HOMOLOGOUS SERIES:

 HOMOLOGOUS SERIES:

"A series of organic compound in which each member is different from the next member by a methylene (-CH2-) group is called homologous series".

All the members that differ from each other by methylene group, are called homologues. Each class of organic compounds has its own homologous series which can be represented by a general formula. For example, alkanes (saturated hydrocarbons) can be represented by a series of compounds. It can be represented by a general formula CnH2n+2 where 'n' shows the number of carbon atoms in the corresponding alkane.

As it is clear from alkane homologous series that each member is different from the adjacent member by CH3. Similarly, this series can be expanded beyond C10 to higher alkanes. Similar homologous series can be developed for alkenes, alkynes, alcohols, ethers, amines, carboxylic acids, carbonyl compounds etc.

CHARACTERISTICS OF HOMOLOGOUS SERIES:

*Each class of organic compounds has its own homologous series having same  general formula.

*All the members of homologous series have similar chemical properties.

* They have same general methods of preparation similar structural features.

*They have same functional group.

*The physical properties like melting point, boiling point, densities etc, increase down the series due to increase in their molecular masses.

For Example lets see homology in alcohol.

CH3CH2OH                               Ehtyl alcohol

CH3CH2CH2OH                        Propyl alcohol

CH3CH2CH2CH2OH                 Butyl alcohol 

CH3CH2CH2CH2CH2OH          Pentyl Alcohol

CH3CH2CH2CH2CH2CH2OH  Hexyl alcohol

Consider another example:

CH3CH2Cl                               Ehtyl Chloride

CH3CH2CH2Cl                  Propyl Chloride

CH3CH2CH2CH2Cl              Butyl Chloride

CH3CH2CH2CH2CH2Cl        Pentyl Chloride

CH3CH2CH2CH2CH2CH2Cl  Hexyl Chloride