Dec 022012
 

Homologous series is the series of organic compounds containing same functional group and their adjacent members differ by -CH2 group. The members of homologous series have similar chemical properties but different physical properties.
For example:
CH3-OH
CH3-CH2-OH
CH3-CH2-CH2-OH
CH3-CH2-CH2-CH2-OH

Characteristics of Homologous Series

  1. They have same general formulae. For example, the general formula of alcohol is CnH2n+1OH, where n = Number of carbon atoms. By putting different values of n, such as 1, 2, 3, 4 etc., different members of homologous series can be obtained.
  2. They have same functional group and hence same chemical properties.
  3. They can be prepared by same general methods of preparation.
  4. They have different physical properties such as boiling point, melting point, molecular weight etc.

Cleavage of a bond (Fission of a bond)

  • Homolytic Cleavage: If the fission of a bond takes place in such a way that the electrons are distributed equally among the carbon atoms containing the bond, then this type of fission is called homolytic fission or cleavage. It takes place in the presence of sunlight and results into the formation of free radicals, which can be defined as the atom or group of atoms containing unpaired electrons.
    For example:homologous series
  • Heterolytic Cleavage: If the cleavage of bond takes place in such a way that electrons are distributed unequally among the atoms containing the bond, then such type of fission is called heterolytic fission. It takes in the presence of solvent and results into the formation of cations and anions.
    For example: