Ch. 11: Unsaturated
Hydrocarbons
Chem 20
El Camino College
1
Unsaturated Hydrocarbons
Unsaturated means that the molecule
contains one or more multiple bonds
 Alkenes contain a double bond
 Alkynes contain a triple bond

2
3

Label as alkane, alkene, or alkyne
H3C
alkene
C
C
alkyne
CH3
alkene
alkane
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Naming
Name the longest carbon chain that
contains the multiple bond (-ene or –yne)
 Number the chain to give the multiple bond
the lowest number, show location
 Give the location and name of each
substituent in alphabetical order, using
numbers, hyphens, and commas between
numbers
 Give location of the double bond (if needed)

5
Name These
H
C
H2C
CH3
H3C
C
H2
propene
C
C
CH3
2-butene
1-butene
2-butyne
6
Name These
Br
H
C
CH3
HC
C
H2C
C
C
H2
CH
Br
2-methylpropene
Br
Cl
4,4-dibromo-1-butyne
3-bromo-3-chloro-1-butene
7
Draw These
F
1-chloro-1,2,2-trifluoroethene
C
F
F
C
H
H
H
1,2-dimethyl-1-cyclohexene
Cl
CH3
H
C
C
H
CH3
H
H
H3C
1,1,4,4-tetrabromo-2-pentyne
Br
H
C
Br
Br
C
CH
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Br
Cis-Trans Isomers
cis--on the same side of the double bond
 trans--on opposite sides of the double bond

The cis and trans isomers are different
molecules and have different properties
 cis-2-butene bp = 3.7 oC
 trans-2-butene bp = 0.3 oC

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Cis-Trans Isomers
The groups that are cis and trans may differ
 cis & trans do not refer to gps on the same C
 The words cis and trans come first in the names,
followed by a hyphen

H
Br
H
H
F
H
F
Br
trans-1-bromo-2-fluoroethene
cis-1-bromo-2-fluoroethene
13
Write the names
1-pentene
4-chloro-1-pentene
Cl
trans-3-heptene
H
H
Br
cis-1-bromo-1-butene
14
Write the names
H3CH2C
CH2CH3
C
cis-3,4-dibromo-3-hexene
C
Br
Br
H3CH2C
Br
C
Br
trans-3,4-dibromo-3-hexene
C
CH2CH3
Br
trans-4,4,6,6-tetrabromo-2-hexene
Br
Br
Br
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Addition Reactions

In addition reactions of alkenes, the double
bond breaks and two atoms add to the
molecule
C

C
+
A
B
A
B
C
C
We’ll study some addition reactions
 Addition of H2 (hydrogenation)
 Addition of X2 (halogenation)
 Addition of H2O (hydration)
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Hydrogenation
In hydrogenation reactions of alkenes, the
double bond breaks & 2 H atoms add
 A catalyst such as Pt, Ni, or Pd speeds up
the reactions
 A cmpd with a multiple bond is unsaturated
 A cmpd with single bonds only is saturated

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Hydrogenation
Double bonds react with 1 molecule of H2
 Triple bonds react with 2 molecules of H2

C
C
C
C
+
+
H
2 H
H
H
Ni
Pd
H
H
C
C
H
H
C
C
H
H
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Write Product, Name
Reactant & Product
+
H
H
Pd
cyclopentene
cyclopentane
+
H
H
trans-4-methyl-2-pentene
Pt
2-methylpentane
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Halogenation
Double bond reacts with 1 molecule of bromine
Addition of bromine is useful for detection of carboncarbon double bond
20
Bromination
One cyclohexene molecule reacts with 1 molecule of
bromine to give 1,2-dibromo cyclohexane
Rapid decolorization of a bromine solution is
characteristic of compound containing carbon-carbon
double bond
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Hydration
In hydration reaction of alkene, the double
bond breaks, H and OH add with formation
of an alcohol
 An acid catalyst (shown as H+) is used
 If the two “C”s of the double bond are
attached to different groups, H adds to the
carbon of the double bond with more “H”s.

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Hydration
H
H
C
C
H
OH
H
H
H3C
H
C
H3C
H
H+
C
H
H
OH
H+
H3C
H
OH
C
C
H
H
H
OH
H
C
C
CH3
H
H
side with more "H"s
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Write Product, Name Reactant,
OH
+
H
OH
H+
C6H12O
cyclohexene
OH
+
H
OH
H+
C5H12O
2-methyl-2-butene
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3-D (Spatial) Drawings

Bonds lying on the plane of the paper are shown
with ordinary lines

Bonds coming out of the page are shown as solid
wedges
Bonds going to the back of the page are shown as
dashed (striped, broken)wedges

H
C
H
H
H
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3-D (Spatial) Drawings
H3C
CH2
CH2
H3C
is the same as
OH
H
O
is the same as
H
H
C
C
H

H
H
O
H
Note--every tetrahedral will have two lines,
one broken wedge(dash), and one solid
wedge. The lines make the zig-zag chain.
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3-D (Spatial) Drawings

Draw a spatial drawing for butane
H
H
H
C
H
H
C
C

H
C
H
H
H
H
Draw a spatial drawing for 2,2-dibromopropane
Br
Br
H
C
H
C
H
C
H
H
H
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3-D (Spatial) Drawings

Do not show planar atoms with dashes or wedges
H
H
H
H
H
H
C
C
H
C
C
H
H
ethene

ethyne
H
C
H
H
1-propene
Draw a spatial drawing for trans-1-bromo-1H
H
propene
H
C
H
C
Br
C
H
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Aromatic Hydrocarbon
Benzene molecule, C6 H6 , consists of a ring of six
carbon atoms with one hydrogen atom attached to
each carbon.
 Each carbon atom uses three valence electrons to
bond to hydrogen atom and two adjacent C atoms


Six electrons are shared equally among six
carbon atoms
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Naming of Aromatic
Hydrocarbon
When benzene has only one substituent the
benzene ring is not numbered.
 Example Chlorobenzene

When there are 2 or more substituents the
benzene ring is numbered to give the lower
numbers to the substituents.
 Example 1,3-dichlorobenzene

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Common name of Aromatic
Compounds
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Naming of Aromatic
Hydrocarbon

When a common name such as toluene, phenol
or aniline is used, the carbon atom attached to the
methyl, hydroxyl, or amine group is number as
carbon 1

Example: 2-chlorotoluene

Example: 4-ethyltoluene
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Polycyclic Aromatic
Compounds (PAHs)
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Polymer
Polymer are large molecules that consist of
small units called monomers
 Many are made by addition reaction of
alkenes. Examples:
 Polyethylene monomer is ethylene
 Polyvinyl chloride monomer is vinyl chloride

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