NEET Chemistry Organic Compounds Containing Halogens

SYNOPSIS

The halogen derivative of hydrocarbons are called as halogenated hydrocarbons. The general formula of monohalogenated hydrocarbons is R-X. (X = F, Cl, Br, I and R= alkyl, aryl etc.)

1. Haloalkanes (R-X):
   
   
   • Classification:
     
   • Preparation:
     

   • General Characteristics:

     Bond energy order	C-F > C-Cl > C-Br > C-I
     Boiling point order	R-I > R-Br > R-Cl >R-F
     Density order	R-I > R-Br > R-Cl
     Dipole moment order	CH3Cl > CH3F > CH3Br > CH3I
     Stability order	R-F> R-Cl> R-Br>R-I

   • Chemical Characteristics:

   1. Nucleophilic substitution reactions
      There are four types of substitution reactions, their characteristics are given below:
      
      

      Type	SN1	SN2	SNi	SNAr
      Molecularity	Unimolecular	Bimolecular	Unimolecular	Bimolecular
      Order	Two-Step	One-step	One-step	Two-Step
      Medium	Acidic	Basic	Acidic	Basic
      Intermediate	Carbocation	No intermediate	No intermediate	Carbanion
      Orientation of product	Racemisation	Inversion	Retention	−

   2. Wittigs’ reactions:
      The formation of alkene by the action of ylide on carbonyl compounds is known as wittigs’ reaction.
      
      

   3. Friedal Craft reaction:
      
      
      
      

2. Haloarenes (Ar-X):
   Preparation:
   
   1. From aromatic hydrocarbons:
      
      
   2. From diazonium salt:
      
      
      
      Chemical Reactions of Benzene:
      
      
      
      
      
      
      
      
      
      Friedel-Craft’s alkylation
      
      
      
      

      Nucleophilic Aromatic Substitution:
      In this type of substitution reactions nucleophile attacked to the carbon of benzene ring having substituent. This reaction proceeds via an intermediate σ-complex, the benzenonium carbanion.
      
      e.g.,