Homologous Series Definition, Formula, Types and Characteristics – Organic Chemistry

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Organic compounds are classified into different series on the basis of functional groups. These series are called homologous series. Thus the study of organic compounds becomes easier.

Homologous Series:

Homo means “same ” and series means “sequence”

so

A series of organic compounds have the same functional group, same chemical properties but each member is different from the next member by a methylene group (-CH2) & physical properties are called homologous series.

What is meant by homologous series?

Homologous Series Definition:

              A series of compounds in which there is a constant difference of methylene (-CH2-) group between any two successive members of the family.

Each member of the homologous series is called a homolog.

Homologous series of alkane ,alkyne and alcohols

What are homologs?

In Organic chemistry, homologous series adjacent members differ by methylene (-CH2-) group. These individual members are called homologs.

General characteristics of Homologous Series:

  1. There is a constant difference in the methylene (-CH2-) group between any two successive members of a homologous series.
  2. All the members of a homologous series can be represented by a general formula e.g. general formulae for alkanes, alkenes, alkynes, alcohols, alkyl halides are CnH2n+2, CnH2n, CnH2n2, CnH2n+1OH, CnH2n+1X respectively.
  3. All the members of a homologous series have same functional group.
  4. All the members of a homologous series have same general chemical properties.
  5. There is a gradual change in physical properties in a homologous series from lower members to higher members.
  6. All the members of a homologous series can be prepared by same general methods of preparations.
  7. All families of organic compounds form a homologous series.

General Formula for alkane ,alkene & alkyne:

general formula for alkane ,alkene and alkyne
Homologous series Definition ,Formula ,Examples

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