H
H
C C
H
H
Ethylene monomers
chain continues
Repeating monomer
H H H
H H H
C C C
C C C
H H H
H H H
Polyethylene
chain continues
36
37
Recycling Plastics

1
2
3
4
5
6
Recycling is simplified by using
codes on plastic items.
PETE Polyethyleneterephtalate
HDPE High-density polyethylene
PV Polyvinyl chloride
LDPE Low-density
polyethylene
PP Polypropylene
PS Polystyrene
38
Learning Check

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 H
Polyvinyl chloride
39
Solution

What is the starting monomer for polyvinyl
chloride (PVC)?
H
Cl
+
C C
H
H
H
Cl
C C
H
H
+
H
Cl
C C
H
H
Chloroethene monomers
40
Chapter 13 Unsaturated
Hydrocarbons
13.6 Aromatic Compounds
41
13.9 Aromatic Compounds and the
Structure of Benzene





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.
42
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.
43
Aromatic Compounds in Nature
and Medicine
44
13.10 Naming Aromatic Compounds

A benzene with a single substituent is often named
as a benzene derivative.
CH3
Methylbenzene
Cl
Chlorobenzene
45
Some Common Names

Some substituted benzene rings have common
names that have been in use for many years.
CH3
Toluene
(Methylbenzene)
NH2
Aniline
(Benzenamine)
OH
Phenol
(Hydroxybenzene)
46
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-).
CH3
Br
Cl
Br
Cl
1,2-dimethylbenzene
(o-dibromobenzene)
1,3-dichlorobenzene
(m-dichlorobenzene)
Cl
4-chloromethylbenzene
(p-chlorotoluene)
47
Learning Check
Select the correct name for each structure:
Cl
1) chlorocyclohexane
2) chlorobenzene
3) 1-chlorobenzene
Cl
Cl
1) 1,3-dichlorobenzene
2) o-dichlorobenzene
3) m-dichlorobenzene
48
Solution
Select the correct name for each structure:
Cl
2) Chlorobenzene
Cl
1) 1,3-dichlorobenzene
3) m-dichlorobenzene
Cl
49
Learning Check
Write the structural formula for each:
A. 1-bromo-4-chlorobenzene
B. o-chlorotoluene
50
Solution
Write the structural formula for each:
Cl
A. 1-bromo-4-chlorobenzene
Br
CH3
B. o-chlorotoluene
Cl
51
Chapter 13 Unsaturated
Hydrocarbons
13.7 Properties of Aromatic Compounds
H
+
Benzene
Cl
Cl2
FeCl3
+
HCl
Chlorobenzene
52
13.11 Reactions 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.
53
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 (—NO2)

Sulfonation
—SO3H group
54
Halogenation


Halogenation replaces a H on benzene by a
chlorine or bromine atom.
A catalyst such as FeCl3 is used in chlorination;
FeBr3 in bromination.
H
+
Benzene
Cl
Cl2
FeCl3
+
HCl
Chlorobenzene
55
Nitration


Nitration replaces a H on benzene by a nitro
(—NO2) group from HNO3.
An acid catalyst such as H2SO4 is used in
nitration.
H
+ HNO3
Benzene
NO2
H2SO4
+
HOH
Nitrobenzene
56
Sulfonation


Sulfonation replaces a H on benzene by a
—SO3H group from SO3.
An acid catalyst such as H2SO4 is used in
sulfonation.
H
+ SO3
Benzene
SO3H
H2SO4
Benzenesulfonic acid
57
Learning Check
Write the equation for the bromination of
benzene, including catalyst.
58
Solution
Write the equation for the bromination of
benzene, including catalyst.
H
+ Br2
Br
FeBr3
+ HBr
59
Chapter Summary






Alkenes contain carbon-carbon double bonds.
Alkynes contain carbon-carbon triple bonds.
Aromatic compounds contain six carbons in a ring
arrangement with three double and three single
bonds alternating between carbon atoms.
Alkenes are named using the family ending –ene,
while the alkynes use the family ending –yne.
Alkenes and alkynes generally undergo addition
reactions and aromatic compounds generally
undergo substitution reactions.
Reaction mechanism: A description of the individual
steps by which old bonds are broken and new bonds
are formed.
60

End of Chapter 13
61
Thank you


Thanks so much for a wonderful semester.
You have been so wonderfully Kind to me.
I love you so much and will miss you.


Love
Divan
62