Haloalkanes an Introduction

Introduction

Haloalkanes

The halogen derivatives of alkane are called haloalkanes. Or the organic compound containing halogen atom (X = -F, -Cl, -Br, -I) as functional group are called haloalkanes.

R-H + X ⟶ R-X + H

alkane           haloalkane

CH₃-H + Cl₂ ⟶ CH₃-Cl + HCl

methane                chloromethane

They are also called alkyl halides.

Haloalkanes are formed by the replacement of one or more hydrogen atom of alkane by same number of halogen atom and are bonded with carbon atom of alkane through strong covalent bond. They are represented by general molecular formula C_nH_2n+1X.

Nomenclature of haloalkanes

Prefix + word root + primary suffix

Side chain    number of                    nature of  

branches      C- atoms                        C- atoms

substituents

(-X=halo) (-F= fluoro, -Cl= Chloro, -Br= bromo, -I= iodo0

Classification of haloalkanes

A)   On the basis of nature of carbon atom

1.      Primary haloalkane (1˚)

The haloalkane in which the halogen containing carbon is further bonded to one carbon atom (one alkyl group) is called primary haloalkane.  

R-CH₂−X                                                                                               CH₃−CH₂−Cl

(1˚-Carbon)                                                                                         chloroethane

primary haloalkane                                                                         (ethyl chloride)

2.       Secondary haloalkane (2˚)

The haloalkane in which the halogen containing carbon is further bonded to two carbon atom (two alkyl group) is called secondary haloalkane.

3.      Tertiary haloalkane (3˚)

The haloalkane in which the halogen containing carbon is further bonded to three carbon atom (three alkyl group) is called tertiary haloalkane.

B)   On the basis of number of halogen atoms

1.      Mono-haloalkane

Haloalkane containing only one halogen atom.

CH₃-Cl                                             CH₃CH₂-Br

                    Chloromethane                         bromoethane   

2.      Di-haloalkane

Haloalkane containing two halogen atoms.

Cl-CH₂-CH₂-Cl                                     CH₃-CHCl₂

                     1,2-dichloroethane (vic.)           1,1-dichloroethane (gem.)

3.      Poly-haloalkane

Haloalkane containing three or more halogen atoms.

CHCl₃                                           CHI₃                                            CCl₄

chloroform                           iodoform                        carbon tetrachloride

Isomerism in haloalkanes                           

1.    Chain isomerism

Haloalkanes having same molecular formula but different number of carbon chain length are called chain isomers.

2.    Position isomerism

Haloalkanes having same molecular formula but different position of halogen atom on carbon chain are called position isomers.