Chapter 11 Unsaturated
Hydrocarbons
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.
11.1
Alkenes and Alkynes
CH3—CH2—CH3
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Bond Angles in Alkenes and
Alkynes
Unsaturated Hydrocarbons
Unsaturated hydrocarbons
• have fewer hydrogen
atoms attached to the
carbon chain than alkanes.
• are alkenes with double
bonds.
• are alkynes with triple
bonds.
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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Copyright © 2009 by Pearson Education, Inc.
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Ethene (Ethylene)
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
Ethene, or ethylene,
• is an alkene with the formula
C2 H4 .
• 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.
cyclohexene
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Naming Alkynes
Naming Alkenes and 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
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
1-butene
4
CH3─CH=CH─CH3
1
propyne
2
3
2-butene
4
CH3─CH2─C≡C─CH3
5
4
3
2
2-pentyne
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Guide to Naming Alkenes and
Alkynes
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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
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Solution
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Learning Check
Write the IUPAC name for each of the following:
Write the IUPAC name for each of the following:
1. CH2=CH─CH2─CH3 1-butene
2. CH3─CH=CH─CH3
CH3
|
3. CH3─CH=C─CH3
2-butene
4. CH3─C≡C─CH3
2-butyne
A. CH3─CH2─C≡C─CH3
CH3
⎢
B. CH3─CH2─C=CH─CH3
2-methyl-2-butene
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Chapter 11 Unsaturated
Hydrocarbons
Solution
11.2
Cis-Trans Isomers
Write the IUPAC name for each of the following:
2-pentyne
A. CH3─CH2─C≡C─CH3
CH3
⎢
B. CH3─CH2─C=CH─CH3
3-methyl-2-pentene
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Copyright © 2009 by Pearson Education
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Cis and Trans Isomers
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Cis-Trans Isomers
In an alkene, the double bond
• is rigid.
• holds attached groups in fixed positions.
• makes cis-trans isomers possible.
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.
Copyright © 2009 by Pearson Education, Inc.
Copyright © 2009 by Pearson Education, Inc.
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Cis-Trans Isomers
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Cis-Trans Isomerism
• Alkenes cannot have cis-trans isomers if a carbon
atom in the double bond is attached to identical
groups.
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.
Identical
HH
Identical
Br
H
Br
HH
• In the trans isomer, the
groups and H atoms are
attached on opposite sides.
C C
CH3
2-Bromopropene
(not cis or trans)
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Br
H
C C
H
Br
1,1-Dibromoethene
(not cis or trans)
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Cis-Trans Isomers in Nature
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
• 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.
Br
Br
Br
H
H
C C
H
C C
H
cis-1,2-Dibromoethene
Br
trans-1,2-Dibromoethene
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Learning Check
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Solution
Name each, using cis-trans prefixes when needed.
H
C.
C C
H
CH3
Cl
CH3
Cl
CH3
C.
H
CH3
C C
H
Cl
trans-2-Butene
C C
B.
C C
B.
H
CH3
H
CH3
cis-1,2-Dibromoethene
H
H
H
H
C C
A.
C C
A.
Br
Br
Br
Br
1,1-Dichloropropene
Cl
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Chapter 11 Unsaturated
Hydrocarbons
22
Addition Reactions
11.3
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.
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Hydrogenation
Hydrogenation of Oils
Adding H2 to double
bonds in vegetable
oils produces
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.
• compounds with higher
melting points.
• solids at room
temperature, such as
margarine,
soft margarine,
and shortening.
H H
H2C CH2 + H2
Pt
H2C CH2
H H
HC CH + 2H2
Ni
HC CH
H H
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Learning Check
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Solution
Write an equation for the hydrogenation of 1-butene using
a platinum catalyst.
Pt
CH3─CH2─CH2─CH3
CH2=CH─CH2─CH3 + H2
Write an equation for the hydrogenation of 1-butene
using a platinum catalyst.
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Trans Fats
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Learning Check
(1) True or (2) False
In vegetable oils, the unsaturated fats usually contain
cis double bonds.
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.
• 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.
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Solution
Learning Check
Write the product of each the following:
(1) True or (2) False
Pt
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.
CH3─CH=CH─CH3 + H2
Pt
+ H2
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Solution
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
CH3─CH=CH─CH3 + H─OH
Pt
1. CH3─CH=CH─CH3 + H2
CH3─CH2─CH2─CH3
Pt
2.
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+ H2
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Hydration
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Learning Check
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
CH3─CH=CH2 + H─OH
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
H+
3.
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+ HOH
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Chapter 11 Unsaturated
Hydrocarbons
Solution
1.
2.
11.4
Polymers of Alkenes
H OH
│
│
CH3─CH2─CH─CH─CH2─CH3
CH3
│
CH3─C─CH─CH2─CH3
│ │
OH H
OH
3.
H
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Polymers
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Common Synthetic Polymers
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.
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Common Synthetic Polymers
40
Common Synthetic Polymers
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Copyright © 2009 Pearson Education, Inc.
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Polymerization
Polymers from Addition Reactions
In polymerization, small repeating units called monomers
join to form a long chain polymer.
H
H
H
H
+
C C
H
H
C C
H
H
+
H
H
monomer unit repeats
C C
H
H
Ethylene monomers
H H H
chain continues
H H H
C C C
C C C
H H H
H H H
chain continues
n
Polyethylene
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Learning Check
More Monomers and Polymers
What is the starting monomer for polyethylene?
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Solution
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Learning Check
Name the monomer used to make Teflon, and write a
portion of a Teflon polymer using four monomers.
Ethene (ethylene)
CH2=CH2
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Solution
Recycling Plastics
F F
│
Recycling is simplified by using codes on plastic items.
│
F─C=C─F
F
F F
tetrafluoroethene
1
2
3
4
5
6
7
F F F F F
│
│
│
│
│
│
│ │
│
│
│
│
│
│
│ │
F
F F
─C─C─C─C─C─C─C─C─
portion of Teflon
F F F F F
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
Solution
What types of plastic are indicated by the following
codes?
A.
B.
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What types of plastic are indicated by the following
codes?
3
PV
A.
B.
5
PP
3
PV
5
PP
C.
C.
6
PS
.
Polyvinyl chloride
Polypropylene
Polystyrene
6
PS
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Chapter 11 Unsaturated
Hydrocarbons
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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.
11.5
Aromatic Compounds
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Copyright © 2009 Pearson Education, Inc.
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Aromatic Compounds in Nature and
Health
Benzene Structure
Benzene
• has 6 electrons shared equally among the 6 C atoms.
• is also represented as a hexagon with a circle drawn
inside.
O
Vanillin
Aspirin
CH
O
COH O
C O CH3
OCH3
O
OH
Ibuprofen
Acetaminophen
NH C CH3
CH3 O
CH3
H3C CH CH2
CH COH
OH
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Naming Aromatic Compounds
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.
Aromatic compounds are named
• with benzene as the parent chain.
• with one side group named in front of benzene.
CH3
Cl
Methylbenzene
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OH
NH2
CH3
Chlorobenzene
Toluene
(methylbenzene)
Aniline
(benzenamine)
Phenol
(hydroxybenzene)
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Naming Aromatic Compounds
Learning Check
Select the correct name for each compound.
Cl
1) chlorocyclohexane
2) chlorobenzene
3) 1-chlorobenzene
When two groups are attached to the benzene ring, the
ring is numbered to give the lowest numbers to the side
groups.
Cl
CH3
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OH
Cl
1) 1,2-dimethylbenzene
2) 1,4-dimethylbenzene
3) 1,3-dimethylbenzene
CH 3
Cl
3-Chlorotoluene
Cl
1,4-Dichlorobenzene
CH3
2-Chlorophenol
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Solution
Learning Check
Select the correct name for each compound.
Write the structural formulas for each of the following:
A. 1,3-dichlorobenzene
Cl
2) chlorobenzene
B. 2-chlorotoluene
CH 3
3) 1,3-dimethylbenzene
CH 3
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Solution
Learning Check
Identify the organic family for each:
Write the structural formulas for each of the following:
A. 1,3-dichlorobenzene
Cl
A. CH3─CH2─CH=CH2
B.
Cl
B. 2-chlorotoluene
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C. CH3─C≡CH
CH3
Cl
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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