What is Homologous series? Explain with an example.

A homologous series is a series of organic compounds which belong to the same family (i.e. possess same functional group) and show similar chemical properties. The members of this series are called homologue and differ from each other by the number of CH2 units in the main carbon chain. Following are the characteristics of a homologous series

  • All homologues of a series have the same general formula e.g., all alkanes have the general formula Cn H2n + 2, alkyl halides have the general formula CnH(2n+1)X, alkenes have the general formula CnH2n etc.
  • Each consecutive member differs from the next by one carbon atom and two hydrogen atoms (-CH2 group).
  • The difference in the molecular mass between two consecutive homologues is 14 amu.
  • The physical properties of homologues show a regular gradation.
  • Homologues of a series have similar chemical properties.

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the series of hydrocarbons with a differece of CH2

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ex - methane ( CH4) , ethane (C2H6) .............

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the series of hydrocarbons having similar structure and similar properties where each successive compound differs by CH2 group

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