NCERT Textbook: Haloalkanes & Haloarenes | Chemistry Class 12 - NEET PDF Download

 Page 1


The replacement of hydrogen atom(s) in an aliphatic
or aromatic hydrocarbon by halogen atom(s) results
in the formation of alkyl halide (haloalkane) and aryl
halide (haloarene), respectively. Haloalkanes contain
halogen atom(s) attached to the sp
3
 hybridised carbon
atom of an alkyl group whereas haloarenes contain
halogen atom(s) attached to sp
2
 hybridised carbon
atom(s) of an aryl group. Many halogen containing
organic compounds occur in nature and some of
these are clinically useful. These classes of compounds
find wide applications in industry as well as in day-
to-day life. They are used as solvents for relatively
non-polar compounds and as starting materials for
the synthesis of wide range of organic compounds.
Chlorine containing antibiotic, chloramphenicol,
produced by microorganisms is very effective for the
treatment of typhoid fever. Our body produces iodine
containing hormone, thyroxine, the deficiency of which
causes a disease called goiter. Synthetic halogen
compounds, viz. chloroquine is used for the treatment
of malaria; halothane is used as an anaesthetic
during surgery. Certain fully fluorinated compounds
are being considered as potential blood substitutes
in surgery.
In this Unit, you will study the important methods
of preparation, physical and chemical properties and
uses of organohalogen compounds.
After studying this Unit, you 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 compounds;
· highlight the environmental effects
of polyhalogen compounds.
Objectives
6
Unit Unit Unit Unit Unit
6
Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and
Haloar Haloar Haloar Haloar Haloarenes enes enes enes enes
Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and
Haloar Haloar Haloar Haloar Haloarenes enes enes enes enes
Halogenated compounds persist in the environment due to their
resistance to breakdown by soil bacteria.
Reprint 2024-25
Page 2


The replacement of hydrogen atom(s) in an aliphatic
or aromatic hydrocarbon by halogen atom(s) results
in the formation of alkyl halide (haloalkane) and aryl
halide (haloarene), respectively. Haloalkanes contain
halogen atom(s) attached to the sp
3
 hybridised carbon
atom of an alkyl group whereas haloarenes contain
halogen atom(s) attached to sp
2
 hybridised carbon
atom(s) of an aryl group. Many halogen containing
organic compounds occur in nature and some of
these are clinically useful. These classes of compounds
find wide applications in industry as well as in day-
to-day life. They are used as solvents for relatively
non-polar compounds and as starting materials for
the synthesis of wide range of organic compounds.
Chlorine containing antibiotic, chloramphenicol,
produced by microorganisms is very effective for the
treatment of typhoid fever. Our body produces iodine
containing hormone, thyroxine, the deficiency of which
causes a disease called goiter. Synthetic halogen
compounds, viz. chloroquine is used for the treatment
of malaria; halothane is used as an anaesthetic
during surgery. Certain fully fluorinated compounds
are being considered as potential blood substitutes
in surgery.
In this Unit, you will study the important methods
of preparation, physical and chemical properties and
uses of organohalogen compounds.
After studying this Unit, you 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 compounds;
· highlight the environmental effects
of polyhalogen compounds.
Objectives
6
Unit Unit Unit Unit Unit
6
Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and
Haloar Haloar Haloar Haloar Haloarenes enes enes enes enes
Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and
Haloar Haloar Haloar Haloar Haloarenes enes enes enes enes
Halogenated compounds persist in the environment due to their
resistance to breakdown by soil bacteria.
Reprint 2024-25
160 Chemistry
Haloalkanes and haloarenes may be classified as follows:
These may be classified as mono, di, or polyhalogen (tri-,tetra-, etc.)
compounds depending on whether they contain one, two or more halogen
atoms in their structures. For example,
Monohalocompounds may further be classified according to the
hybridisation of the carbon atom to which the halogen is bonded, as
discussed below.
This class includes
(a) Alkyl halides or haloalkanes (R—X)
In alkyl halides, the halogen atom is bonded to an alkyl group (R).
They form a homologous series represented by C
n
H
2n+1
X. They are
further classified as primary, secondary or tertiary according to the
nature of carbon to which halogen is attached. If halogen is attached to
a primary carbon atom in an alkyl halide, the alkyl halide is called
primary alkyl halide or 1° alkyl halide. Similarly, if halogen is attached
to secondary or tertiary carbon atom, the alkyl halide is called
secondary alkyl halide (2°) and tertiary (3°) alkyl halide, respectively.
(b) Allylic halides
These are the compounds in which the halogen atom is bonded to an
sp
3
-hybridised carbon atom adjacent to carbon-carbon double bond
(C=C) i.e. to an allylic carbon.
(c) Benzylic halides
These are the compounds in which the halogen atom is bonded to an
sp
3
-hybridised carbon atom attached to an aromatic ring.
6.1 6.1 6.1 6.1 6.1 Classification Classification Classification Classification Classification
6.1.1 On the
Basis of
Number of
Halogen
Atoms
6.1.2 Compounds
Containing
sp
3 
C—X
Bond (X= F,
Cl, Br, I)
Allylic carbon
Allylic carbon
Reprint 2024-25
Page 3


The replacement of hydrogen atom(s) in an aliphatic
or aromatic hydrocarbon by halogen atom(s) results
in the formation of alkyl halide (haloalkane) and aryl
halide (haloarene), respectively. Haloalkanes contain
halogen atom(s) attached to the sp
3
 hybridised carbon
atom of an alkyl group whereas haloarenes contain
halogen atom(s) attached to sp
2
 hybridised carbon
atom(s) of an aryl group. Many halogen containing
organic compounds occur in nature and some of
these are clinically useful. These classes of compounds
find wide applications in industry as well as in day-
to-day life. They are used as solvents for relatively
non-polar compounds and as starting materials for
the synthesis of wide range of organic compounds.
Chlorine containing antibiotic, chloramphenicol,
produced by microorganisms is very effective for the
treatment of typhoid fever. Our body produces iodine
containing hormone, thyroxine, the deficiency of which
causes a disease called goiter. Synthetic halogen
compounds, viz. chloroquine is used for the treatment
of malaria; halothane is used as an anaesthetic
during surgery. Certain fully fluorinated compounds
are being considered as potential blood substitutes
in surgery.
In this Unit, you will study the important methods
of preparation, physical and chemical properties and
uses of organohalogen compounds.
After studying this Unit, you 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 compounds;
· highlight the environmental effects
of polyhalogen compounds.
Objectives
6
Unit Unit Unit Unit Unit
6
Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and
Haloar Haloar Haloar Haloar Haloarenes enes enes enes enes
Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and
Haloar Haloar Haloar Haloar Haloarenes enes enes enes enes
Halogenated compounds persist in the environment due to their
resistance to breakdown by soil bacteria.
Reprint 2024-25
160 Chemistry
Haloalkanes and haloarenes may be classified as follows:
These may be classified as mono, di, or polyhalogen (tri-,tetra-, etc.)
compounds depending on whether they contain one, two or more halogen
atoms in their structures. For example,
Monohalocompounds may further be classified according to the
hybridisation of the carbon atom to which the halogen is bonded, as
discussed below.
This class includes
(a) Alkyl halides or haloalkanes (R—X)
In alkyl halides, the halogen atom is bonded to an alkyl group (R).
They form a homologous series represented by C
n
H
2n+1
X. They are
further classified as primary, secondary or tertiary according to the
nature of carbon to which halogen is attached. If halogen is attached to
a primary carbon atom in an alkyl halide, the alkyl halide is called
primary alkyl halide or 1° alkyl halide. Similarly, if halogen is attached
to secondary or tertiary carbon atom, the alkyl halide is called
secondary alkyl halide (2°) and tertiary (3°) alkyl halide, respectively.
(b) Allylic halides
These are the compounds in which the halogen atom is bonded to an
sp
3
-hybridised carbon atom adjacent to carbon-carbon double bond
(C=C) i.e. to an allylic carbon.
(c) Benzylic halides
These are the compounds in which the halogen atom is bonded to an
sp
3
-hybridised carbon atom attached to an aromatic ring.
6.1 6.1 6.1 6.1 6.1 Classification Classification Classification Classification Classification
6.1.1 On the
Basis of
Number of
Halogen
Atoms
6.1.2 Compounds
Containing
sp
3 
C—X
Bond (X= F,
Cl, Br, I)
Allylic carbon
Allylic carbon
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161 Haloalkanes and Haloarenes
This class includes:
(a) Vinylic halides
These are the compounds in which the halogen atom is bonded to
a sp
2
-hybridised carbon atom of a carbon-carbon double bond
(C = C).
(b) Aryl halides
These are the compounds in which the halogen atom is directly
bonded to the sp
2
-hybridised carbon atom of an aromatic ring.
Having learnt the classification of halogenated compounds, let us now learn
how these are named. The common names of alkyl halides are derived by
naming the alkyl group followed by the name of halide. In the IUPAC system
of nomenclature, alkyl halides are named as halosubstituted hydrocarbons.
For mono halogen substituted derivatives of benzene, common and IUPAC
names are the same. For dihalogen derivatives, the  prefixes o-, m-, p- are
used in common system but in IUPAC system, as you have learnt in Class
XI, the numerals 1,2; 1,3 and 1,4 are used.
6.1.3 Compounds
Containing
sp
2 
C—X
Bond
The dihaloalkanes having the same type of halogen atoms are named
as alkylidene or alkylene dihalides. The dihalo-compounds having both
the halogen atoms are further classified as geminal halides or gem-dihalides
when both the halogen atoms are present on the same carbon atom of the
6.2 Nomenclature 6.2 Nomenclature 6.2 Nomenclature 6.2 Nomenclature 6.2 Nomenclature
Reprint 2024-25
Page 4


The replacement of hydrogen atom(s) in an aliphatic
or aromatic hydrocarbon by halogen atom(s) results
in the formation of alkyl halide (haloalkane) and aryl
halide (haloarene), respectively. Haloalkanes contain
halogen atom(s) attached to the sp
3
 hybridised carbon
atom of an alkyl group whereas haloarenes contain
halogen atom(s) attached to sp
2
 hybridised carbon
atom(s) of an aryl group. Many halogen containing
organic compounds occur in nature and some of
these are clinically useful. These classes of compounds
find wide applications in industry as well as in day-
to-day life. They are used as solvents for relatively
non-polar compounds and as starting materials for
the synthesis of wide range of organic compounds.
Chlorine containing antibiotic, chloramphenicol,
produced by microorganisms is very effective for the
treatment of typhoid fever. Our body produces iodine
containing hormone, thyroxine, the deficiency of which
causes a disease called goiter. Synthetic halogen
compounds, viz. chloroquine is used for the treatment
of malaria; halothane is used as an anaesthetic
during surgery. Certain fully fluorinated compounds
are being considered as potential blood substitutes
in surgery.
In this Unit, you will study the important methods
of preparation, physical and chemical properties and
uses of organohalogen compounds.
After studying this Unit, you 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 compounds;
· highlight the environmental effects
of polyhalogen compounds.
Objectives
6
Unit Unit Unit Unit Unit
6
Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and
Haloar Haloar Haloar Haloar Haloarenes enes enes enes enes
Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and
Haloar Haloar Haloar Haloar Haloarenes enes enes enes enes
Halogenated compounds persist in the environment due to their
resistance to breakdown by soil bacteria.
Reprint 2024-25
160 Chemistry
Haloalkanes and haloarenes may be classified as follows:
These may be classified as mono, di, or polyhalogen (tri-,tetra-, etc.)
compounds depending on whether they contain one, two or more halogen
atoms in their structures. For example,
Monohalocompounds may further be classified according to the
hybridisation of the carbon atom to which the halogen is bonded, as
discussed below.
This class includes
(a) Alkyl halides or haloalkanes (R—X)
In alkyl halides, the halogen atom is bonded to an alkyl group (R).
They form a homologous series represented by C
n
H
2n+1
X. They are
further classified as primary, secondary or tertiary according to the
nature of carbon to which halogen is attached. If halogen is attached to
a primary carbon atom in an alkyl halide, the alkyl halide is called
primary alkyl halide or 1° alkyl halide. Similarly, if halogen is attached
to secondary or tertiary carbon atom, the alkyl halide is called
secondary alkyl halide (2°) and tertiary (3°) alkyl halide, respectively.
(b) Allylic halides
These are the compounds in which the halogen atom is bonded to an
sp
3
-hybridised carbon atom adjacent to carbon-carbon double bond
(C=C) i.e. to an allylic carbon.
(c) Benzylic halides
These are the compounds in which the halogen atom is bonded to an
sp
3
-hybridised carbon atom attached to an aromatic ring.
6.1 6.1 6.1 6.1 6.1 Classification Classification Classification Classification Classification
6.1.1 On the
Basis of
Number of
Halogen
Atoms
6.1.2 Compounds
Containing
sp
3 
C—X
Bond (X= F,
Cl, Br, I)
Allylic carbon
Allylic carbon
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161 Haloalkanes and Haloarenes
This class includes:
(a) Vinylic halides
These are the compounds in which the halogen atom is bonded to
a sp
2
-hybridised carbon atom of a carbon-carbon double bond
(C = C).
(b) Aryl halides
These are the compounds in which the halogen atom is directly
bonded to the sp
2
-hybridised carbon atom of an aromatic ring.
Having learnt the classification of halogenated compounds, let us now learn
how these are named. The common names of alkyl halides are derived by
naming the alkyl group followed by the name of halide. In the IUPAC system
of nomenclature, alkyl halides are named as halosubstituted hydrocarbons.
For mono halogen substituted derivatives of benzene, common and IUPAC
names are the same. For dihalogen derivatives, the  prefixes o-, m-, p- are
used in common system but in IUPAC system, as you have learnt in Class
XI, the numerals 1,2; 1,3 and 1,4 are used.
6.1.3 Compounds
Containing
sp
2 
C—X
Bond
The dihaloalkanes having the same type of halogen atoms are named
as alkylidene or alkylene dihalides. The dihalo-compounds having both
the halogen atoms are further classified as geminal halides or gem-dihalides
when both the halogen atoms are present on the same carbon atom of the
6.2 Nomenclature 6.2 Nomenclature 6.2 Nomenclature 6.2 Nomenclature 6.2 Nomenclature
Reprint 2024-25
162 Chemistry
chain and vicinal halides or vic-dihalides when halogen atoms are present
on adjacent carbon atoms. In common name system, gem-dihalides are
named as alkylidene halides and vic-dihalides are named as alkylene
dihalides. In IUPAC system, they are named as dihaloalkanes.
Structure Common name IUPAC name
CH
3
CH
2
CH(Cl)CH
3
sec-Butyl chloride 2-Chlorobutane
(CH
3
)
3
CCH
2
Br neo-Pentyl bromide 1-Bromo-2,2-dimethylpropane
(CH
3
)
3
CBr tert-Butyl bromide 2-Bromo-2-methylpropane
CH
2 
= CHCl Vinyl chloride Chloroethene
CH
2 
= CHCH
2
Br Allyl bromide 3-Bromopropene
CH
2
Cl
2
Methylene chloride Dichloromethane
CHCl
3
Chloroform Trichloromethane
CHBr
3
Bromoform Tribromomethane
CCl
4
Carbon tetrachloride Tetrachloromethane
CH
3
CH
2
CH
2
F n-Propyl fluoride 1-Fluoropropane
o-Chlorotoluene 1-Chloro-2-methylbenzene
or
2-Chlorotoluene
Benzyl chloride Chlorophenylmethane
Table 6.1: Common and IUPAC Names of some Halides
Example 6.1 Example 6.1 Example 6.1 Example 6.1 Example 6.1
Solution Solution Solution Solution Solution
Draw the structures of all the eight structural isomers that have the
molecular formula C
5
H
11
Br. Name each isomer according to IUPAC system
and classify them as primary, secondary or tertiary bromide.
CH
3
CH
2
CH
2
CH
2
CH
2
Br 1-Bromopentane (1
o
)
CH
3
CH
2
CH
2
CH(Br)CH
3
2-Bromopentane(2
o
)
CH
3
CH
2
CH(Br)CH
2
CH
3
3-Bromopentane (2
o
)
(CH
3
)
2
CHCH
2
CH
2
Br 1-Bromo-3-methylbutane (1
o
)
Some common examples of halocompounds are mentioned in Table 6.1.
Reprint 2024-25
Page 5


The replacement of hydrogen atom(s) in an aliphatic
or aromatic hydrocarbon by halogen atom(s) results
in the formation of alkyl halide (haloalkane) and aryl
halide (haloarene), respectively. Haloalkanes contain
halogen atom(s) attached to the sp
3
 hybridised carbon
atom of an alkyl group whereas haloarenes contain
halogen atom(s) attached to sp
2
 hybridised carbon
atom(s) of an aryl group. Many halogen containing
organic compounds occur in nature and some of
these are clinically useful. These classes of compounds
find wide applications in industry as well as in day-
to-day life. They are used as solvents for relatively
non-polar compounds and as starting materials for
the synthesis of wide range of organic compounds.
Chlorine containing antibiotic, chloramphenicol,
produced by microorganisms is very effective for the
treatment of typhoid fever. Our body produces iodine
containing hormone, thyroxine, the deficiency of which
causes a disease called goiter. Synthetic halogen
compounds, viz. chloroquine is used for the treatment
of malaria; halothane is used as an anaesthetic
during surgery. Certain fully fluorinated compounds
are being considered as potential blood substitutes
in surgery.
In this Unit, you will study the important methods
of preparation, physical and chemical properties and
uses of organohalogen compounds.
After studying this Unit, you 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 compounds;
· highlight the environmental effects
of polyhalogen compounds.
Objectives
6
Unit Unit Unit Unit Unit
6
Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and
Haloar Haloar Haloar Haloar Haloarenes enes enes enes enes
Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and Haloalkanes and
Haloar Haloar Haloar Haloar Haloarenes enes enes enes enes
Halogenated compounds persist in the environment due to their
resistance to breakdown by soil bacteria.
Reprint 2024-25
160 Chemistry
Haloalkanes and haloarenes may be classified as follows:
These may be classified as mono, di, or polyhalogen (tri-,tetra-, etc.)
compounds depending on whether they contain one, two or more halogen
atoms in their structures. For example,
Monohalocompounds may further be classified according to the
hybridisation of the carbon atom to which the halogen is bonded, as
discussed below.
This class includes
(a) Alkyl halides or haloalkanes (R—X)
In alkyl halides, the halogen atom is bonded to an alkyl group (R).
They form a homologous series represented by C
n
H
2n+1
X. They are
further classified as primary, secondary or tertiary according to the
nature of carbon to which halogen is attached. If halogen is attached to
a primary carbon atom in an alkyl halide, the alkyl halide is called
primary alkyl halide or 1° alkyl halide. Similarly, if halogen is attached
to secondary or tertiary carbon atom, the alkyl halide is called
secondary alkyl halide (2°) and tertiary (3°) alkyl halide, respectively.
(b) Allylic halides
These are the compounds in which the halogen atom is bonded to an
sp
3
-hybridised carbon atom adjacent to carbon-carbon double bond
(C=C) i.e. to an allylic carbon.
(c) Benzylic halides
These are the compounds in which the halogen atom is bonded to an
sp
3
-hybridised carbon atom attached to an aromatic ring.
6.1 6.1 6.1 6.1 6.1 Classification Classification Classification Classification Classification
6.1.1 On the
Basis of
Number of
Halogen
Atoms
6.1.2 Compounds
Containing
sp
3 
C—X
Bond (X= F,
Cl, Br, I)
Allylic carbon
Allylic carbon
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161 Haloalkanes and Haloarenes
This class includes:
(a) Vinylic halides
These are the compounds in which the halogen atom is bonded to
a sp
2
-hybridised carbon atom of a carbon-carbon double bond
(C = C).
(b) Aryl halides
These are the compounds in which the halogen atom is directly
bonded to the sp
2
-hybridised carbon atom of an aromatic ring.
Having learnt the classification of halogenated compounds, let us now learn
how these are named. The common names of alkyl halides are derived by
naming the alkyl group followed by the name of halide. In the IUPAC system
of nomenclature, alkyl halides are named as halosubstituted hydrocarbons.
For mono halogen substituted derivatives of benzene, common and IUPAC
names are the same. For dihalogen derivatives, the  prefixes o-, m-, p- are
used in common system but in IUPAC system, as you have learnt in Class
XI, the numerals 1,2; 1,3 and 1,4 are used.
6.1.3 Compounds
Containing
sp
2 
C—X
Bond
The dihaloalkanes having the same type of halogen atoms are named
as alkylidene or alkylene dihalides. The dihalo-compounds having both
the halogen atoms are further classified as geminal halides or gem-dihalides
when both the halogen atoms are present on the same carbon atom of the
6.2 Nomenclature 6.2 Nomenclature 6.2 Nomenclature 6.2 Nomenclature 6.2 Nomenclature
Reprint 2024-25
162 Chemistry
chain and vicinal halides or vic-dihalides when halogen atoms are present
on adjacent carbon atoms. In common name system, gem-dihalides are
named as alkylidene halides and vic-dihalides are named as alkylene
dihalides. In IUPAC system, they are named as dihaloalkanes.
Structure Common name IUPAC name
CH
3
CH
2
CH(Cl)CH
3
sec-Butyl chloride 2-Chlorobutane
(CH
3
)
3
CCH
2
Br neo-Pentyl bromide 1-Bromo-2,2-dimethylpropane
(CH
3
)
3
CBr tert-Butyl bromide 2-Bromo-2-methylpropane
CH
2 
= CHCl Vinyl chloride Chloroethene
CH
2 
= CHCH
2
Br Allyl bromide 3-Bromopropene
CH
2
Cl
2
Methylene chloride Dichloromethane
CHCl
3
Chloroform Trichloromethane
CHBr
3
Bromoform Tribromomethane
CCl
4
Carbon tetrachloride Tetrachloromethane
CH
3
CH
2
CH
2
F n-Propyl fluoride 1-Fluoropropane
o-Chlorotoluene 1-Chloro-2-methylbenzene
or
2-Chlorotoluene
Benzyl chloride Chlorophenylmethane
Table 6.1: Common and IUPAC Names of some Halides
Example 6.1 Example 6.1 Example 6.1 Example 6.1 Example 6.1
Solution Solution Solution Solution Solution
Draw the structures of all the eight structural isomers that have the
molecular formula C
5
H
11
Br. Name each isomer according to IUPAC system
and classify them as primary, secondary or tertiary bromide.
CH
3
CH
2
CH
2
CH
2
CH
2
Br 1-Bromopentane (1
o
)
CH
3
CH
2
CH
2
CH(Br)CH
3
2-Bromopentane(2
o
)
CH
3
CH
2
CH(Br)CH
2
CH
3
3-Bromopentane (2
o
)
(CH
3
)
2
CHCH
2
CH
2
Br 1-Bromo-3-methylbutane (1
o
)
Some common examples of halocompounds are mentioned in Table 6.1.
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163 Haloalkanes and Haloarenes
Intext Question Intext Question Intext Question Intext Question Intext Question
6.1 Write structures of the following compounds:
(i) 2-Chloro-3-methylpentane
(ii) 1-Chloro-4-ethylcyclohexane
(iii) 4-tert. Butyl-3-iodoheptane
(iv) 1,4-Dibromobut-2-ene
(v) 1-Bromo-4-sec. butyl-2-methylbenzene.
Halogen atoms are more electronegative than carbon, therefore,
carbon-halogen bond of alkyl halide is polarised; the carbon atom bears
a partial positive charge whereas the halogen atom bears a partial
negative charge.
  As we go down the group in the periodic table, the size of halogen
atom increases. Fluorine atom is the smallest and iodine atom is the
largest. Consequently the carbon-halogen bond length also increases
from C—F to C—I. Some typical bond lengths, bond enthalpies and
dipole moments are given in Table 6.2.
Alkyl halides are best prepared from alcohols, which are easily accessible.
6.3 6.3 6.3 6.3 6.3 Nature of Nature of Nature of Nature of Nature of
C-X Bond C-X Bond C-X Bond C-X Bond C-X Bond
(CH
3
)
2
CHCHBrCH
3
2-Bromo-3-methylbutane(2
o
)
(CH
3
)
2
CBrCH
2
CH
3
2-Bromo-2-methylbutane (3
o
)
CH
3
CH
2
CH(CH
3
)CH
2
Br 1-Bromo-2-methylbutane(1
o
)
(CH
3
)
3
CCH
2
Br 1-Bromo-2,2-dimethylpropane (1
o
)
Write IUPAC names of the following:
(i) 4-Bromopent-2-ene (ii) 3-Bromo-2-methylbut-1-ene
(iii) 4-Bromo-3-methylpent-2-ene (iv) 1-Bromo-2-methylbut-2-ene
(v) 1-Bromobut-2-ene (vi) 3-Bromo-2-methylpropene
Example 6.2 Example 6.2 Example 6.2 Example 6.2 Example 6.2
Solution Solution Solution Solution Solution
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