Question

What is a homologous series? Explain with an example.

[2 Mark]

Answer 1

A homologous series is a series of compounds with same functional group that differs by a $-C{H}_2$ unit.
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For example: methane, ethane, propane, butane, etc. are all part of the alkane homologous series. The general formula of this series is ${\text{C}}_{\text{n}}{\text{H}}_{\text{{2n+2}}}$.
Methane: ${\text{CH}}_4$
Ethane: ${\text{CH}}_3{\text{CH}}_3$
Propane: ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_3$
Butane: ${\text{CH}}_3{\text{­CH}}_2{\text{CH}}_2{\text{CH}}_3$
It can be noticed that there is a difference of ${\text{-CH}}_2$ unit between each successive compound.
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