Unsaturated
hydrocarbons
Have fewer hydrogen atoms attached to the carbon chain than alkanes.
Are alkenes with double bonds.
Are alkynes with triple bonds.
1
Structure of Alkenes
Alkenes (and alkynes) are unsaturated hydrocarbons Alkenes have one or more double bonds
The two bonds in a double bond are different:
- one bond is a sigma () bond; these are cylindrical in shape and are very strong
- the other is a pi (π) bond; these involve sideways overlap of p-orbitals and are weaker than bonds
Alkenes are flat and have a trigonal planar shape around each of the two C’s in a double bond
Structure of Alkynes
Alkynes have one or more triple bonds
A triple bond consists of one bond and two π bonds - the two π bonds are orthogonal (perpendicular)
Alkynes are linear around each of the two C’s in the triple bond
Because alkenes and alkynes have π bonds, which are much weaker than bonds, they are far more chemically reactive than alkanes
Bond Angles in Alkenes and
Alkynes
According to VSEPR theory:
Three groups in a double bond are bonded at 120° angles.
Alkenes are flat: atoms in a C=C lie in the same plane.
The groups attached to a triple bond are at 180° angles.
6
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
cyclohexene
7
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.
8
Naming 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
propyne
9
Guide to Naming Alkenes and
Alkynes
10
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
2
3
1-butene
4
CH3─CH=CH─CH3
2-butene
11
Comparing Names of Alkanes,
Alkenes, and Alkynes
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
13
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
14
Solution
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─CC─CH3
2-butyne
2-methyl-2-butene
15
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
16
Cis and Trans Isomers
In an alkene, cis and trans isomers are possible because the double bond
Is rigid.
Cannot rotate.
Has groups attached to the carbons of the double bond that are fixed relative to each other.
CH3
CH = CH
cis
CH3
CH3
CH = CH
trans
CH3
17
Cis-Trans Isomers
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. 18
Cis-Trans Isomers
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.
19
Cis-Trans Isomerism
Cis-trans isomers do not occur if a carbon atom in the double bond is attached to identical groups.
Identical
HH
Identical
Br
H
Br
C C
HH
Br
H
C C
CH3
2-bromopropene
(not cis or trans)
H
Br
1,1-dibromoethene
(not cis or trans)
20
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
Br
Br
C C
H
H
Br
C C
H
cis-1,2-dibromoethene
H
Br
trans-1,2-dibromoethene
21
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.
22
Solution
Br
Br
C C
A.
cis-1,2-dibromoethene
H
H
H
CH3
trans-1,2-dimethylbutene
C C
B.
H
CH3
Cl
CH3
C.
C C
H
1,1-dichloro-2-methylpropene
Cl
Identical atoms on one C; no cis or trans
23
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. 24
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
Pt
H2C CH2
H2C CH2 + H2
H H
HC CH + 2H2
Ni
HC CH
H H
25
Hydrogenation of Oils
Adding H2 to double bonds in vegetable oils produces
Compounds with higher melting points.
Solids at room temperature such as margarine, soft margarine, and shortening.
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
26
Solution
Write an equation for the hydrogenation of 1-butene using a platinum catalyst.
Pt
CH2=CH─CH2─CH3 + H2
CH3─CH2─CH2─CH3
27
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.
28
Solution
Pt
CH3─CH=CH─CH3 + H2
+ H2
CH3─CH2─CH2─CH3
Pt
29
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
HC C CH3
Cl Cl
30
Solution
Write the product of the following addition reactions:
1. CH3─CH=CH─CH3 + Cl2
2.
Pt
Cl Cl l l
CH3─CH─CH─CH3
Br
+ Br2
Br
31
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
CH3
Cl
CH CH CH3
H
+ HBr
Br
32
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 .
H
Cl
CH3 CH CH2 Does not form
CH3
CH CH2 + HCl
Cl
CH3
C with the most H
H
CH CH2
Product that forms
33
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
34
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)
35
Solution
1.
2.
H OH
│ │
CH3─CH2─CH─CH─CH2─CH3
CH3
│
CH3─C─CH─CH2─CH3
│ │
OH H
OH
3.
H
36
Solution
Cl
A.
CH3 CH CH2 + Cl2
CH3
CH CH2
H
+
B. CH3 CH CH CH3 + HOH
C.
+ H2
H
Cl
OH
CH3 CH CH CH3
Pt
H
H
37
Polymers from Addition Reactions
38
More Monomers and Polymers
39
Solution
F F
│
│
F─C=C─F tetrafluoroethene
F
F F
F F F F
│
│
│
│
│
│
│
F
│
─C─C─C─C─C─C─C─C─
│
│
│
F
F F
│
│
│
│
F F F F
portion of Teflon
│
F
40
CH2=CHC6H5
CH2 =CHCl
CH2=CH2
CF2=CF2
CH2=CCl2
CH2=CHCO2CH2CH3
CH3CH=CH2
CH2=CHCN
CH3CH2Cl
CH2=CCO2CH3
styrofoam
PVC, construction tubing ethelyne Teflon, non stick coatings
1,1 dichloroethylene poly ethyl acrylate, latex paint
propylene orlon, acrylics and acrylates chloroethane polymethyl methacrylate, glass substitutes
41
Recycling Plastics
Recycling is simplified by using codes found on plastic items.
1
2
3
4
5
6
PETE Polyethyleneterephtalate
HDPE High-density polyethylene
PV Polyvinyl chloride
LDPE Low-density polyethylene
PP Polypropylene
PS Polystyrene
Copyright © 2007 by Pearson Education, Inc
. Publishing as Benjamin Cummings
42
Learning Check
What types of plastic are indicated by the following codes? 3
PV
A.
B.
C.
5
PP
6
PS
43
Solution
What types of plastic are indicated by the following codes? A.
B.
C.
.
3
PV
5
PP
6
PS
Polyvinyl chloride
Polypropylene
Polystyrene
44
Chapter 12 Unsaturated
Hydrocarbons
12.5
Aromatic Compounds
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
45
Benzene Structure
Benzene
Has 6 electrons shared equally among the 6 C atoms.
Is also represented as a hexagon with a circle drawn inside. 46
Aromatic Compounds in Nature and Health
O
Vanillin
Aspirin
CH
O
COH O
C O CH3
OCH3
O
OH
NH C CH3
Ibuprofen
CH3
H3C CH CH2
Acetaminophen
CH3 O
CH COH
OH
47
Naming Aromatic Compounds
Aromatic compounds are named
With benzene as the parent chain.
With one side group named in front of benzene.
CH3
methylbenzene
Cl
chlorobenzene
48
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.
CH3
toluene
(methylbenzene)
NH2
aniline
(benzenamine)
OH
phenol
(hydroxybenzene)
49
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 1,3para(p-) for 1,4-
50
Aromatic Compounds with Two
Groups
Cl
CH3
OH
Cl
Cl
Cl
3-chlorotoluene m-chlorotoluene 1,4-dichlorobenzene p-dichlorobenzene 2-chlorophenol o-chlorophenol 51
Learning Check
Select the correct name for each compound:
Cl
1) chlorocyclohexane
2) chlorobenzene
3) 1-chlorobenzene
1) 1,2-dimethylbenzene
2) m-xylene
3) 1,3-dimethylbenzene
CH 3
CH 3
52
Solution
Cl
2) chlorobenzene
CH 3
2) m-xylene
3) 1,3-dimethylbenzene
CH 3
53
Learning Check
Write the structural formulas for each of the following:
A. 1,3-dichlorobenzene
B. o-chlorotoluene
54
Solution
Cl
A. 1,3-dichlorobenzene
Cl
B. o-chlorotoluene
CH 3
Cl
55
Learning Check
Identify the organic family for each:
A. CH3─CH2─CH=CH2
B.
C. CH3─C≡CH
D.
56
Solution
Identify the organic family for each:
A. CH3─CH2─CH=CH2
alkene
B.
cycloalkane (alkane)
C. CH3─C≡CH
alkyne
D.
aromatic
57
Chapter 12 Unsaturated
Hydrocarbons
12.6
Properties of Aromatic
Compounds
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
58
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.
59
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
60
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.
H
+
Benzene
Cl
Cl2
FeCl3
+
HCl
Chlorobenzene
61
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.
H
+ HNO3
Benzene
NO2
H2SO4
+
HOH
Nitrobenzene
62
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.
H
+ SO3
Benzene
SO3H
H2SO4
Benzenesulfonic acid
63
Learning Check
Write the equation for the bromination of benzene including catalyst.
64
Solution
Write the equation for the bromination of benzene including catalyst.
H
+ Br2
Br
FeBr3
+ HBr
65