Organic Chemistry
11 – The Alkenes
Leaving Certificate Chemistry
The Alkenes: CnH2n
Ethene: C2H4
2 Carbon
Longest
Chain
Carbon-Carbon
double Bond
Only
H
H
C
H
C
2 planar
carbons
H
The Alkenes: CnH2n
These
are
also
constituents of crude
oil
Ethene – C2H4
The first member is
2002 Q. 6 (a) (8)
ethene
These compounds
are not soluble in
water
The Alkenes: CnH2n
Propene: C3H6
3 Carbon
Longest
Chain
Carbon-Carbon
double Bond
Only
H
H
C
C
2 planar
carbons
H
H
C
H
2005 Q. 4 (i) (6)
Tetrahedral
carbon
H
The Alkenes: CnH2n
Butene: C4H8
4 Carbon
Longest
Chain
Carbon-Carbon
double Bond
Only
H
C
H
Tetrahedral
carbon
H
H
H
C
C
C
H
H
2 planar
carbons
H
The Alkenes: CnH2n
These
are
also
constituents of crude
oil
Ethene – C2H4
The first member is
2002 Q. 6 (a) (8)
ethene
These compounds
are not soluble in
water
The Alkenes
Functional Group: C = C
All of these molecules are unsaturated
molecules – They will decolourise
bromine water and acidified potassium
permanganate solution
An unsaturated organic compound
is a compound that contains one or more
double or triple covalent bonds
2008 Q. 9 (c) (6)
Definition
2004 Q. 2 (d) (6)
3 Isomers of C4H8
2008 Q. 9 (b) (12)
2006 Q. 9 (d) (12)
Methyl Group
H
H
C
H
H
H 3 H
CH
1
2
3
C
C
C
H
H
2 – methylprop
But – 2
1 - ene
– 1 - ene
H
Isomers of butene
But-1-ene
But-2-ene
2-methylpropene
Preparation of Ethene
2006 Q. 9 (b) (6)
Ethanol
C2H5OH
Aluminium
Oxide [catalyst]
Al2O3
Ethanol
Structural Formulae
Ethanol: C2H5OH
-OH Group
Other Uses
2 Carbon
Longest
Chain
C6H12O6
Glucose
Present
H
H
C
H
2C2H5OH + 2 CO2
C
OH
Ethanol
Produced in industry
by
fermentation
H
H
Fuel
Solvent Thermometer
Balanced Equation
H
H
H
H
C
H
C
H
C
H
Ethanol
C
OH
Aluminium Oxide H
[catalyst]
Al2O3
This is an elimination reaction
1.Formation of an
unsaturated compound
2.Loss of a small molecule
like water
H
Ethene
H2O
Water
2007 Q. 8 (a) (6)
Preparation of Ethene
Balanced Equation for the Synthesis of Ethene
C2H5OH
Ethanol
Al2O3
C 2H 4
Ethene
+
H 2O
Water
Preparation of Ethene
Aluminium
Oxide is placed
halfway along
the boiling tube
Ethanol
soaked
in glass
wool
Heating
the
catalyst using a
Bunsen
Collecting
ethene by the
downward
displacement of
water
Preparation of Ethene
2006 Q. 9 (b) (3)
2004 Q. 2 (a) (5)
The ethanol is soaked in glass wool with
the glass wool being placed in after the
ethanol so as to ensure that all of the
liquid is soaked up.
Preparation of Ethene
The first couple of
test tubes collected
are usually discarded
as
they
contain
displaced air from
the reaction boiling
tube.
Preparation of Ethene
Be careful of suckback
If this occurs:
1. Remove the delivery tube from
the boiling tube
2. Apply heat
Preparation
of
Ethene
Ethene is
Ethene Reaction with acidified potassium permanganate
Pink
Colourless
Ethene Reaction with bromine water
Yellow
Colourless
These tests prove that ethene is an
unsaturated compound
Preparation
of
Ethene
Ethene is
Ethene burns with a luminous flame
Burning any hydrocarbon produces carbon
dioxide and water vapour
Balanced Equation for the Combustion of Ethene
C 2H 4
+
3 O2
Turns Limewater Milky
2CO2
+
2 H 2O
Turns blue cobalt
chloride paper pink
The uses of Ethene
Ethene is commonly used in industry to
ripen fruit and produce the useful plastic
polythene
Ethene is
Chemical Reactions
of The Alkenes
Addition of Hydrogen
Hydrogen
Nickel Catalyst
Addition
The Alkenes
e.g. Ethane
C2H6
e.g. Ethene
C2H4
H
The Alkanes
H
H
C
C
H
H
H
C
+
C
H
H2
H
Ethene
Hydrogen
H
H
Ethane
Important Industrial Reaction
Used to convert vegetable oils, which are unsaturated, into solid
saturated materials used in margarine and dairy products.
Addition of Hydrogen
H
H
C
C
H
C
H
Propene
H
H
H
H2
Hydrogen
H
H
H
C
C
C
H
H
H
Propane
H
Addition of Hydrogen
H
H
H
H
H2
C
H
C
Butene
H
C
C
H
H
H
H
H
H
H
C
C
C
C
H
H
H
H
Butane
Hydrogen
H
Uses of hydrogenation
reactionsions
• Unsaturated fats
Saturated fats
Addition of Chlorine
The Alkenes
Ionic Addition Mechanism
e.g. Ethene
C2H4
H
The Chloroalkanes
e.g. 1, 2 - Dichloroethane
C2H4Cl2
Cl
Cl
C
C
H
H
H
C
+
C
H
Cl2
H
Ethene
Chlorine
H
H
1, 2 - Dichloroethane
Important Industrial Reaction
1, 2 – Dichloroethane is used to produce chloroethene which is used to
produce the very important plastic PVC
1,2 dichloroethane is used to
make PVC
Addition of Chlorine
H
H
C
C
H
C
H
Propene
H
H
H
Cl2
Chlorine
H
H
H
C
C
C
Cl
Cl
H
1, 2 -dichloropropane
H
Addition of Chlorine
H
H
H
C
C
C
H
C
H
H
Cl2
Chlorine
Butene
1, 2 dichlorobutane
H
H
H
H
H
H
H
C
C
C
C
Cl
Cl
H
H
H
Addition of Bromine
Ionic Addition Mechanism
H
H
C
+
C
H
Br2
H
Ethene
Bromine
H
Br
Br
C
C
H
H
H
1, 2 - dibromoethane
Important Industrial Reaction
1, 2 – Dibromoethane is used to prevent poisonous lead
accumulating in cars
Addition of Bromine
H
H
C
C
H
C
H
Propene
H
H
H
Br2
Bromine
H
H
H
C
C
C
Br
Br
H
1, 2 -dibromopropane
H
Addition of Bromine
H
H
H
C
C
C
H
C
H
H
Br2
Bromine
Butene
1, 2 dibromobutane
H
H
H
H
H
H
H
C
C
C
C
Br
Br
H
H
H
Addition of Water
Water (Steam)
Addition
The Alkenes
The Primary Alcohols
e.g. Ethanol
C2H5OH
e.g. Ethene
C2H4
H
H
C
C
H
+
H
Ethene
H2O
H
H
H
C
C
H
H
OH
Ethanol
Important Industrial Reaction
Used to produce the important solvent ethanol
Addition of Water
H
H
C
C
H
C
H
Propene
H
H
H
H2O
Water
2002 Q. 6 (d) (6)
H
H
H
C
C
C
H
H
H
Propanol
OH
Addition of Water
H
H
H
H
H2O
C
H
C
Butene
Butanol
H
C
C
H
H
H
H
H
H
H
C
C
C
C
H
H
H
H
Water
OH
Uses of Hydration reactions
Used to make alcohols, which are useful
solvents for chemical reactions
Addition of Hydrogen Chloride
The Alkenes
e.g. Ethene
C2H4
H
The Chloroalkanes
Ionic Addition Mechanism
e.g. Chloroethane
C2H5Cl
HCl
H
C
C
H
+
H
Ethene
HCl
H
H
H
C
C
H
H
Chloroethane
Cl
Addition of
Hydrogen Chloride
H
H
C
C
H
H
H
H
H
C
C
H
Cl
Ethene
Chloroethane
HCl
Hydrogen Chloride
H
Chloroethane – used as a
binding agent in paint
H
Addition of
Hydrogen Chloride
H
H
C
C
H
Propene
C
H
H
Cl
H
H
H
C
C
C
H
H
H
HCl
Hydrogen
Chloride
chloropropane
H
Addition of
Hydrogen Chloride
H
H
H
C
C
C
H
C
H
Butene
chlorobutane
H
H
H
HCl
Hydrogen
Chloride
H
H
H
H
H
C
C
C
C
Cl
H
H
H
H
Polymerisation of Ethene
H
H
C
H
H
H
C
Ethene
H
C
H
H
H
H
C
Ethene
H
H
2008 Q. 9 (e) (6)
C
C
C
C
Polythene
H
H
H
H
n
Polymerisation of ethene
H
H
C
C
H
+
H
H
H
C
C
H
Ethene
H
Ethene
H
H
H
H
C
C
C
C
H
H
H
H
Polyethene
n
Important Industrial
Reaction
Used to produce the very
important plastic polythene
Polymerisation of Propene
H
H
C
H
H
H
C
Propene
C
CH3
H
C
Propene
H
H
H
H
C
C
C
C
CH3
Polypropene
H
CH3
H
CH3
n
Using Polymerisation to make
Polyvinylchloride PVC – step 1
H
H
C
C
H
H
Ethene
H
Cl2
Chlorine
H
H
C
C
Cl
Cl
H
1, 2 -dichloroethane
Using Polymerisation to make
Polyvinylchloride PVC – step 2
H
H
H
C
C
Cl
H
C
H
Cl
1, 2 dichloroethane
Cl
H
C
H
chloroethene
Using Polymerisation to make
Polyvinylchloride PVC – step 3
H
H
Cl
C
C
C
H
H
Cl
C
H
H
H
H
H
H
C
C
C
C
PVC
H
Cl
H
Cl
n
PVC WINDOWS
Substitution
using UV Light
The Alkanes
Ethane C2H6
+ H2
- H2
The Chloroalkanes
Chloroethane C2H5Cl
The Alkenes
+ HCl , + Cl2
Ethene C2H4
+ H2O
- H2O Aluminium Oxide
Catalyst
The Polymers
Polythene & Polypropene
The Alcohols
Ethanol C2H5OH