Homologous series

Question

What is homologous series?

can we put alkanes , alkenes , alkynes  in to same group or this is homologous series or not if yes then why if no then why not! 

 

Answer 1

No, Prasenjeet, we cannot lump alkanes, alkynes and alkenes into one "homologous" series.

 

The general formula for an alkane is C_nH_{2n + 2} (n ≥ 1) in which the repeating unit is -CH₂-

 

For 1-alkenes the general formula is C_nH_2n (n ≥ 2) for which the repeating unit is also -CH₂-, but notice how the general formula differs from that of alkanes.

 

As a final example consider 1-alkynes for which the general formula is C_nH_2n − 2 (n ≥ 2).

 

Compounds form a homologous series as long as they have the same general formula.  Thus methane, ethane, propane, butane etc. form one homologous series (the alkanes).  Alkenes and alkynes form their own series.