ORGANIC CHEMISTRY
CHM 207
CHAPTER 3:
ALKENES
NOR AKMALAZURA JANI
SUBTOPICS
• Naming alkenes and cycloalkenes.
• Physical properties of alkenes:
i) boiling points and densities
ii)polarity
• Preparation of alkenes:
i) dehydration of alcohols
ii) dehydrohalogenation of haloalkanes
• Reactions of alkenes:
i) Addition reaction:
a) Catalytic hydrogenation
b) Addition of halogens
- In inert solvent
- In water / aqueous medium
c) Addition of hydrogen halides
d) Addition reaction with concentrated sulfuric acid: hydration of
alkenes
e) Addition reaction with acidified water (H3O+): hydration of alkenes
ii) Combustion of alkenes
iii) Oxidation:
a) epoxidation
b)hydroxylation
c)Ozonolysis
iv) Polymerization
• Unsaturation tests of alkenes:
i) Reactions of alkenes with KMnO4
ii) Reactions of alkenes with bromine.
• Uses of alkenes:
i) PE
ii) PVC
iii) ethanol
ALKENES
• Also called olefins
• Contain at least one carbon-carbon double bond
(C=C)
• General formula, CnH2n (n=2,3,…)
• Classified as unsaturated hydrocarbons
(compound with double or triple carbon-carbon
bonds that enable them to add hydrogen atoms.
• sp2-hybridized
• For example:
C2H4 - ethylene
CH2
CH2
Naming Alkenes
IUPAC RULES
RULE 1. Select the longest continuous
carbon chain that contains a double bond.
This chain
contains 6
carbon atoms
RULE 2. Name this compound as you would an
alkane, but change –ane to –ene for an alkene.
This chain
contains 8
carbon atoms
Nameisthe
This
theparent
longest
continuous octene.
compound
chain.
Select it as the parent
compound.
RULE 3. Number the carbon chain of the
parent compound starting with the end nearer to
the double bond. Use the smaller of the two
numbers on the double-bonded carbon to
indicate the position of the double bond. Place
this number in front of the alkene name.
IUPAC RULES
This end of the chain is closest to the
double bond. Begin numbering here.
IUPAC RULES
The name of the parent compound is
1-octene.
4
3
2
1
5
6
7
8
RULE 4. Branched chains and other groups are
treated as in naming alkanes. Name the
substituent group, and designate its position on
the parent chain with a number.
IUPAC RULES
The
is attached to carbon 4.
Thisethyl
is an group
ethyl group.
4
3
2
1
5
6
7
8
4-ethyl-1-octene
NEW IUPAC NAMES
• Placing numbers (location of double bond) before the
part of the name –ene.
• Example:
1
2
3
4
CH2 C CH2
H
CH3
Old naming system: 1-butene
New naming system: but-1-ene
1
2
CH2 C
H
1
CH3 C
H
3
4
5
6
C CH2 CH2 CH3
H
Old naming system: 2-hexene
New naming system: hex-2-ene
CH3
3
2
4
C CH3
H
Old naming system: 3-methyl-1-butene
New naming system: 3-methylbut-1-ene
• A compound with more than one double bond.
- Two double bond: diene
- Three double bond: triene
- Four double bond: tetraene
* Numbers are used to specify the locations of the double bonds.
1
2
3
CH2 C
H
4
C CH2
H
7
6
CH3 C C
H H
IUPAC names: 1,3-butadiene
new IUPAC names: buta-1,3-diene
1
2
8
3
7
4
6
5
5
IUPAC names: 1,3, 5, 7-cyclooctatetraene
new IUPAC names: cycloocta-1,3,5,7-tetraene
4
3
C
H
C
H
2
C
H
1,3,5-heptatriene
hepta-1,3,5-triene
1
CH2
ALKENES AS SUBSTITUENTS
• Alkenes names as substituents are called alkenyl groups.
• Can be named systematically as ethenyl, propenyl, etc. or
by common names such as vinyl, ally, methylene and
phenyl groups.
CH2
methylene group
(methylidene group)
-CH=CH2
vinyl group
(ethenyl group)
-CH2-CH=CH2
allyl group
(2-propenyl group)
CH=CH2
CH2 CHCHCH2CH CH2
3-methylenecyclohexene
IUPAC name: 3-vinyl-1,5-hexadiene
New IUPAC name: 3-vinylhexa-1,5-diene
CYCLOALKENES
• Contains C=C in the ring
cyclopropene
cyclohexene
cyclobutene cyclopentene
• Nomenclature of cycloalkenes:
- Similar to that alkenes
- Number the cycloalkane so that the double bond is between C1 and
C2 and so that the first substituent has as low a number as possible.
* Double bond always between C1 and C2.
6
5
4
1
2
1
CH3
3
1-methylcyclohexene
5
4
6
2
CH2CH3
1
3
2
1,5-dimethylcyclopentene
5
3
4
IUPAC name: 2-ethyl-1,3-cyclohexadiene
New IUPAC name: 2-ethylcyclohexa-1,3-diene
NOMENCLATURE OF cis-trans ISOMERS
H3C
H
C
C
CH2CH3
H
cis-2-pentene
H3C
H
H
C
C
CH2CH3
trans-2-pentene
• cis – two particular atoms (or groups of atoms) are
adjacent to each other
• trans – the two atoms (or groups of atoms) are
across from each other
PHYSICAL PROPERTIES OF ALKENES
Boiling points and densities:
- Most physical properties of alkenes are similar to
those alkanes.
- Example: the boiling points of 1-butene, cis-2-butene,
trans-2-butene and n-butane are close to 0oC.
- Densities of alkenes: around 0.6 or 0.7 g/cm3.
- Boiling points of alkenes increase smoothly with
molecular weight.
- Increased branching leads to greater volatility and
lower boiling points.
Polarity:
- relatively nonpolar.
- insoluble in water but soluble in non-polar
solvents such as hexane, gasoline, halogenated
solvents and ethers.
- slightly more polar than alkanes because:
i) electrons in the pi bond is more polarizable
(contributing to instantaneous dipole
moments).
ii) the vinylic bonds tend to be slightly polar
(contributing to a permanent dipole moment).


Alkyl groups are electron donating toward double
bond, helping to stabilize it. This donating slightly
polarizes the vinylic bond, with small partial positive
charge on the alkyl group and a small negative charge
on the double bond carbon atom.
For example, propene has a small dipole moment of
0.35 D.
Vinylic bonds
H3C
H
C
H
H3C
C
CH3
C
H
propene, μ = 0.35 D
H
H3C
C
H
C
H
H
C
CH3
Vector sum =
Vector sum = 0
propene, μ = 0.33 D propene, μ = 0
cis-2-butene, bp 4oC trans-2-butene, bp 1oC
C
• In a cis-disubstituted alkene, the vector sum of the two
dipole moments is directed perpendicular to the
double bond.
• In a trans-disubstituted alkene, the two dipole
moments tend to cancel out. If an alkene is
symmetrically trans-disubstituted, the dipole moment
is zero.
H
H3C
C
CH3
C
H
H
H3C
C
H
C
H
H
C
CH3
Vector sum =
Vector sum = 0
propene, μ = 0.33 D propene, μ = 0
cis-2-butene, bp 4oC trans-2-butene, bp 1oC
C
• Cis- and trans-2-butene have similar van der Waals
attractions, but only cis isomer has dipole-dipole
attractions.
• Because of its increased intermolecular attractions,
cis-2-butene must be heated to a slightly higher
temperature (4oC versus 1oC) before it begins to boil.
H
H3C
C
CH3
C
H
H
H3C
C
H
C
H
H
C
CH3
Vector sum =
Vector sum = 0
propene, μ = 0.33 D propene, μ = 0
cis-2-butene, bp 4oC trans-2-butene, bp 1oC
PREPARATION OF ALKENES
 Dehydration of alcohols
 Dehydrohalogenation of haloalkanes
PREPARATION OF ALKENES
• Alkenes can be prepared in the following ways:
i) Dehydration of alcohols
R-CH2-CH2-OH
conc. H2SO4
R-CH=CH2 + H2O
ii) Dehydrohalogenation of haloalkanes
R-CH2-CH2-X
NaOH/ethanol
reflux
NaOH can be replaced by KOH
R-CH=CH2 + HX
• Saytzeff rule:
- A reaction that produces an alkene would favour the
formation of an alkene that has the greatest number of
substituents attached to the C=C group.
Dehydration of alcohols
CH3CH2-CH-CH3
OH
H+
CH3CH2-CH=CH2 + H2O
1-butene
+
H
CH3CH=CH-CH3 + H2O
2-butanol
2-butene
major product
Dehydrohalogenation of haloalkanes
CH3CH-CH-CH2
H
Br H
2-bromobutane
KOH
alcohol
reflux
CH3CH=CH-CH3
2-butene
(major product)
CH3CH2CH=CH2
1-butene
REACTIVITY OF ALKENES
More reactive than alkanes because:
i)
A carbon-carbon double bond consists of a σ and a π
bond. It is easy to break the π bond while the σ bond
remains intact.
ii)
The π electrons in the double bond act as a source of
electrons (Lewis base). Alkenes are reactive towards
electrophiles which are attracted to the negative charge
of the π electrons.
iii)
π bond will broken, each carbon atom becomes an
active site which can form a new covalent bond with
another atom. One π bond is converted into 2 σ bonds.
REACTION OF ALKENES
i) Addition reaction:
a) Catalytic hydrogenation
b) Addition of halogens
- In inert solvent
- In water / aqueous medium
c) Addition of hydrogen halides
d) Addition reaction with concentrated sulfuric acid: hydration of
alkenes
e) Addition reaction with acidified water (H3O+): hydration of alkenes
ii) Combustion of alkenes
iii) Oxidation:
a) epoxidation
b)hydroxylation
c)Ozonolysis
iv) Polymerization
REACTIONS OF ALKENES
Catalytic hydrogenation:
- hydrogenation: addition of hydrogen to a double bond and
triple bond to yield saturated product.
- alkenes will combine with hydrogen in the present to
catalyst to form alkanes.
C C
H H
Pt or Pd
o
25-90 C
C C
H H
- Plantinum (Pt) and palladium (Pd) – Catalysts
- Pt and Pd: temperature 25-90oC
- Nickel can also used as a catalyst, but a higher temperature
of 140oC – 200oC is needed.
EXAMPLES:
H2C CH2
ethylene
CH3CH2CH2CH2CH CH2
hexene
H2
H2
Pt
low pressure
Pt
low pressure
H3C CH3
ethane
CH3CH2CH2CH2CH2CH3
hexane
Addition of halogens:
i) In inert solvent:
- alkenes react with halogens at room temperature and in dark.
- the halogens is usually dissolved in an inert solvent such as
dichloromethane (CH2Cl2) and tetrachloromethane (CCl4).
- Iodine will not react with alkenes because it is less reactive
than chlorine and bromine.
inert solvent
C C
X
C CThe reaction will produced
- Fluorine
isX very reactive.
X X
explosion.
X X = halogen such as Br or Cl
2
Inert solvent = CCl4 or CH2Cl2
2
EXAMPLES:
H H
H C C H
H H
H C C H
Br Br
inert solvent (CCl4)
Br Br
ethene
1,2-dibromoethane
* the red-brown colour of the bromine solution will fade and the
solution becomes colourless.
Br2
CCl4
Br
1,2-dibromocyclohexane
cyclohexene
CH3CH=CH2
propene
Br
Cl2
CCl4
Cl Cl
CH3CH CH2
1,2-dichloropropane
Addition of halogens:
ii) In water / aqueous medium:
- chlorine dissolves in water to form HCl and chloric (l) acid
(HOCl).
Cl2 (aq) + H2O(l)
HCl(aq) + HOCl (aq)
- same as bromine
Br2 (aq) + H2O(l)
HBr(aq) + HOBr(aq)
* Reaction of alkenes with halogens in water (eg. chlorine
water and bromine water) produced halohydrins (an
alcohol with a halogen on the adjacent carbon atom).
EXAMPLES:
CH3CH=CH2
+
Br2
H 2O
propene
CH3 CH CH2
CH3 CH CH2
Br Br
OH Br
1-bromo-2-propanol 1,2-dibromopropane
(major product)
(minor product)
* Br atom attached to the carbon atom of the double bond which has the greater
number of hydrogen atoms.
CH3CH2CH=CH2
1-butene
Cl2, H2O
CH3 CH2 CH CH2
OH Cl
1-chloro-2-butanol
Addition of hydrogen halides:
- Addition reaction with electrophilic reagents.
- Alkenes react with hydrogen halides (in gaseous state or
in aqueous solution) to form addition products.
- The hydrogen and halogen atoms add across the double
bond to form haloalkanes (alkyl halides).
- General equation:
C C
alkene
HX
H X
C C
haloalkane
- Reactivity of hydrogen halides : HF < HCl < HBr < HI
* Reaction with HCl needs a catalyst such as AlCl3
H2C CH2
HCl
AlCl3
CH3CH2Cl
EXAMPLES:
H-I
cyclopentene
CH3CH=CHCH3 + H-Br
2-butene
I
iodocyclopentane
Br
CH3CH2CHCH3
2-bromobutane
MARKOVNIKOV’S RULE
• There are 2 possible products when hydrogen halides react
with an unsymmetrical alkene.
• It is because hydrogen halide molecule can add to the C=C
bond in two different ways.
H H
CH3 C C H
H H
H-I
CH3 C C H
H I
1-iodopropane
H H
CH3 C C H
H H
H-I
CH3 C C H
I H
2-iodopropane
(major product)
Markovnikov’s rules:
- the addition of HX to an unsymmetrical
alkene, the hydrogen atom attaches itself
to the carbon atom (of the double bond)
with the larger number of hydrogen atoms.
Mechanism of electrophilic addition reactions:
- C=C : electron rich part of the alkene molecule
- Electrophiles: electron-seeking
Step 1: Formation of carbocation.
Attack of the pi bond on the electrophile to form carbocation.
δ+
C C
E
δ-
C C
Y
Y-
E
carbocation
Step 2: Rapid reaction with a negative ion.
The negative ion (Y-) acts as nucleophile and attacks the
positively charged carbon atom to give product of the
addition reaction.
C C
E
Y-
C C
E Y
ADDITION OF HYDROGEN HALIDES TO
UNSYMMETRICAL ALKENES AND
MARKOVNIKOV’S RULE
CH3CHCH2
1
2
3
CH3CH=CH2
HCl
H Cl
1-chloropropane
Propene
CH3CHCH2
Cl H
2-chloropropane
(major product)
according to Markovnikov's
rules
MECHANISM:
Step 1: Formation of carbocation
H H H
H H
CH3 C C H
H C C C H or H C C C H
H
H
H H
H Cl
less stable carbocation
o
(1 carbocation)
o
H H H
Cl-
more stable carbocation
(2o carbocation)
o
- 2 carbocation is more stable than 1 carbocation.
- 2o carbocation tends to persist longer, making it more likely to combine with
Cl- ion to form 2-chloromethane (basis of Markovnikov's rule).
Step 2: Rapid reaction with a negative ion
H H H
H C C C H
H
H
H H H
Cl-
H C C C H
H Cl H
2-chloromethane (major product)
Addition reaction with concentrated sulfuric
acid: hydration of alkenes
- the alkene is absorbed slowly when it passed
through concentrated sulfuric acid in the cold
(0-15oC).
- involves the addition of H atom and HSO4
group across the carbon-carbon double bond.
- follows Markovnikov’s rule.
H H
H C C H
H H
H OSO3H
(H2SO4)
H C C H
H OSO3H
ethyl hydrogensulphate
(CH3CH2HSO4)
When the reaction mixture is added to water and warmed,
ethyl hydrogensulphate is readily hydrolysed to ethanol
CH3CH2OSO3H + H-OH
CH3CH2OH + H2SO4
(H2O)
*ethene reacts with concentrated H2SO4 to form ethanol*
or
*alkene reacts with concentrated H2SO4 to form alcohol*
Addition reaction with acidified water (H3O+): hydration of
alkenes
• Hydration: The addition of H atoms and –OH groups from
water molecules to a multiple bond.
• Reverse of the dehydration reaction.
• Direct hydration of ethene:
- passing a mixture of ethene and steam over phosphoric (v)
acid (H3PO4) absorbed on silica pellets at 300oC and a
pressure of 60 atmospheres.
- H3PO4 is a catalyst.
CH2=CH2 (g)
H2O (g)
ethene
C C
alkene
H3PO4
o
300 C, 60 atm
H2O
H+
CH3CH2OH (g)
H OH
C C
alcohol
ethanol
• Markovnikov’s rule is apply to the addition of a water
molecule across the double bond of an unsymmetrical
alkene.
• For examples:
CH3
CH3 C
CH2
CH3
+
H
25oC
H OH
CH3 C
2-methylpropene
CH2
OH H
tert-butyl alcohol
CH3CH=CH2 + H2O
propene
H+
CH3CHCH3
OH
2-propanol
H+ = catalyst
MECHANISM OF ACID CATALYSED HYDRATION OF ALKENES
Step 1: Protonation to form carbocation
H H
CH3 C C H
H H H
+
H
H C C C H
H
H
more stable carbocation
(2o carbocation)
Step 2: Addition of H2O to form a protonated alcohol
H H H
H C C C H
H
H
CH3CHCH3
H
O
O H
H
H
Step 3: Loss of a proton (deprotonated) to form alcohol
CH3CHCH3
O H
H
CH3CHCH3
OH
H+
H+ = catalyst
ANTI-MARKOVNIKOV’S RULE: FREE RADICAL
ADDITION OF HYDROGEN BROMIDE
• When HBr is added to an alkene in the absence of peroxides
it obey Markovnikov’s rule.
• When HBr (not HCl or HI) reacts with unsymmetrical alkene
in the presence of peroxides (compounds containing the OO group) or oxygen, HBr adds in the opposite direction to
that predicted by Markovnikov’s rule.
• The product between propene and HBr under these
conditions is 1-bromopropane and not 2-bromopropane.
CH3CH=CH2
HBr
peroxide
CH3CH2CH2Br
1-bromopropane
(major product)
anti-Markovnikov's orientation
• Anti-Markovnikov’s addition:
- peroxide-catalysed addition of HBr occurs
through a free radical addition rather than a
polar electrophilic addition.
- also observed for the reaction between HBr
and many different alkenes.
- not observed with HF, HCl or HI.
Formation of anti-Markovnikov alcohol
• Alkenes goes to hydroboration reaction to form antiMarkovnikov alcohol.
H2O2, -OH
B2H6
C C
C C
H OH
anti-markovnikov
examples:
CH3CH=CH2
H2O2, -OH
B2H6
CH3CHCH2-OH
propene
CH3
CH3 C CH2
propanol
B2H6
CH3
H2O2, -OH
CH3 CH CH2 OH
isobutyl alcohol
isobutylene
CH3
CH3 CH C CH3
2-methyl-2-butene
-
B2H6
H2O2, OH
CH3
CH3CHCHCH3
OH
3-methyl-2-butanol
Combustion of alkenes:
 The alkenes are highly flammable and burn
readily in air, forming carbon dioxide and
water.
 For example, ethene burns as follows :
C2H4 + 3O2 → 2CO2 + 2H2O
OXIDATION
• Oxidation: reactions that form carbonoxygen bonds.
• Oxidation reaction of alkenes:
i) epoxidation
ii)hydroxylation
iii)Ozonolysis
EPOXIDATION OF ALKENES
• Epoxide / oxirane: a three-membered cyclic ether.
O
C C
R C
alkene
O
C C
O OH
peroxyacid
O
R C OH
epoxide (oxirane)
acid
• Examples of epoxidizing reagent:
O
CH3 C O O H
peroxyacetic acid
O
C O O H
peroxybenzoic acid
(PhCO3H)
O
Cl
O
H
O
m-chloroperoxybenzoic acid
(MCPBA)
Examples:
MCPBA
o
O
CH2CI2, 25 C
cyclohexene
1,2-epoxycyclohexane
MCPBA
o
O
CH2CI2, 25 C
cycloheptene
1,2-epoxycycloheptane
HYDROXYLATION OF ALKENES
• Hydroxylation:
- Converting an alkene to a glycol requires adding a
hydroxyl group to each end of the double bond.
• Hydroxylation reagents:
i) Osmium tetroxide (OsO4)
ii)Potassium permanganate (KMnO4)
C C
OsO4
H2O2
(or KMnO4, -OH)
C C
OH OH
glycol
CH2
CH2
KMnO4 (aq), OHcold, dilute
ethene
CH2 CH2
MnO2
OH OH
1,2-ethanediol
CH3 CH CH2
KMnO4 (aq), OHcold, dilute
propene
CH3 CH CH2
OH OH
1,2-propanediol
* Also known as Baeyer’s test
MnO2
OZONOLYSIS OF ALKENES
• Ozonolysis:
- The reaction of alkenes with ozone (O3) to form an ozonide, followed
by hydrolysis of the ozonide to produce aldehydes and /or ketone.
- Widely used to determine the position of the carbon-carbon double
bond.
- Ozonolysis is milder and both ketone and aldehydes can be
recovered without further oxidation.
R
R'
O3
C C
R
H
R
O
R'
(CH3)2S
C C
R O O H or H2O, Zn/H+
ozonide
R
R'
C O
R
ketone
O C
H
aldehyde
EXAMPLES:
i) O3
ii) (CH3)2S
3-nonene
CH3O
H
OCH3
H
i) O3
ii) (CH3)2S
O
H
O
CH3O
H
OCH3
O
O
O
O
H
H
REACTIONS OF ALKENES WITH HOT, ACIDIFIED
KMnO4
R
R'
C C
R''
R''
H
R'
C O
R
O C
R''
OH
ketone
C C H
OH OH
R
R''
R R'
KMnO4/H+
C O
O C
H
aldehyde
ketone
acid
R CH=CH2
R'
KMnO4/H+
R COOH + CO2 + H2O
Example:
+
KMnO4/H
C
4-methyl-4-octene
O
2-pentanone
HO
C
O
butanoic acid
POLYMERIZATION OF ALKENES
• Polymer: A large molecule composed of many smaller
repeating units (the monomers) bonded together.
• Alkenes serves as monomers for some of the most
common polymers such as polyethylene (polyethene),
polypropylene, polystyrene, poly(vinyl chloride) and
etc.
• Undergo addition polymerization /chain-growth
polymer:
- a polymer that results from the rapid addition of one
molecule at a time to a growing polymer chain, usually
with a reactive intermediate (cation, radical or anion) at
the growing end of the chain.
repeating unit
CI
H
H
H
H
vinyl chloride
CI
C C
C C
C C
H
CI
H
H
H
H
H
CI H
Cl H
Cl
C
C
C
C
C
C
H
H
H
H
H
H
n
poly(vinyl chloride)
SOME OF THE MOST IMPORTANT ADDITION POLYMERS
POLYMER
Polyethylene
Polypropylene
POLYMER USES
Bottles, bags,
films
Plastics, olefin
fibers
MONOMER
FORMULA
POLYMER
REPEATING UNIT
CH2=CH2
CH2 CH2 n
H
CH3
C
C
H
Polystyrene
Plastics, foam
insulation
H
CH2 CH n
H
C C
Poly(isobutylene) Specialized
rubbers
CH3
H
H
H
CH3
H
C C
CH3
H2C C
H
n
CH3
CH2 C
CH3
n
UNSATURATION TESTS FOR ALKENES
1) Reactions of alkenes with KMnO4
- KMnO4 is a strong oxidising agent.
- alkenes undergo oxidation reactions with
KMnO4 solution under two conditions:
a) Mild oxidation conditions using cold,
dilute, alkaline KMnO4 (Baeyer’s test).
b) Vigorous oxidation conditions using hot,
acidified KMnO4.
a) Reaction of alkenes with cold, dilute, alkaline
KMnO4 (Baeyer’s test)
- the purple colour of KMnO4 solution disappears
and a cloudy brown colour appears caused by the
precipitation of manganese (IV) oxide, MnO2.
- test for carbon-carbon double or triple bonds.
- a diol is formed (containing two hydroxyl groups
on adjacent carbon atoms).
-
C C
KMnO4 (aq), OH
cold, dilute
C
C
OH OH
a diol
MnO2
2)
Reactions of alkenes with bromine
- A solution of bromine in inert solvent (CH2CI2 or CCI4)
and dilute bromine water are yellow in colour.
- The solution is decolorised when added to alkenes or
organic compounds containing C=C bonds.
C C
Br2
CH2CI2
C
C
Br Br
C C
Br2(aq) H2O
C
C
OH Br
C
C
Br Br
DETERMINATION OF THE POSITION OF THE
DOUBLE BOND
a) Ozonolysis of alkenes:
- For example, ozonolysis of an alkene produces
methanal and propanone.
CH3
H
H C O
methanal
O
C CH3
propanone
remove the oxygen atoms from the carbonyl compounds and
joining the carbon atoms with a double bond.
H
H C
CH3
C CH3
H
H
CH3
C
C CH3
2-methylpropene
b) Reaction of alkenes with hot, acidified KMnO4
- by using hot, acidified KMnO4, the diol obtained is
oxidised further.
- cleavage of carbon-carbon bonds occurs and the
final products are ketones, carboxylic acids or
CO2.
CH3
CH3 C CH2
2-methylpropene
KMnO4/H+
CH3
CH3 C O
propanone
(ketone)
CO2
+ H2O
• Example:
An alkene with the molecular formula C6H12 is oxidised with
hot KMnO4 solution. The carboxylic acids, butanoic acid
(CH3CH2CH2COOH) and ethanoic acid (CH3COOH), are
produced. Identify the structural formula of the alkene.
i) cleavage of the double bond gives a mixture of carboxylic acids
H H
R C C R'
KMnO4/H+
OH
OH
R C
O
O C R'
ii) location of the double bond is done by taking away the oxygen atoms from the
carboxylic acids and then joining the carbon atoms by the double bond.
RCOOH and R'COOH
CH3CH2CH2COOH
butanoic acid
and
RCH=CHR'
CH3COOH
ethanoic acid
CH3CH2CH2CH=CHCH3
2-hexene
USES OF ALKENES
• Ethylene and propylene are the largest-volume industrial
organic chemicals.
• Used to synthesis a wide variety of useful compounds.
H H
H H n
CH2
ethylene oxide
H
+
H 2O
CH2 CH2
OH
OH
ethylene glycol
CH3 C OH
H
acetaldehyde
polymerize
H 2C
oxidize
CH3 C
polyethylene
O
O
O
C C
acetic acid
oxidize
O2
H
Ag catalyst
H
H
C C
ethylene
H
Cl2
CH2 CH2
CI CI
ethylene dichloride
H 2O
catalyst
CH3 CH2
OH
ethanol
NaOH
H
H C
CI
C H
vinyl chloride
POLYETHENE (PE)
• The most popular plastic.
• Uses:
i) Grocery bags
ii)Shampoo bottles
iii)Children's toy
iv)Bullet proof vests
v)Film wrapping
vi)Kitchenware
POLYVINYL CHLORIDE (PVC)
HH
H C C CI
vinyl chloride
polymerize
H
C
H
CI H
C C
H H
CI H
C
C
H n H
poly(vinyl chloride)
PVC, "vinyl"
CI
C
H
USES OF PVC:
 Clothing
- PVC fabric has a sheen to it and is waterproof.
- coats, shoes, jackets, aprons and bags.
 As the insulation on electric wires.
 Producing pipes for various municipal and industrial
applications. For examples, for drinking water distribution
and wastewater mains.
 As a composite for the production of accessories or
housings for portable electronics.
 uPVC or Rigid PVC is used in the building industry as a
low-maintenance material.
 Ceiling tiles.
USES OF ETHANOL
• Motor fuel and fuel additive.
• As a fuel to power Direct-ethanol fuel cells (DEFC) in order to
produce electricity.
• As fuel in bipropellant rocket vehicles.
• In alcoholic beverages.
• An important industrial ingredient and use as a base chemical
for other organic compounds include ethyl halides, ethyl
esters, diethyl ether, acetic acid, ethyl amines and to a lesser
extent butadiene.
• Antiseptic use.
• An antidote.
• Ethanol is easily miscible in water and is a good solvent.
Ethanol is less polar than water and is used in perfumes,
paints and tinctures.
• Ethanol is also used in design and sketch art markers.
• Ethanol is also found in certain kinds of deodorants.