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1
Chapter 11 Unsaturated Hydrocarbons
11.1
Alkenes and Alkynes
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
2
Unsaturated hydrocarbons Have fewer hydrogen
atoms attached to the carbon chain than alkanes.
Are alkenes with double bonds.
Are alkynes with triple bonds.
Unsaturated Hydrocarbons
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
3
Bond Angles in Alkenes and Alkynes
According to VSEPR theory: Three groups in a double
bond are bonded at 120° angles.
Alkenes are flat, because the atoms in a double bond lie in the same plane.
The groups attached to a triple bond are at 180° angles.
Physical properties
Similar to alkanes SolubilitySolubility
• Soluble in nonpolar solvents
• Not soluble in water
Low density, boiling point and melting point
Properties vary based on chain size
Interesting physical property. Alkenes with several double bonds will have a
color associated with them.
Colored alkenes
lycopene - red of tomato, paprika and watermelonlycopene - red of tomato, paprika and watermelon
-carotene, yellow of carrots and yams-carotene, yellow of carrots and yams
CH3
H3C CH3CH3 CH3
CH3CH3
H3C
CH3H3C
CH3
H3C CH3CH3 CH3
CH3CH3
H3C
CH3H3C
6
Naming Alkenes
The names of alkenes Use the corresponding alkane name. Change the ending to ene.
Alkene IUPACCommon
H2C=CH2 ethene ethylene
H2C=CH─CH3 propene propylene
cyclohexene
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Ethene (ethylene)
Ethene or ethylene Is an alkene 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 © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
8
Naming Alkynes
The names of alkynes Use the corresponding alkane name. Change the ending to yne.
Alkyne IUPACCommon
HC≡CH ethyne acetylene
HC≡C─CH3 propyne
9
Guide to Naming Alkenes and Alkynes
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
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Naming Alkenes
Write the IUPAC name for CH2=CH─CH2─CH3 and
CH3─CH=CH─CH3
STEP 1 Name the longest carbon chain
butene
STEP 2 Number the chain from the double bond
CH2=CH─CH2─CH3 1-butene
1 2 3 4
CH3─CH=CH─CH3 2-butene
11
Comparing Names of Alkanes, Alkenes, and Alkynes
TABLE 12.1
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12
Naming Alkenes with Substituents
CH3
│
Write the IUPAC name for CH3─CH─CH=CH─CH3
STEP 1 Name the longest carbon chain pentene
STEP 2 Number the chain from the double bond
CH3
│
CH3─CH─CH=CH─CH3 2-pentene 5 4 3 2 1
STEP 3 Give the location of each substituent 4-methyl- 2-pentene
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Naming Alkynes with Substituents
CH3
│
Write the IUPAC name for HC≡C─CH─CH3
1 2 3 4
STEP 1 Name the longest carbon chain butyne
STEP 2 Number the chain from the double bond
1-butyne
STEP 3 Give the location of each substituent
3-methyl-1-butyne
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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─CC─CH3
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Solution
Write the IUPAC name for each of the following:
1. CH2=CH─CH2─CH3 1-butene
2. CH3─CH=CH─CH3 2-butene
CH3
|3. CH3─CH=C─CH3 2-methyl-2-butene
4. CH3─CC─CH3 2-butyne
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Learning Check
Write the structural formula for each of the following:
A. 2-pentyne
B. 3-methyl-2-pentene
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Solution
Write the structural formula for each of the following:
A. CH3─CH2─C≡C─CH3 2-pentyne
CH3
B. CH3─CH2─C=CH─CH3 3-methyl-2-pentene
18
Chapter 12 Unsaturated Hydrocarbons
12.2
Cis-Trans Isomers
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
19
Cis-trans isomers occur when different groups are attached to the double bond.
In a cis isomer, groups on the same side of C=C
In the trans isomer, the groups on opposite sides.
Cis-Trans Isomers
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Cis-trans isomers
Can be modeled by making a “double bond” with your fingers with both thumbs on the same side or opposite from each other.
Cis-Trans Isomers
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
21
Cis-trans isomers occur when
different 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.
Cis-Trans Isomers
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22
Cis-Trans Isomerism
Cis-trans isomers do not occur if a carbon atom in the double bond is attached to identical groups.
Identical Identical
2-bromopropene 1,1-dibromoethene (not cis or trans) (not cis or trans)
C C
H Br
H CH3
C C
H Br
BrH
H
H
H Br
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Naming Cis-Trans Isomers
The prefixes cis or trans are placed in front of the alkene name when there are cis-trans isomers.
cis trans
cis-1,2-dibromoethene trans-1,2-dibromoethene
C C
Br H
BrH
C C
Br Br
H H
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Pheromones
A pheromone
Is a chemical messenger emitted by insects in tiny quantities.
Called bombykol emitted by the silkworm moth to attract other moths has one cis and one trans double bond.
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
25
Learning Check
Name each, using cis-trans prefixes when needed.
C C
CH3 H
CH3H
C C
Br Br
H H
A.
B.
C C
CH3 Cl
ClH
C.
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Solution
cis-1,2-dibromoethene
trans-2-butene
1,1-dichloropropene
C C
CH3 H
CH3H
C C
Br Br
H H
A.
B.
C C
CH3 Cl
ClH
C.
Identical atoms on one C; no cis or trans
27
Chapter 12 Unsaturated Hydrocarbons
12.3
Addition Reactions
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
28
Addition Reactions
In addition reactions, Reactants add to the
carbon atoms in double or triple bonds.
A double or triple bond is easily broken, which makes them very reactive.
TABLE 12.2
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
29
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.
Hydrogenation
HC CH + 2H2Ni
HC CH
H H
H H
H2C CH2
H HPt
H2H2C CH2 +
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Adding H2 to double
bonds in vegetableoils produces Compounds with
higher melting points. Solids at room
temperature such as margarine,
soft margarine,
and shortening.
Hydrogenation of Oils
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
32
Solution
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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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.
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Learning Check
(T) True or (F) False
A. ____ There are more unsaturated fats in vegetable oils.
B. ____ Hydrogenation converts some cis-double bonds to
trans- double bonds.
C. ____ Animal fats have more unsaturated fats.
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Solution
(1) True or (2) False
A. T There are more unsaturated fats in vegetable oils.
B. T Hydrogenation of oils converts some cis-double
bonds to trans- double bonds.
C. F Animal fats have more unsaturated fats.
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Halogenation
In halogenation, halogen atoms add to the carbon atoms of a double bond or triple bond.
+ CH3CHC 2Cl2CH3
ClCl
ClCl
CHC
BrBr
CH2H2C Br2CH2 +H2C
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Write the product of the following addition reactions: 1. CH3─CH=CH─CH3 + Cl2
2. + Br2
Learning Check
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Solution
Write the product of the following addition reactions:
Pt1. CH3─CH=CH─CH3 + Cl2
Cl Cl l l
CH3─CH─CH─CH3
2.
Br
Br + Br2
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Testing for Unsaturation
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.
Br2
Br2
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
15
42
Hydrohalogenation
In hydrohalogenation, the atoms of a hydrogen halide add to the carbon atoms of a double bond or triple bond.
ClH
CH3 CHCHCH3+ HClCH3CHCHCH3
Br
H + HBr
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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 atoms .
HCl
CH2CHCH3
CH2CHCH3 + HCl
ClH
CH2CHCH3 Does not form
C with the most H
Product that forms
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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
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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 most H. The OH bonds to the C in the double bond with the
fewest H atoms.
OH H H+ │ │CH3─CH=CH2 + H─OH CH3─CH─CH2
(1H) (2H)
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Learning Check
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. + HOH
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Learning Check
Write the products of each reaction.
C.
B.
A.
HOH +CH3CHCHCH3
Pt
+ Cl2 CH2CHCH3
+ H2
H+
50
Chapter 12 Unsaturated Hydrocarbons
12.4
Polymers of Alkenes
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
51
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, Teflon, and nylon. Made up of small repeating units called
monomers. Made by reaction of small alkenes.
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Polymerization
In polymerization, small repeating units called monomers join to form a long chain polymer.
monomer unit repeats
n
53
Common Synthetic Polymers
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
54
Polymers from Addition Reactions
TABLE 12.3
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
55
More Monomers and Polymers
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
58
Learning Check
Name the monomer used to make Teflon and write a
portion of a Teflon polymer using four monomers.
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Solution
F F │ │
F─C=C─F tetrafluoroethene
F F F F F F F F │ │ │ │ │ │ │ │
─C─C─C─C─C─C─C─C─ portion of Teflon │ │ │ │ │ │ │ │
F F F F F F F F
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Recycling Plastics
Recycling is simplified by using codes found
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 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
62
Solution
What types of plastic are indicated by the followingcodes?
A. Polyvinyl chloride
B. Polypropylene
C. Polystyrene
.
3PV
5PP
6PS
63
Chapter 12 Unsaturated Hydrocarbons
12.5
Aromatic Compounds
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
64
Benzene Has 6 electrons shared equally among the 6 C atoms.
Is also represented as a hexagon with a circle drawn inside.
Benzene Structure
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
65
Aromatic Compounds in Nature and Health
Vanillin Aspirin
Ibuprofen Acetaminophen
COH
O
O
C O CH3
CH
O
OCH3
OH
CH
CH3
COH
O
CH2
CH3
CHH3COH
NH
O
C CH3
66
Naming Aromatic Compounds
Aromatic compounds are named
With benzene as the parent chain.
With one side group named in front of benzene.
methylbenzene chlorobenzene
ClCH3
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Some Common Names
Some substituted benzene rings
Have common names used for many years.
With a single substituent use a common name or are named as a benzene derivative.
toluene aniline phenol
(methylbenzene) (benzenamine) (hydroxybenzene)
NH2 OHCH3
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Aromatic Compounds with Two Groups
Two naming systems are used when two groups are
attached to a benzene ring.
Number the ring to give the lowest numbers to the side groups.
Use prefixes to show the arrangement:
ortho(o-) for 1,2-
meta(m-) for 1,3-
para(p-) for 1,4-
69
Aromatic Compounds with Two Groups
3-chlorotoluene 1,4-dichlorobenzene 2-chlorophenol
m-chlorotoluene p-dichlorobenzene o-chlorophenol
OHCH3
Cl
Cl
Cl
Cl
70
Learning Check
Select the correct name for each compound:1) chlorocyclohexane2) chlorobenzene3) 1-chlorobenzene
1) 1,2-dimethylbenzene2) m-xylene3) 1,3-dimethylbenzene
CH3
CH3
Cl
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Learning Check
Write the structural formulas for each of the following:
A. 1,3-dichlorobenzene
B. o-chlorotoluene
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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
76
Chapter 12 Unsaturated Hydrocarbons
12.6 Properties of Aromatic
Compounds
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77
Properties of Aromatic Compounds
Aromatic compounds Have a stable aromatic bonding system. Are resistant to many reactions. Undergo substitution reactions, which retain
the stability of the aromatic bonding system.
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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
79
Halogenation
In a halogenation An H atom of benzene is replaced by a chlorine or
bromine atom. A catalyst such as FeCl3 is needed in chlorination.
A catalyst such as FeBr3 is needed in bromination.
ChlorobenzeneBenzene
FeCl3 HCl+
Cl
Cl2+
H
80
Nitration
In the nitration of benzene An H atom of benzene is replaced by a nitro (-NO2)
group from HNO3.
An acid catalyst such as H2SO4 is needed.
NitrobenzeneBenzene
H2SO4 HOH+
NO2
HNO3+
H
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Sulfonation
In a sulfonation An H atom on benzene is replaced by a —SO3H
group from SO3.
An acid catalyst such as H2SO4 is needed.
Benzenesulfonic acidBenzene
H2SO4
SO3H
SO3+
H