Haloalkanes and Haloarenes
6
“ The chapter delves into the realm of
haloalkanes and haloarenes, exploring their
chemical properties, preparation methods, and
reactions. These compounds play a vital role
across various industrial and medical fields.
They are employed in the manufacture of
solvents, anaesthetics, and refrigerants, among
other applications. This chapter not only offers
a deep understanding of the structural nuances
and reaction mechanisms of these halogen-
containing compounds but also highlights their
practical applications, such as in the synthesis
of complex organic molecules and in medical
treatments, enriching our understanding
of their significance in everyday life and
technological advancements. ”
SYLLABUS &
WEIGHTAGE
Years
List of Concept Names 2022
2020 2021 2023 2024
(Term-1)
Nomenclature, Preparation And Physical Properties of
Haloalkanes and Haloarenes – 2 Q* 1 Q (1 M) –
(Nomenclature, nature of C–X bond, physical properties)
Exam not conducted
Chemical Properties of Haloalkanes 3Q 4Q 4Q
(Chemical properties, optical rotation, mechanism of 5 Q*
substitution reactions.) (1 M Each) (1 M Each) (1 M Each)
Chemical Properties of Haloarenes and Polyhalogen
Compounds
(Nature of C–X bond, substitution reactions (Directive 2Q 2Q
1 Q (1 M) 2 Q*
influence of halogen in monosubstituted compounds only), (1 M Each) (1 M Each)
Uses and environmental effects of - dichloromethane,
trichloromethane, tetrachloromethane, iodoform, freons, DDT)
* All questions were of MCQ type and carried equal marks.
, ● Cd+ – Xd– On the basis of no. of Compounds containing Compounds containing
Halogen Atoms sp3 C – X bond sp2 C – X bond
● Halogen atoms are more elec-
tronegative than carbon, there- ● Monohalogen compounds : – ● Alkyl Halides : R – X ● Vinylic Halides :
fore, carbon-halogen bond of CH3 – X X
● Allylic Halides:
alkyl halide is polarised. ● Dihalogen compounds : X
X
CH2 –X
CH2 –X CH2X ● Aryl Halides :
X X
● Polyhalogen compounds : ● Benzylic Halides:
CH2 – CH – CH2 CH2X
Nature of C – X H 3C
X X X
bond
Classification
CONCEPT MAP
Colour and Smell
● Alkyl halides are colourless when pure. However, bromides and
Haloalkanes and iodides develop colour when exposed to light.
Physical Properties
Haloarenes Solubility
● Very slightly soluble in water.
Chemical Reaction with Metals Melting and Boiling Points
● B.pt of chlorides, bromides and iodides are considerably higher than the
191
Reactions Grignard Reagent hydrocarbons of comparable molecular mass.
dry
R – X + Mg RMgX ● The B.pt of isomeric haloalkanes decrease with increase in branching.
ether
Methods of ● Para isomers have high M.pt than ortho and meta isomers.
Wurtz Reaction
Preparation dry Density
R – X + 2Na + X – R R – R + 2NaX
ether ● Density increases with increase in no. of carbon atoms, halogen atoms
and atomic mass of the halogen atoms.
From Alcohols From Hydrocarbons From diazonium Salt
ZnCl2 (a) By Free Radical Halogenation NaNO2 + HX N+2X–
R – OH + HCl R – Cl + H2O NH2
3R – OH + PX3 3R – X + H3PO3 Cl2,UV 273-278 K
CH3CH2CH2CH3 CH3CH2CH2CH2Cl +
R – OH + PCl5 R – Cl + POCl3 + HCl CH3CH2CHClCH3 Benzene
diazonium
R – OH + SOCl2 R – Cl + SO2 + HCl↑ (b) By Electrophilic Substitution halide
Sandmeyer’s Reaction
Halogen Exchange CH3 CH3 CH3
Fe/Dark N+2X– X
+ X2 + Cu2X2
To Access One
(a) Finkelstein reaction: X X
+ N2
Scan This QR Code
Shot Revision Video
dry acetone o-Halotoluene p-Halotoluene
Aryl Halide
R – X + NaI R – I + NaX
N+2X– I
KI
(b) Swart’s reaction: + N2
CH3Br + AgF/Hg2F2/CoF2/SbF3 CH3F + AgBr
Haloalkanes and Haloarenes
P
W
,P
W
Aryl halides are extremely less reactive 1. Nucleophilic Substitution Reactions 3. Reaction With Metals
towards Nu–Sub. reactions due to: Replacement by Hydroxyl Group:- Wurtz Fittig Reaction
1. Resonance Effect Cl OH Cl OH dry ether
X+ Na + R – X R + NaX
2. Difference in Hybridisation of carbon
atom in C – X Bond. (i) NaOH, 623K (i) NaOH, 443K Fittig Reaction
(ii) H+ (ii) H+ X
3. Instability of phenyl cation
4. Because of possible repulsion it is less NO2 NO2 dry ether
likely for Nu– to approach e– rich arenes 2 + 2Na + 2NaX
diphenyl
Haloarenes
Haloalkanes and Chemical Nucleophilic
Haloarenes Reactions Substitution Reactions
2. Electrophilic Substitution Reactions
(i) Halogenation
Cl Cl Cl
Cl Unimolecular Nucleophilic Substitution Bimolecular Nucleophilic Substitution
Anhyd. FeCl3 Reaction (SN2)
+ Cl2 + Reaction (SN1)
CH3 H
+ H
192
Cl STEP 1 OH– + H Cl OH Cl
(CH3)3CBr H3C CH3 + Br– H
1, 4-dichloro- 1, 2-dichloro-
benzene benzene H H
H3 C + STEP II Nu– substrate
(ii) Nitration (major) (minor) H3 C
CH3 + ŌH (CH3)3C – OH
Cl H
Cl Rate ∝ [Substrate] OH
Cl H + Cl–
conc. HNO3 NO2 Reactivity = 3° > 2° > 1° > CH3 Rate ∝ [Nu–] [substrate] H
+ Racemisation occurs Reactivity = 3° < 2° < 1° < CH3
H2SO4, D
(minor) Inversion in configuration occurs
NO2
(iii) Sulphonation (major)
Cl Cl
Elimination Reactions Polyhalogen Compounds
SO3H Dichloromethane
conc. H2SO4
Cl + ● Paint Remover
D
● Propellants in Aerosols
(minor) H
SO3H B–: Trichloromethane
(major) b a ● Solvent for Fats
(iv) Friedel Craft’s Reaction C C C=C + B – H + X–
Iodoform
Cl Cl Cl X ● Antiseptic
O
COCH3 Saytzeff Rule | Zaitsev Rule : Freons
Anhyd. AlCl3 In dehydrohalogenation, the preferred product
+ CH3 – C – Cl + ● For aerosol propellants, refrigeration and air
is that alkene which has the greater number conditioning purposes.
(minor) of alkyl groups attached to the doubly bonded
COCH3 carbon atom. DDT
(major) ● As insecticides
, NOMENCLATURE, PREPARATION AND PHYSICAL
1 PROPERTIES OF HALOALKANES AND HALOARENES
NCERT Definitions (Commonly asked in 1 mark)
U Haloalkanes: Alkanes that have halogen atoms attached to the sp3 hybridized carbon of an alkyl halide.
U Haloarenes: Aromatic hydrocarbons that have halogen atoms attached to the sp2 hybridized carbon of an aryl halide.
U Allylic halides: In these types of halides, the halogen atom is bonded to an sp3 hybridized carbon atom which is adjacent to carbon
carbon double bond.
X Allylic carbon
U Benzylic halides: In these compounds, the halogen atom is bonded to a sp3 hybridized carbon which is attached to an aromatic
ring.
CH2X
(1°)
U Vinylic halides: In these, the halogen atom is bonded to a sp2 hybridized carbon atom of a C-C double bond.
X
U Aryl halides: In these compounds, the halogen atom is directly bonded to the sp2 hybridized carbon atom of an aromatic ring.
X
Important Facts
Halogen atoms are more electronegative than carbon, therefore, carbon-halogen bond of alkyl halide is
01 polarised.
02 The carbon-halogen bond length increases from C—F to C—I.
03 The order of reactivity of alcohols with a given haloacid is 3°>2°>1°.
04 Fluoro compounds are not prepared by electrophilic substitution due to high reactivity of fluorine.
Alkyl halides, when pure, are typically colorless, but bromides and iodides can develop color when
05 exposed to light due to photochemical reactions.
P
193 Haloalkanes and Haloarenes W
6
“ The chapter delves into the realm of
haloalkanes and haloarenes, exploring their
chemical properties, preparation methods, and
reactions. These compounds play a vital role
across various industrial and medical fields.
They are employed in the manufacture of
solvents, anaesthetics, and refrigerants, among
other applications. This chapter not only offers
a deep understanding of the structural nuances
and reaction mechanisms of these halogen-
containing compounds but also highlights their
practical applications, such as in the synthesis
of complex organic molecules and in medical
treatments, enriching our understanding
of their significance in everyday life and
technological advancements. ”
SYLLABUS &
WEIGHTAGE
Years
List of Concept Names 2022
2020 2021 2023 2024
(Term-1)
Nomenclature, Preparation And Physical Properties of
Haloalkanes and Haloarenes – 2 Q* 1 Q (1 M) –
(Nomenclature, nature of C–X bond, physical properties)
Exam not conducted
Chemical Properties of Haloalkanes 3Q 4Q 4Q
(Chemical properties, optical rotation, mechanism of 5 Q*
substitution reactions.) (1 M Each) (1 M Each) (1 M Each)
Chemical Properties of Haloarenes and Polyhalogen
Compounds
(Nature of C–X bond, substitution reactions (Directive 2Q 2Q
1 Q (1 M) 2 Q*
influence of halogen in monosubstituted compounds only), (1 M Each) (1 M Each)
Uses and environmental effects of - dichloromethane,
trichloromethane, tetrachloromethane, iodoform, freons, DDT)
* All questions were of MCQ type and carried equal marks.
, ● Cd+ – Xd– On the basis of no. of Compounds containing Compounds containing
Halogen Atoms sp3 C – X bond sp2 C – X bond
● Halogen atoms are more elec-
tronegative than carbon, there- ● Monohalogen compounds : – ● Alkyl Halides : R – X ● Vinylic Halides :
fore, carbon-halogen bond of CH3 – X X
● Allylic Halides:
alkyl halide is polarised. ● Dihalogen compounds : X
X
CH2 –X
CH2 –X CH2X ● Aryl Halides :
X X
● Polyhalogen compounds : ● Benzylic Halides:
CH2 – CH – CH2 CH2X
Nature of C – X H 3C
X X X
bond
Classification
CONCEPT MAP
Colour and Smell
● Alkyl halides are colourless when pure. However, bromides and
Haloalkanes and iodides develop colour when exposed to light.
Physical Properties
Haloarenes Solubility
● Very slightly soluble in water.
Chemical Reaction with Metals Melting and Boiling Points
● B.pt of chlorides, bromides and iodides are considerably higher than the
191
Reactions Grignard Reagent hydrocarbons of comparable molecular mass.
dry
R – X + Mg RMgX ● The B.pt of isomeric haloalkanes decrease with increase in branching.
ether
Methods of ● Para isomers have high M.pt than ortho and meta isomers.
Wurtz Reaction
Preparation dry Density
R – X + 2Na + X – R R – R + 2NaX
ether ● Density increases with increase in no. of carbon atoms, halogen atoms
and atomic mass of the halogen atoms.
From Alcohols From Hydrocarbons From diazonium Salt
ZnCl2 (a) By Free Radical Halogenation NaNO2 + HX N+2X–
R – OH + HCl R – Cl + H2O NH2
3R – OH + PX3 3R – X + H3PO3 Cl2,UV 273-278 K
CH3CH2CH2CH3 CH3CH2CH2CH2Cl +
R – OH + PCl5 R – Cl + POCl3 + HCl CH3CH2CHClCH3 Benzene
diazonium
R – OH + SOCl2 R – Cl + SO2 + HCl↑ (b) By Electrophilic Substitution halide
Sandmeyer’s Reaction
Halogen Exchange CH3 CH3 CH3
Fe/Dark N+2X– X
+ X2 + Cu2X2
To Access One
(a) Finkelstein reaction: X X
+ N2
Scan This QR Code
Shot Revision Video
dry acetone o-Halotoluene p-Halotoluene
Aryl Halide
R – X + NaI R – I + NaX
N+2X– I
KI
(b) Swart’s reaction: + N2
CH3Br + AgF/Hg2F2/CoF2/SbF3 CH3F + AgBr
Haloalkanes and Haloarenes
P
W
,P
W
Aryl halides are extremely less reactive 1. Nucleophilic Substitution Reactions 3. Reaction With Metals
towards Nu–Sub. reactions due to: Replacement by Hydroxyl Group:- Wurtz Fittig Reaction
1. Resonance Effect Cl OH Cl OH dry ether
X+ Na + R – X R + NaX
2. Difference in Hybridisation of carbon
atom in C – X Bond. (i) NaOH, 623K (i) NaOH, 443K Fittig Reaction
(ii) H+ (ii) H+ X
3. Instability of phenyl cation
4. Because of possible repulsion it is less NO2 NO2 dry ether
likely for Nu– to approach e– rich arenes 2 + 2Na + 2NaX
diphenyl
Haloarenes
Haloalkanes and Chemical Nucleophilic
Haloarenes Reactions Substitution Reactions
2. Electrophilic Substitution Reactions
(i) Halogenation
Cl Cl Cl
Cl Unimolecular Nucleophilic Substitution Bimolecular Nucleophilic Substitution
Anhyd. FeCl3 Reaction (SN2)
+ Cl2 + Reaction (SN1)
CH3 H
+ H
192
Cl STEP 1 OH– + H Cl OH Cl
(CH3)3CBr H3C CH3 + Br– H
1, 4-dichloro- 1, 2-dichloro-
benzene benzene H H
H3 C + STEP II Nu– substrate
(ii) Nitration (major) (minor) H3 C
CH3 + ŌH (CH3)3C – OH
Cl H
Cl Rate ∝ [Substrate] OH
Cl H + Cl–
conc. HNO3 NO2 Reactivity = 3° > 2° > 1° > CH3 Rate ∝ [Nu–] [substrate] H
+ Racemisation occurs Reactivity = 3° < 2° < 1° < CH3
H2SO4, D
(minor) Inversion in configuration occurs
NO2
(iii) Sulphonation (major)
Cl Cl
Elimination Reactions Polyhalogen Compounds
SO3H Dichloromethane
conc. H2SO4
Cl + ● Paint Remover
D
● Propellants in Aerosols
(minor) H
SO3H B–: Trichloromethane
(major) b a ● Solvent for Fats
(iv) Friedel Craft’s Reaction C C C=C + B – H + X–
Iodoform
Cl Cl Cl X ● Antiseptic
O
COCH3 Saytzeff Rule | Zaitsev Rule : Freons
Anhyd. AlCl3 In dehydrohalogenation, the preferred product
+ CH3 – C – Cl + ● For aerosol propellants, refrigeration and air
is that alkene which has the greater number conditioning purposes.
(minor) of alkyl groups attached to the doubly bonded
COCH3 carbon atom. DDT
(major) ● As insecticides
, NOMENCLATURE, PREPARATION AND PHYSICAL
1 PROPERTIES OF HALOALKANES AND HALOARENES
NCERT Definitions (Commonly asked in 1 mark)
U Haloalkanes: Alkanes that have halogen atoms attached to the sp3 hybridized carbon of an alkyl halide.
U Haloarenes: Aromatic hydrocarbons that have halogen atoms attached to the sp2 hybridized carbon of an aryl halide.
U Allylic halides: In these types of halides, the halogen atom is bonded to an sp3 hybridized carbon atom which is adjacent to carbon
carbon double bond.
X Allylic carbon
U Benzylic halides: In these compounds, the halogen atom is bonded to a sp3 hybridized carbon which is attached to an aromatic
ring.
CH2X
(1°)
U Vinylic halides: In these, the halogen atom is bonded to a sp2 hybridized carbon atom of a C-C double bond.
X
U Aryl halides: In these compounds, the halogen atom is directly bonded to the sp2 hybridized carbon atom of an aromatic ring.
X
Important Facts
Halogen atoms are more electronegative than carbon, therefore, carbon-halogen bond of alkyl halide is
01 polarised.
02 The carbon-halogen bond length increases from C—F to C—I.
03 The order of reactivity of alcohols with a given haloacid is 3°>2°>1°.
04 Fluoro compounds are not prepared by electrophilic substitution due to high reactivity of fluorine.
Alkyl halides, when pure, are typically colorless, but bromides and iodides can develop color when
05 exposed to light due to photochemical reactions.
P
193 Haloalkanes and Haloarenes W
