Chapter – 10

Haloalkanes and Haloarenes

Haloalkanes and Haloarenes

Introduction to Haloalkanes and Haloarenes

On the basis of the number of halogen atoms                                               
Compounds containing sp3 C-X bond                                                             
Compounds having sp2 C-X bond

Nature of C-X Bond C-X Bond

Methods of preparation                                                                                     
From Alcohols                                                                                                               
From Hydrocarbons                                                                                               
Halogen Exchange

Physical Properties

Chemical Reactions                                                                     
Nucleophilic substitution reactions                                                               
Elimination reactions                                                                                               
Reaction with metals

Reactions of Haloarenes                                                                                     
Nucleophilic substitution                                                               
Electrophilic substitution reactions                                                                       
Reaction with metals

Polyhalogen Compounds                                                                   
Dichloromethane (Methylene chloride)                                         
Trichloromethane (Chloroform)                                                         
Triiodomethane (Iodoform)                                                     
Tetrachloromethane (Carbon tetrachloride)                             

Haloalkanes and Haloarenes

(1) Introduction:

The replacement of hydrogen atom(s) in a hydrocarbon, aliphatic or aromatic, by a halogen atom(s) results in the formation of alkyl halide (haloalkane) and aryl halide (haloarene), respectively.
These are compounds containing halogen atoms attached to an alkyl or aryl group. The general representation of haloalkanes is R-X and that of haloarenes is Ar-X [where X = F, Cl, Br, I].
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 a wide range of organic compounds.

(2) Classification:

Haloalkanes and haloarenes may be classified as follows:

On the Basis of Number of Halogen Atoms: Alkyl halides and aryl halides both are classified as mono-, di-, tri- or polyhalogen derivatives depending on the number of halogen atoms present in their structure.

Mono-halogen compounds contain only one halogen atom, dihalo-compounds contain 2 halogen atoms and poly-halogen compounds contain more than 2 halogen atoms.
C2H5X     ——    Mono-halogen Compound
XCH2 – CH2X       ——-     Di-halogen Compound
XCH2 – CHX – CH2X      ——-    Poly-halogen Compound

Haloalkanes and Haloarenes

Compounds Containing sp3 C-X Bond:
a). Alkyl Halides or Haloalkanes: Here the halogen atom is directly bonded to sp3 hybridized C atom of an alkyl group. They are further classified as primary, secondary, or tertiary according to the nature of carbon to which the halogen atom is attached. Their general formula may be:
Primary haloalkane: R-CH2-X,           Secondary haloalkane: R2CH-X
Tertiary haloalkane:    R3C-X

b). Allylic Halides: These are the compounds in which the halogen atom is bonded to sp3 hybridized carbon atom next to a C = C bond.  E.g.: CH2=CH-CH2X.

c). Benzylic Halides: These are the compounds in which the halogen atom is bonded to an sp3-hybridised carbon atom next to an aromatic ring. For example. C6H5-CH2-X.

Compounds having sp2 C-X bond: This class includes:
(a) Vinylic Halides: These are the compounds in which the halogen atom is bonded to a sp2-hybridised carbon atom of a carbon-carbon double bond (C = C).
E.g.: CH2=CH-X.
(b) Aryl halides: Here the halogen atom is directly bonded to sp2 hybridized carbon atom of an aromatic ring.  E.g.: C6H5-X.

Nomenclature: Common name of alkyl halides is obtained by adding –yl halide to the word root (i.e. word root + yl halide) and the IUPAC name is obtained by adding the prefix ‘halo’ to the name of the parent alkane (i.e. halo + alkane). Some examples are:                   

Haloalkanes Methods of Preparation

Haloalkanes and Haloarenes

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