BY
MAHWASH HAFEEZ
 Alkenes are hydrocarbons that contain a carbon –
carbon double bond (with no functional groups, only
substituents present).
 They are also called “Olefins”.
 They are characterized by molecular formula CnH2n.
 They are said to be unsaturated (having double
bond).
 They are also called aliphatic hydrocarbons ( chain
compounds)
SOME IMPORTANT TERMS
FOR NAMING ALKENES





For naming the alkenes sytematically first we
have to study about the following four
features:
(a) Root word
(b)Primary suffix
(c)Secondary suffix
(d)Prefix
ROOT WORD:(PARENT CHAIN/MAIN CHAIN)
It means the carbon chain. Some commonly used
root words in alkenes are:
Chain length
Root Word

C1
Meth
C2
Eth
C3
Prop
C4
But
C5
Pent
C6
Hex
C7
Hept

C8
Oct
C9
Non
C10
Dec-
Primary Suffix:
The primary suffixes are added to the root word to
show unsaturation(double bond) in a carbon chain.
Name of Carbon Chain
Unsaturated
(CH2 ═ CH2)
Primary Suffix
-ene
IUPAC name
Alkene
PREFIX








Prefixes are added to the root word to indicate the
presence of one or more substituents on the main carbon
chain. These prefixes include:
fluoro(-F)
Chloro(-Cl)
bromo(-Br)
Iodo(-I)
Nitro(-NO2)
Alkoxy(-O-R)
Alkyl groups
Arrangement of Prefixes, Root word
and Suffixes


The prefixes, root words, primary and secondary suffixes
are arranged as follows while writing the name of an
alkene.
IUPAC name = Prefixes + Root word + Primary
Suffix + Secondary suffix
RULES FOR NAMING ALKENES
The base or parent chain of alkene is determined by the
longest chain of carbon atoms containing the double bond in
the formula. The longest chain may be bend or twist. It is
seldom horizontal.
CH3
CH3-CH2-CH2-CH2-CH
|
║
CH3-CH2-CH2
CH
CH
|
║
|
CH3-CH2-CH-CH2-C-CH3
CH3
7 CARBON CHAIN
8 CARBON CHAIN
If the chain contain only double bond and no other
substituents, the chain is numbered starting from the
Carbon closest to the double bond and the double bond is
given the lower number of its two double-bonded carbon
atoms.
1- Butene
OR
But – 1 – ene
• A compound with two double bonds is a diene. A triene
has three double bonds and a tetraene has four bonds.
• Numbers are used to specify the locations of the double
bonds.
1,3-butadiene
buta-1,3-diene
If one substituent or functional group is attached to the
parent chain, then numbering should start from the side to
give minimum number to the sum of substituent and the
double bond. e.g.
1
CH2
║
8CH -7CH -6CH
2 CH
3
2
2
|
|
5CH -4CH -3CH-CH
2
2
3
The name of this compound is 3- methy-l- octene or
3- methyl-oct-1-ene. We will start the numbering from
right side because from right side the sum of the
numbers of carbon containing substituent and the double
bond is 1+3=4 but from left side it is 6+8=14.
EXAMPLES
Name the following alkene according to IUPAC system
2,3-dimethyl-1-pentene
2,3-dimethyl-pent-1-ene
2,5- dimethyl – 1,3 – heptadiene
2,5- dimethyl – hepta – 1,3- diene
2 – methyl - 1,3,6-octatriene
2 – methyl - octa-1,3,6-triene
3-ethyl-1-heptene – 5 - ol
3-ethyl-hepta-1-ene – 5 - ol
6-chloro-4-ethyl-6-methyl-1,4-heptadiene
6-chloro-4-ethyl-6-methylhepta-1,4-diene
SYNTHESIS OF ALKENES
1. Dehydrohelogenation of alkyl halides:
Alkenes can be prepared by the removal
of a hydrogen and a halogen (i.e. hydrogen halide) from an
alkyl halide by heating.
CH3 – CH2 – Cl
CH2 ═ CH2+ HCl
2. Dehydration of alcohols:
Alkenes can be prepared by the removal
of a water molecule from an alcohol.
CH3 – CH2 – CH2 – OH
CH3 – CH ═ CH2+ H2O
3. Hydrogenation of alkynes:
Alkenes can be prepared by hydrogenation
of alkynes in the presence of a catalyst.
Pd(BaSO )
CH ≡ CH Quinoline4 CH2 ═ CH2
4. Dehalogenation of vic – dihalides:
Alkenes can be prepared by the removal
of a halogen from vic-dihalide(compounds in which
halogens are attached to adjacent carbon atoms) by treating
it with Zn dust in an anhydrous (containing no water)
solvent like methanol or acetic acid.
PHYSICAL PROPERTIES OF
ALKENES
 Physical
State:
Alkenes with 1-4 Carbon atoms are gases.
Alkenes with 5-17 Carbon atoms are volatile liquids.
Alkenes with more than 18 Carbon atoms are solids.
 Melting & Boiling Point:
Alkenes usually have low melting and boiling points.
 Solubility:
Alkenes being weekly polar, are soluble in nonpolar solvents such as CCl4, ether and benzene. They are
generally insoluble in water.
 Density:
The density of liquid alkenes increases slightly
with increase in the size of the molecules due to the
increasing intermolecular van der Waals’ forces
which cause the alkenes to be more compact in the
condensed liquid state.
 Reactivity:
Alkenes are relatively reactive as compared to
alkanes.
REACTIONS OF ALKENES
1. Hydrogenation:
A molecule of hydrogen can be added to an
alkene under moderate pressure (1-5atm) in the presence of
a catalyst to produce an alkane.
CH2═CH2 + H2
a catalyst
1 – 5 atm
CH3 – CH3
2. Halogenation:
Alkenes can readily react with halogens in an inert
solvent at room temperature to give vic. Dihalide.
CCl4
CH2═CH2 + Br2
CH2Br – CH2Br
3. Hydartion:
Alkenes react with water to form alcohols.
CH3 – CH═CH2+ H – OH H2SO4 CH3 – CH – CH3
|
OH
4. Hydrohalogenation:
Alkenes react with hydrogen halides to form
haloalkanes.
CH2═CH2 + HX  CH3 – CH2 – X
Mechanism:
H
H
H H
H H
C=C
H–C+–C–H
H– C–C–H
H
H
H
Br H
+
H – Br
Br-:
5. Oxidation:
It can be done in two ways:
a) Epoxidation:
Alkenes react with peroxyacids to form cyclic ethers
called epoxides. O
O
O
║
║
CH2═CH2+CH3–C–O–OHCH2
CH2 + CH3–C–OH
Peracetic acid
Ethylene oxide
b) Ozonolysis:
Alkenes react with ozone (O3) to form ozonides.
O–O
CH2 ═CH2 + O3  CH2
CH2
O
An Ozonide
6. Polymerization:
Alkenes can be polymerized at high temperature to
give alkanes.
n(CH2═CH2)  –( CH2 – CH2)n–
Formation of polymers :
heat
CH2 = CH2
ethylene
CH3
CH = CH2
propene
Cl
CH = CH2
vinyl chloride
pressure
heat
pressure
heat
pressure
[CH2 - CH2]n
polyethylene
CH3
CH2 - CH2 n
polypropylene
Cl
CH2 - CH2 n
polyvinyl chloride
Medical uses of polymer
1) Heart valves
2) Blood vessel
3) Surgical mesh
4) Disposable syringes
5) Drug containers
6) Polyethylene is used in formation of food bags
7) Polypropylene is used in formation of water containers
and breast implants
8) Polyvinyl chloride is used as coating material (toxic)
1) Natural polymer : starch, cellulose, rubber, protein
2) Synthetic polymer: plastic, nylon, rayon, Dacron and
poly ethylene
This pattern repeats itself over and over again

Polypropylene