HALOALKANES AND HALOARENES
SUBTHEME – CLASSIFICATION
CONCEPT- The replacement of hydrogen in
a hydrocarbon, aliphatic or aromatic ,by
halogen atoms result in the formation of
alkyl halide (haloalkane) and aryl
halide(haloarenes),respectively.
R-H -H/+X R-X
Ar-H
-H/+X
Ar-X
ON THE BASIS OF NUMBER
OF HALOGENS ATOMS
These may be classified as mono, di or
poly halogens (tri, tetra, etc).Compound
depending on whether they contain one
or two or more halogens atom in their
structure .For example.
C2H5X
CH2X
CH2X
CH2X
CH2X
X
X
CH2X
X
X
X
X
Monohaloarene
Dihaloarene
Trihaloarene
Monohalocompound may further be classified
according to the hybridization of the carbon
atom to which the halogens is bonded, as
discussed below
COMPOUND CONATANING SP3
C-X BOND (X=F,Cl,Br,I)
Alkyl halides or haloalkanes
In alkyl halides, the halogens atom is bonded
to an alkyl group(R) .They further form
a homologous series represented
by
CnH2n+1X.They are further classified as
primary ,secondary, or tertiary according to
this nature of carbon to which halogens are
attached.
H
R’
R’ C X
R” C X
H
H
(PRIMARY10)
R’
R’’ C X
R’’
(Secondary 20) ( teritary30)
ALKYL HALDIES
These are the compound in which the
halogens atom is bonded to an sp3hybridised
carbon atom next to carbon carbon doubled
bond (C=C) i.e. to an allylic carbon.
=
x
CH2X
Benzylic halides
These are the compound in which the
halogens atom is bonded to an sp3 carbon
atom next to an aromatic ring.
R
CH2 X
X
R’’
(10)
R’=CH3R’’=H (20)
R’=R’’=CH3(30)
COMPOUNDS CONTAINING sp3C X BOND
Vinylic halides
These are the compound in which the
halogens atom is bonded to an sp3hybridised
carbon atom of a carbon –carbon doubled
bond (C=C).
=
X
X
ARYL HAIDIES
These are the compound in which the
halogens atom is bonded to the sp3 hybridized
carbon atom of a aromatic ring .
X
Nomenclature
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 halide. Alkyl halide is named as halo
substituted hydrocarbons in the IUPAC system
of nomenclature. Haloarenes are the common
as well as IUPAC names of aryl halides. For
dihalogen derivates, the prefixes o,p,m are
used in common system but in IUPAC system,
the numerals 1,2;1,3 and 1,4 are used .
CH3CH2CH2Br
Common name: n-Propyl bromide
IUPAC name: 1-Bromopropane
H3-CH-CH3
Cl
Common name: Isopropyl chloride
IUPAC name: 2-chloropropane
H3C-CH-CH2Cl
CH3
Common name: Isobutyl chloride
IUPAC name: 1-chloro-2-methylpropane
Br
Common names: Bromobenzene
IUPAC name: Bromobenezene
Br
Br
Common name: m-Dibromobenzene
IUPAC name: 1, 3 –Dibromobenzene
Br
Br
Br
Common name: Tribromobenzene
IUPAC name: 1,3,5-Tribromobenzene
CH3
H3C-C-CH2-Cl
CH3
IUPAC name: 1-Chloro-2,2dimethylpropane
H3C-CH-CH3
Br
IUPAC name: 2-Bromopropane
The dihaloalkalanes having the same type of
halogen atoms are named as alkylidene or
alkylene dihalides.The dihalo-compounds
having the same type of halogen are further
classified as germinal halides (halogen atoms
are present on the same carbon atom) and
vicinal halides (halogen atoms are present on
the 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.
H3C-CHCl2
Common name: Ethylidene chloride (gemhalide)
IUPAC name: 1, 1-dichloroethane
H3C-CH2
Cl Cl
Common name: Ethylene dichloride (vicdihalide)
IUPAC name: 1, 2-dichloroethane
Nature of C-X Bond
Since halogen atoms are more electronegative
than carbon –halogen bond of alkyl halide is
polarized; the carbon atom bears a partial
negative charge.
C+-XSince the size of halogen atom increases as
we go down the group in the periodic table,
fluorine atom is the smallest and iodine
atom, the largest. Consequently the carbonhalogen bond length also increases from C-F
to C-I.
HOME ASSIGNMENT
Q1. Write the IUPAC name of the
following
(1) (CH3)2CHCH(Cl)CH3
(2) CH3CH2CH(CH3)CH(C2H5)Cl
Q2.Write the structure of the following
(1) 2-Chloro-3-methylpentane
(2) 2-Bromobutane
Class-XII B
Subject- Chemistry
Teacher sign
J.P SINHA (PGT)
PRINCIPAL