LECTURE NOTE SK025 (ORGANIC) KMKt

Step 2 : Formation of protonated alcohol

CH3

Step 3 : Deprotonation

H H CH3 + H ••O•• H H CH3
CC H
H CC H +
H :+O H
H OH

H H •O+• H
H
131

Reaction Mechanism : Acidified water

Example 2:

Write the mechanism for the major product for the
following reaction:

CH3 + H2O dilute H3PO4 OH
CH3–C–CH═CH2 CH3–C–CH2–CH3

CH3 CH3

132

Reaction Mechanism : Acidified water

Answer:

Step 1 : Formation of carbocation

CH3 •O+• CH3
CH3–C–CH═CH2 + H
slow + + H2O

H CH3–C–CH—CH3

CH3 H CH3

Step 2 : Rearrangement

CH3 1,2-methanide shift CH3

+ + 133

CH3–C–CH—CH3 CH3–C–CH—CH3
CH3
CH3
3o carbocation
2o carbocation

Reaction Mechanism : Acidified water

Step 3 : Formation of protonated alcohol

CH3 ••
+ •O•
+ H H fast
CH3–C–CH—CH3

CH3

Step 3 : Deprotonation

H •O•: + + H3O+

H 134

Learning Outcomes

(m) Explain the reaction of alkenes with:
i. O3 followed by Zn,H2O or O3 followed by
(CH3)2S (ozonolysis);
ii. hot, acidified KMnO4

(n) Predict the position of double bond through:
i. ozonolysis
ii. reaction with hot, acidified KMnO4

135

Oxidation

Ozonolysis

Reagent (i) O3 (ii) Zn, H2O @ (CH3)2S
Product aldehyde @ ketone

Example 1 :

CH3CH2CH═CHCH3 (i) O3 H
(ii) Zn, H2O CH3CH2C═O

+

H
O═CCH3

136

Ozonolysis

Example 2 : (i) O3 CH3 +
(ii) (CH3)2S CH3CH2C═O
CH3
CH3CH2C═CHCH3 H
O═CCH3

Example 3 : (i) O3 CH3 +
(ii) Zn, H2O CH3CH2C═O
CH3 137
CH3CH2C═CCH3 O═CCH3
CH3
CH3

Ozonolysis

Example 4 :

CH3 (i) O3 CH3
CH3CH2C═CH2 (ii) Zn, H2O
CH3CH2C═O + O═CH2

Example 5 :

H (i) O3 H
CH3CH2C═CH2 (ii) (CH3)2S
CH3CH2C═O + O═CH2

138

Reaction with hot, acidified KMnO4

Reagent KMnO4 / H+
Condition heat,
Product ketone & or carboxylic acid or CO2 & H2O

Example 1 :

CH3CH2CH═CHCH3 KMnO4 / H+ OH
CH3CH2C═O
∆
+
64
OH
O═CCH3

Reaction with hot, acidified KMnO4

Example 2 :

CH3 KMnO4 / H+ CH3 +
CH3CH2C═CHCH3 CH3CH2C═O
∆
OH
O═CCH3

Example 3 :

CH3 KMnO4 / H+ CH3 +
CH3CH2C═CCH3 CH3CH2C═O
∆ 140
CH3 O═CCH3
CH3

Reaction with hot, acidified KMnO4

Example 4 :

CH3 KMnO4 / H+ CH3
CH3CH2C═CH2
∆ CH3CH2C═O + CO2 + H2O

Example 5 :

H KMnO4 / H+ OH
CH3CH2C═CH2
∆ CH3CH2C═O + CO2 + H2O

141

EXAMPLE 1:

Write the structure of alkene that would produce
the following products when treated with ozone
followed by water, zinc and acid.

CH3COCH3 and CH3CH(CH3)CHO

EXAMPLE 2:

Deduce the structural formula of an alkene that
gives the following compound when it reacts with
ozone in the presence of Zn,H2O.

O=CH-CH2-CH2-CH(CH3)CH=O 142

Solution

1) CH3CH(CH3)CH=C(CH3)2
2)

143

EXAMPLE 3

• An unknown alkene with the formula C7H14
undergoes oxidation with hot acidic potasium
permanganate solution to form propanoic acid
and butanoic acid. What is the structure of this
alkene?

144

C7 H14 KMnO 4 / H+
Δ

O O
HC C
+ HC CH2 C
3 CH2 OH 3 CH2 OH

145

Solution

O O

H3C C OH H3C CH2CH2C OH
CH2 butanoic
acid
propanoic acid

HH 146

H3C CH2C C CH2CH2CH3
3-

EXAMPLE 4:

• An unknown alkene undergoes oxidation in hot
acidic KMnO4 to give the following product:

OO
CH3CCH2CH2CH2CH2C OH

Deduce the structural formula for the unknown
alkene.

Ans:

147

Chemical Test of
Alkenes

148

Learning Outcomes

o) Explain the unsaturation test for alkenes:
i. Baeyer’s test using dilute alkaline KMnO4 solution
ii. bromine in CH2Cl2
iii.bromine water

(Experiment 4: Reactions of Aliphatic and Aromatic Hydrocarbons)

p) Explain the preparation of synthetic polymers
through addition polymerisation (e.g.
polyethylene, poly vinyl chloride, polystyrene,
Teflon)

149

Unsaturation test for Alkenes

There are 3 chemical test to differentiate
between an alkanes and alkenes:

i) Baeyer’s test using cold,
dilute alkaline KMnO4 solution

Baeyer’s test

150

Unsaturation test for Alkenes

ii) Reaction with bromine
in CH2Cl2

iii)Reaction with bromine
water

Bromine test

151

Baeyer’s test using cold, dilute alkaline KMnO4

Reagent dilute KMnO4 / OH-

Condition cold

Product -diols

Baeyer’s test
Name of chemical test

Observation Purple colour of KMnO4
decolourised. Brown precipitate

formed.

64

Reaction with Cold, Basic KMnO4

Example :

dilute KMnO4/OH-

(i)

(ii) dilute KM/ nOOH4-/OH-

153

Reaction with Cold, Basic KMnO4

When the equation below are tested with cold, basic,
dilute KMnO4 ….

dilute KMnO4 /OH-

Name of chemical test : Baeyer’s test
Observations : Purple colour of KMnO4 decolourised.

Brown precipitate formed.

154

Bromine in Inert Solvent

Reagent Br2, CH2Cl2
Product vicinal dibromo
Name of chemical test Bromine test

Observation Reddish brown colour of bromine
decolourised

155

Bromine Test (Bromine in CH2Cl2)

C C + Br2 CH2Cl2
room temperature

(colourless) (reddish
brown)

CC
Br Br
(a colourless compou1n56 d)

• When bromine is used for this reaction,
it can serve as a test for the presence
of carbon-carbon double bonds.

• If bromine is added to alkene, the
reddish brown color of the bromine
disappears almost instantly as long as
the alkene is present in excess.

157

Bromine Water

Reagent Br2, H2O
Product halohydrin

Name of chemical test Bromine test

Observation Reddish brown colour of bromine
decolourised

158

Bromine test (Bromine water)

CC + Br2 /H2O temperature
(colourless)
room

(reddish

brown)

CC
Br OH
(a colourless compou1n59 d)

Example:

+H3C C CH2 Br2/H2O OH
H3C C CH2Br
CH3
CH3

160

PREPARATION OF SYNTHETIC POLYMERS

ADDITION
POLYMERISATION

• The addition reaction in which monomers with double
bonds are joined together by covalent bonds to form a
large molecule without a loss of smaller molecule.

• C=C are broken and replaced by C-C single bonds. This
enables chain formation to form the polymer.

• Peroxide is used as initiator in additional polymerisation

PREPARATION OF SYNTHETIC POLYMERS

ADDITION POLYMERISATION:
POLYETHYLENE

PREPARATION OF SYNTHETIC POLYMERS

ADDITION
POLYMERISATION:
POLYVINYL CHLORIDE, PVC

PREPARATION OF SYNTHETIC POLYMERS

ADDITION
POLYMERISATION:

POLYSTYRENE

PREPARATION OF SYNTHETIC POLYMERS

ADDITION
POLYMERISATION: TEFLON

EXERCISE:

1. Give the monomer structure for the following compound

a)

b)

2. Predict the structure of this polymer

ANSWER:

2 OR
.

OR

Summary chemical
reactions of
Alkene

168

CH3 CH3
CH3CH2C(OH)CH3 CH3CH2C(Br)CH3

i.O3
ii.Zn,H2O

Baeyer’s test Unsaturation test

169

Unsaturation test

LET’S TRY !

HBr

170

Edited By : Revised By :
KAD AO

Approved By :
ZA

CHAPTER 6 : BENZENE &
ITS DERIVATIVES

6.1 Introduction
6.2 Nomenclature
6.3 Chemical properties

Learning Outcomes

iii.
i.
ii.
iii.

Learning Outcomes

(a) Explain the electrophilic aromatic substitution reactions of benzene:

(C3,C4)

i. Nitration
ii. Halogenation
iii.Friedel-Crafts alkylation; and
iv.Friedel-Crafts acylation

(b) Illustrate the mechanism for the electrophilic aromatic substitution of
benzene. *limit to rection in 6.3(a) I,ii & iii only (C3,C4)

(c) Explain the influence of ortho-para and meta directing substituents
towards electrophilic aromatic substitution reaction. (C3)

(d) Predict the product of electrophilic aromatic substitution of
monosubstituted benzene. *limit to rection in 6.3(a) only (C3)

(e) Explain the following reactions of alkylbenzene: (C3)

i. oxidation with hot acidified KMnO4 or K2Cr2O7
ii. halogenation (free radical substitution)

6.1 INTRODUCTION
Describe :

• Aromaticity

• Kekulé structure

• Resonance structure of
benzene

Introduction

• In earlier time, compounds are called aromatic
because of their pleasant odours.

Benzene has strong
pleasant odour…

• Today, we use the word aromatic to refer to
benzene and its structural relatives.

Introduction

• Arenes are aromatic hydrocarbons that contain a
benzene ring as a structural unit.

• Benzene is the simplest aromatic hydrocarbon.

Example…

Benzene Naphthalene Toluene

Introduction

Aromaticity

4 structural criteria must be satisfied for compound
to be aromatic:

Introduction

CYCLIC

• To be aromatic, each p orbital must overlap
with p orbitals on adjacent atoms.

Introduction

PLANAR

All adjacent p orbitals must be aligned so that the
π electron density can be delocalized.