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Haloalkanes and Haloarenes
IIT-JEE Chemistry Siddhivinayaka Educational Academy Rajendra Nagar Chowk Link Road Bilaspur Ph-07752- 237799/238799 Website : www.bajpaigroup.com. e-mail - info@bajpaigroup.com CHAPTER
23
LEARNINg OBJECTIvES
(i) Name haloalkanes and haloarenes according to the IUPAC system of nomenclature from their given structures. (ii) Describe the reactions involved in the preparation of haloalkanes and haloarenes and understand various reactions that they undergo.

(iii) Correlate the structures of haloalkanes and haloarenes with various types of reactions. (iv) Use stereochemistry as a tool for understanding the reaction mechanism. (v) Describe common polyhalogen compounds.

INTRODUCTION
The replacement of hydrogen atom(s) in a hydrocarbon, aliphatic or aromatic, by halogen atom(s) results in the formation of alkyl halide (haloalkane) and aryl halide (haloarene), respectively. 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 soil microorganisms is very effective for the treatment of typhoid fever.

The compounds containing more than one halogen atoms are commonly called as polyhaloalkanes, or polyhaloarenes depending upon the hydrocarbon residue in the molecule. Haloalkanes and haloarenes are important intermediates in synthetic organic chemistry due to, (i) the greater ease with which these derivatives can be prepared. (ii) their high reactivity. CLASSIfICATION

The compounds formed by replacement of one or more Hydrogen atoms from hydrocarbon molecule by corrersponding number of halogen atoms are called halogen derivatives or halides.
Hydrocarbon Halogen Derivative
On the basis of hydrocarbon part halides are classified as follows :
Halides Example
(a) Alkyl halides (Halogen derivatives of alkanes) CH3
CH2
Cl (Ethylchloride)
(b) Alkenyl halide (Halogen derivative of alkenes) CH2
=CH–Cl (Vinylchloride), CH2
= CH–CH2
–Cl (Allylchloride)
(c) Alkynyl halide (Halogen derivative of alkynes) CH≡C–CH2 –Cl (Propargylchloride)
(d) Aryl halide (Halogen atom is directly attached Chlorobenzene to carbon atom of aromatic nucleus)
Alkyl halides can be classified as methyl halide, primary alkyl halide, secondary alkyl halide (2°) and tertiary alkyl halide (3°), according to the number of other carbon atoms attached to the carbon bearing the halogen atom.

Methyl halide
X
H
H
H X
H
H
R X
R'
H
R X
R'
R"
R
Primary alkyl
halide (1°)
Secondary alkyl
halide (2°)
Tertiary alkyl
halide (3°)
R, R′ and R′′ may be same or different.
As we know that the alkyl halides contains halogen atom which is the functional group, which is responsible for the characteristic reactions viz. nucleophilic substitution and elimination reactions, of alkyl halides. So, it is functional group (X) which will decide the nature of the reaction (i.e. substitution and elimination) and not the alkyl group. The nature of alkyl group (i.e. 1°, 2°, 3°) will decide the mode (whether SN

2 or SN
1 and E
2
or E
1
).
HALOALkANES AND HALOARENES2
Haloalkanes and Haloarenes
IIT-JEE Chemistry Siddhivinayaka Educational Academy Rajendra Nagar Chowk Link Road Bilaspur Ph-07752- 237799/238799 Website : www.bajpaigroup.com. e-mail - info@bajpaigroup.com NOmENCLATURE :
The general formula of saturated mono substituted alkyl halide is Cn H2n+1
X, where X is a halogen atom. Alkyl halides are usually represented by R – X where R is an alkyl group. For example :
H3C
Br
H3C
CH3
Cl
H3C
H3C
CH3
I
1-bromopropane
1-chloro-2-methylpropane 1-iodo-2,2-dimethylpropane
Some examples of substituted alkyl and aryl...
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