HOMOLOGOUS SERIES
 
 
 
 DEFINITION
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  A series of organic compounds that have similar structural features but differ from adjacent members by (-CH2) group is referred to as homologous series. Each member of homologous series is called homolog.
 
EXAMPLE
1. CH3-OH, CH3-CH2-OH, C3H7-OH are the members of a homologous series called "Alcohols".
2. CH3-COOH, CH3-CH2-COOH, C3H7-COOH are the members of homologous series called "Carboxylic     acids".
3. CH3-O-CH3, C2H5-O-CH3, C3H7-O-CH3 are the members of homologous series called "Ethers".
  CHARACTERISTICS OF A HOMOLOGOUS SERIES
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  1. STRUCTURAL FORMULA
All the members of a homologous series have same structural formula.
2. MOLECULAR FORMULA
Molecular formula of different members of a homologous series differs from previous and next member by CH2.
3. NATURE OF ELEMENT
All the members of series have same type of elements.
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4. FUNCTIONAL GROUP
All the members of homologous series contain same functional group.
5. GENERAL FORMULA
Members of a homologous series can be represented by a general formula.
 
FOR EXAMPLE:
ALKANE : CnH2n+1
ALKENE : CnH2n
ALKYNE : CnH2n-2
ALCOHOL : CnH2n+1 OH
ETHERS : CnH2nO
Where n = number of carbon atoms.
  6. MOLECULAR MASS
Molecular mass of any two consecutive members differ by 14 units
  7. CHEMICAL PROPERTIES
All the members of a homologous series have same chemical properties due to same functional group.
  8. METHODS OF PREPARATION
Generally all the members of a series can be prepared by using same method.
  9. PHYSICAL PROPERTIES
Physical properties of the members of a homologous series vary with the increase in atomic weight.
 
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