HALO ALKANES AND HALO ARENES ppt

OBJECTIVES
After studying this unit, STUDENTS will be able to
• Name haloalkanes and haloarenes according to the IUPAC
system of nomenclature from their given structures;
• Describe the reactions involved in the preparation of
haloalkanes and haloarenes and understand various
reactions that they undergo;
• Correlate the structures of haloalkanes and haloarenes with
various types of reactions;
• Use stereochemistry as a tool for understanding the reaction
mechanism;
• Appreciate the applications of organo-metallic compound;
• Highlight the environmental effects of polyhalogen
compounds.
1

OUTLINE
1. INTRODUCTION,CLASSIFICATION,
NOMENCLATURE
2. PHYSICAL PROPERTIES OF HALO
ALKANES & HALO ARENES
3. METHODS OF PREPARATION
4. CHEMICAL PROPERTIES
5. OPTICAL ISOMERISM
6. SN1 & SN2 REACTIONS
7. POLY HALOGEN COMPOUNDS
2

What is meaning of haloalkane?
Organic compounds formed by replacement of one or
more hydrogen atom/s by halogen atom/s. from
Hydrocarbon
Ex: chloromethane, Dichloromethane etc.
3

What is meaning of haloarene?
If one or more hydrogen is displaced by
halogen atom/s in aromatic ring ,
product is called as Haloarenes
5

Importance of Halogen
derivative.
Haloderivative Organic compounds have
many importance for Mankind:
1.As solvents for non-polar compounds.

2.Chloramphenicol
(medicine) to treat typhoid
fever.
7

3.Chloroquine
(medicine) used
to treat malaria.
4. Some fluorinated
compounds are being
developed as blood substitute
in surgery.
8

5.Halothane is used as anaesthatic during
surgery.
9

6.THYROXINE is used in the treatment of
Goitre disease
10

7. As starting materials for synthesis of
many compounds.
11

Based on
Number of
Halogen atoms
Monohalogen
Dihalogen
Polyhalogen
Based on the hybridisation of C−atom
of C−X bond of monohalocompounds
Compounds
containing sp3 C−X
bond (X = F, Cl, Br, I).
Compounds containing
sp2 C−X bond
Classification of Haloderivatives
13

Compounds containing sp3 C−X
bond (X = F, Cl, Br, I).
18

Compounds containing sp2
C−X bond (X = F, Cl, Br, I).
24

Vinylic halides
Halogen atom is bonded to a sp2 hybridised carbon
atom of a carbon-carbon double bond (C = C).
28 June 2020 2525
NVS HYD RO

Aryl halides
Halogen atom is directly bonded to the sp2
hybridised carbon atom of an aromatic ring.
2626

PREFIXES
• F Floro
• Cl Chloro
• Br Bromo
• I Iodo
WORD
ROOT
• 1C meth
• 2C eth
• 3C Prop
PRIMARY
SUFIXES
• ane
• ene
• yne
ORDER OF NAMING HALOGEN COMPOUNDS
2828

prop
1
2
3
1-Bromo + +ane
1-Bromopropane
2929

32
Solution
Name the following:
bromocyclopentane
1,3-dichlorocyclohexane
Br
Cl
Cl

WRITE IUPAC AND COMMON NAMES OF
FOLLOWING COMPOUNDS
28 June 2020 43

WRITE IUPAC AND COMMON NAMES OF
FOLLOWING COMPOUNDS
28 June 2020 44

Nature of C-X bond
Now THINK why of the following:
1. The C-X bond in haloalkanes is polar in nature.
2. C-X bond length increases as C-F< C-Cl < C-Br <C-I.
3. C-F bond is less reactive as compared to C-I bond.
4. Order of Dipole moment is CH3-Cl > CH3-F> CH3Br >CH3I
5. The dipole moment of chlorobenzene is lower than that of
cyclohexylchloride.
45

DIPOLE MOMENT OF
HALOALKANES
28 June 2020 46

28 June 2020 55
Why do haloalkanes have
higher boiling points as
compared to their
corresponding alkanes?

PRACTICE QUESTIONS
1. Which isomer of C5H11Cl has the
highest boiling point and which has
the lowest boiling point? Explain your
answer.
2. Arrange the following in the order of
increasing density:
(i) CHCl3,CH2Cl2, CCl4,CH3Cl
(ii) C2H5Cl, C2H5I,C2H5Br 58

METHODS OF PREPARATION OF
ALKYL HALIDES
1. FROM ALKANE
2. FROM ALKENE
3. FROM ALCOHOL
4. BY HALOGEN EXCHANGE
METHOD
59

• https://www.youtube.com/watch?v=4yPjkR
LcauI
28 June 2020 NVS HYD RO 66

3. FROM ALCOHOL
67
Preparation of iodo and bromo derivative, reactivity of
halogen acid and alcohol.

Can phenols be converted
to aryl halides by Darzen’s
method?
28 June 2020 73

75
AgF, Hg2F2, CoF3 or SbF3 can
be used. 2 or more H atoms on
same c-atom.

With Iodine it is called
Simonini Reaction and we
get ester.

1.Nucleophilic substitution reactions
79

85
If we have alkyl halide in excess, all hydrogens
of NH2 gets replaced by alkyl group. This
reaction is called Hoffmann’s ammonolysis.

86
The nucleophiles that can attack through two different sites are known
as ambident nucleophiles.

SAYTZEFF’S RULE
"In dehydrohalogenation reactions, the
preferred product is that alkene which has
the greater number of alkyl groups attached
to the doubly bonded carbon atoms."
28 June 2020 91

PHENYL CARBOCATION
28 June 2020 92

Stereochemistry-II
Optical Isomerism
95

Constitutional
Differ in bond connectivity
Stereoisomers
Differ in three dimensional
arrangement
Isomers
Same molecular formula
96
OR STRUCTURAL ISOMERS

Configurational
Differ in groups or atoms
Conformational
Due to free rotation
Stereoisomers
Differ in three dimentsional arrangement
97
Temporarily different shapes of
same molecule
Geometric isomers

Ring Compounds
Nitrogen-nitrogen double bond
Carbon- nitrogen double bond
Carbon- carbon double bond
Geometrical
Due to restricted rotation
Optical
Due to Chirality
Configurational
Differ in groups or atoms
98
Is geometrical isomerism
possible in alkynes?

Optical Isomerism
Existence of two or more isomers of a
substance that differ in their optical activity
Optical activity : the property of a molecule
to rotate the plane of plane-polarized light.
99

Plane-polarized light
Plane polarized light
Electrical field
Magnetic field
Oscillating
electrical field
The plane polarized light has mutually
perpendicular electric and magnetic fields.
However, it is the electrical component
that is more significant 101

What is plane-polarized light ?
Ordinary light consists of oscillating
electrical and magnetic fields or waves
vibrating in all directions perpendicular to
the direction the light beam
102

On passing the ordinary light through a
device called Polarizer, its oscillations in all
but one direction are blocked and the light
emerging from the polarizer oscillates in
only one plane
This is called plane polarized light
P
o
l
a
r
i
z
e
r
104

An optically active substance interacts
with the plane polarized light in such a way
that the plane of light rotates.
P
o
l
a
r
i
z
e
r
Solution of
optically
active
substance
a
105

The solution of substances that rotates
the plane of a plane polarized light to the
right is called dextrorotatory and the
one that rotates it to the left is called
laevorotatory
Dextrorotatory : rotation to right
(The angle of rotation, a, is considered to be positive (+).)
Laevorotatory : rotation to left
(The angle of rotation, a, is considered to be negative (-).)
108

• https://www.youtube.com/watch?v=gRIqx
E_P7BA
28 June 2020 114

Optical isomerism is due to
chirality in a molecule
Cause of Optical Activity
115

Chirality (non-superimposibility of
mirror image) is a necessary and
sufficient condition for a molecule
to show optical activity
28 June 2020 116

M
I
R
R
O
R
NON-SUPER IMPOSABILITY
e.g., hands or gloves
117

A right hand cannot be
superimposed on a Left hand
118

The objects that can be superimposed on their
mirror image are achiral.
M
I
R
R
O
R
e.g., a butterfly
The objects that are superimposable on their
mirror images are said to be achiral.
119

A butterfly is symmetric- one half of its
body exactly overlaps its other half
120

R AND S CONFIGURATION
https://www.chemistrysteps.com/how-to-
determine-r-and-s-configuration/
28 June 2020 122

M
I
R
R
O
R
Bromochlorofluoromethane
28 June 2020 123

Non-superimposable hence chiral

28 June 2020 125
R= CH3, it is alanine

CHIRAL [ASYMMETRIC MOLECULES]
28 June 2020 126

M
I
R
R
O
R
Bromomethane
28 June 2020 128

The mirror image is superimposable hence
the molecule is achiral and does not show
optical isomerism
28 June 2020 129

 Compounds that are not superimposable
on their mirror images will show optical
isomerism
 One of the isomer is dextrorotatory
and the other is laevorotatory
 These isomers are called enantiomers
28 June 2020 130

In a pair of optically active enantiomers,each
enantiomer rotates the plane of polarized
light in equal and opposite directions.
P
o
l
a
r
i
z
e
r
Solution
of
Enantiomer
1
Solution
of
Enantiomer
2
However, a mixture of two in equal proportions
will be optically inactive and is called a racemic
mixture
28 June 2020 132

Recall the molecule of bromochlorofluoromethane
The carbon atom is attached to
four different groups.
Such a carbon atom is known as
asymmetric carbon atom.
A molecule possessing asymmetric
carbon atom shows enantiomerism.
Two optically active isomers (one dextro-
and other laevorotatory) exist
134

Nucleophilic Substitution
 A substitution reaction where the reagent
is a nucleophile
 A typical reaction of alkyl halides
 May follow SN2, SN1 and SNi mechanisms
 Depends on
 Nature of substrate
R X Nu R Nu X
+ +
 Reagent
 Reaction conditions
28 June 2020 136

SN1 Mechanism
SN1 : Substitution Nucleophilic
Unimolecular
Favoured
(R)3CX (R)3
COH HX
+ H2O +
With neutral or weak Nucleophiles
(water, alcohols)
28 June 2020 137

SN1 Mechanism
Unimolecular
Depends on alkyl halide and NOT nucleophile
Two steps
]
RX
[
Rate k
 ; Ist Order
Rate depends on conc. of ONE species
The first step is slow or Rate-determining
The second step is the fast step
28 June 2020 138

Step 1
Step 2
The SN1 Mechanism
R3C X
- X
R3
C
+
( slow)
Nu R3C Nu
R3
C +
+
(fast)
Cleavage of C-X bond (Formation of carbocation)
Attack of nucleophile (Formation of product)
28 June 2020 139

(CH3)3CBr (CH3)3COH
+ H2O + HBr
Doubling substrate conc. : Rate doubled
Doubling nucleophile conc. : Rate unchanged
Rate a [(CH3)3CBr]
Rate = k [(CH3)3CBr]
Example
Experimental facts
Thus
The SN1 Mechanism
28 June 2020 140

Positive Inductive Effect stabilises the positive
charge
 Reactive intermediates
Carbocations
C C
H
H
H
C
H
C H
H
H
C
H
H
H
C
H
H
H
C H
H
H
C
H
H
H
C
H
H
C H
H
H
> > > +
+
+ +
 Positively charged carbon
 Planar (sp2 hybridised)
28 June 2020 141

Carbocations are planar
Rate depends on stability of carbocation
(allylic, benzylic)
Nucleophile can attack
from both sides
Product is a racemic
mixture
Decrease in the order 3o > 2o > 1o
Resonance stabilised carbocations favoured
28 June 2020 142

Order of Reactivity in SN1
Directly related to the stability of
intermediate i.e. the Carbonium ion or the
Carbocation
The order of reactivity is
Tertiary > Secondary > Primary > Methyl
C
H
H
H +
C
R
H
H +
C
R
R
H +
C
R
R
R +
> > >
28 June 2020 143

SN2 : Substitution Nucleophilic Bimolecular
SN2 Mechanism
Favoured with strong nucleophiles
C
R
R
R
X HO C
R
R
R
HO Br
+ +
28 June 2020 144

C
R
R
R
X
HO C
R
R
R
X
HO


C
R
R
R
HO X
+
SN2 Mechanism
Bimolecular
nucleophile and substrate
Rate depends on the conc. of TWO species
28 June 2020 145

C
H
H
H
X HO C
H
H
H
HO Br
+ +
Experimental facts
]
OH
][
Br
CH
[
Rate 3

 k
Doubling nucleophile conc. : Rate doubles
Thus
Doubling substrate conc. : Rate doubles
28 June 2020 146

SN2 Mechanism
Attack of nucleophile and removal of
leaving group is simultaneous
One-step mechanism (Concerted )
Leaving group leaves OPPOSITE of the attacking
nucleophile
28 June 2020 147

Stereochemistry of SN2 Reaction
Attack from side opposite to the leaving group
Inversion of Configuration (Walden
inversion)
28 June 2020 148

Stereochemistry of SN2 Reaction
Attack from side opposite to the leaving group
Inversion of Configuration (Walden
inversion)
28 June 2020 149

Steric Effect in SN2 Reactions
Reactivity
150 1 0.01 0.0001
28 June 2020 152

Reaction with KCN and AgCN
CH3
CH2 Br KCN CH3
CH2 C N KBr
+
+
Propanenitrile
CH3
CH2 Br AgCN CH3
CH2 N C KBr
Propaneisonitrile
+
+
28 June 2020 153

SN1 Vs SN2
Bimolecular (one step)
Depends on nucleophile
and substrate
Favoured by strong
Nucleophiles
Mechanism
Unimolecular (two steps)
Rate of Reaction
Depends only on the
substrate
Nucleophiles
Favoured by neutral
Nucleophiles
28 June 2020 154

SN1 Vs SN2
Solvents
Favoured by polar
protic solvents
Favoured by Bulky
alkyl groups
Alkyl group
Favoured by polar aprotic
solvents
Favoured by less
substituted alkyl groups
Inversion of configuration
Stereochemistry
Racemic mixture
28 June 2020 155

Some Problems
1.Which one of the following will be faster
and why?
CH3OH + HBr
ii) CH3Br + CH3COO- CH3OCOCH3
i) CH3Br + HOH
28 June 2020 156

2. Arrange the following in increasing order of
reactivity towards SN1 reactions:
i) CH3CH2CH2Br, CH3CH2CH(Br)CH3, (CH3)3CBr
ii) (CH3)2CHBr , (CH3)2CHCl , (CH3)2CHI
28 June 2020 157

3. Arrange the following in increasing
order of reactivity towards SN2 reactions:
i) (CH3)2CHBr , (CH3)3CBr , CH3CH2Br
ii) CH3CH2Br , CH3CH2Cl , CH3CH2I
28 June 2020 158

PRACTICE PROBLEM
28 June 2020 159

Predict the order of reactivity of the
following compounds through SN
1
mechanisms:
n-Butyl bromide, n-Butyl chloride,
iso-Butyl bromide, sec-Butyl
bromide.

CHEMICAL PROPERTIES OF HALO
ARENES
28 June 2020 171

Reasons for the less rectivity of
chlorobenzene
28 June 2020 172

Reasons for the less rectivity
of chlorobenzene
28 June 2020 173

of chlorobenzene
28 June 2020 174

PHENYL CATION
28 June 2020 175

of chlorobenzene
28 June 2020 176

O- & p- directing
28 June 2020 177

NUCLOPHILIC SUBSTITUTION
REACTION
28 June 2020 178

NUCLOPHILIC
SUBSTITUTION REACTION
28 June 2020 179

NUCLOPHILIC
SUBSTITUTION REACTION
28 June 2020 180

1.HALOGENATION
28 June 2020 181

3.SULPHONATION
28 June 2020 183

4. FRIEDEL-CRAFTS
ALKYLATION
28 June 2020 184

REACTION WITH METALS
28 June 2020 186

4. FRIEDEL-CRAFTS
ALKYLATION
28 June 2020 187

REACTION WITH METALS
28 June 2020 188

POLY HALOGEN
COMPOUNDS
28 June 2020 189

Dichloromethane

Tetrachloromethane

Triiodomethane

Freons

DDT

SUMMARY
1. INTRODUCTION,CLASSIFICATION,
NOMENCLATURE
2. PHYSICAL PROPERTIES OF HALO
ALKANES & HALO ARENES
3. METHODS OF PREPARATION
4. CHEMICAL PROPERTIES
5. OPTICAL ISOMERISM
6. SN1 & SN2 REACTIONS
7. POLY HALOGEN COMPOUNDS
NVS HYD RO
28 June 2020 195

1. Why is sulphuric acid is not used during reaction of alcohols with
KI?
2. Arrange each set of compounds in order of increasing boiling
poings. i) Bromo Ethane , Bromoform, Chloro
methane, Dibromo methane
(ii) 1-Chloro Propane, Isopropyl chloride, 1-chloro butane
3. Predict the order of reactivity of the following compounds in SN1
& SN2 reactions. (i) The four isomeric bromo butanes
( ii) C6H5CH2Br, C6H5CH2 (C6H5 )Br, C6H5CH2 (CH3)Br,
C6H5CH2 (CH3 )(C6H5 )Br
4. Although Chlorine is an electron with drawing group yet it is orho
para directing in electrophilic aromatic substitution
reactions. Why?
5. Which alkyl halide from the following pairs would you expect to
react more rapidly by SN2 mechanism? Explain your
answer?
(A) CH3-CH2-CH2-CH2-Br & CH3-CH2-CHBr –CH3
(B)CH3-CH2-CHBr –CH3 & C(CH3)3Br
HOME WORK

6. alo alkanes react with KCN to form alkyl cyanides as main
product while AgCN forms isocyanides as the chief product.
Explain.
7. COMPLETE THE FOLLOWING
HOME WORK

HOME WORK
8. Explain the following named reactions
(a) Williamson’s synthesis (b) Swarts reaction
©Finkelstein reaction (d)Sand mayers reaction
(e) Gatterman reaction (f)Fittig reaction
9.What are ambident nucleophiles? Explain with an example.
10.What happens when
(i) n-butyl chloride is treated with alcoholic KOH
(ii) Bromobenzene is treated with Mg in the presence of dry ether
(iii) Chlorobenzene is subjected to hydrolsis.
(iv) Ethyl chloride is treated with aqueous KOH
(v) Methyl chloride is treated with KCN?
NVS HYD RO
28 June 2020 198

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