Alcohols

Alcohols are hydrocarbon compounds containing one or more hydroxyl group (O — H) attached to a saturated carbon atom.

Alcohol Homologous Series

The alcohols which only contain one hydroxyl group attached to a saturated carbon form a homologous series.

A hydrocarbon homologous series is a series of hydrocarbons which:

  • Have the same general formula
  • Differ by CH2 in molecular formulae from neighbouring compounds
  • Show a gradual variation in physical properties i.e. boiling and melting point
  • Have similar chemical properties

The general formula for the homologous series of alcohols is:

CnH(2n+1) –– OH

where n is the number of carbon atoms and OH represents the hydroxyl group.



 

Alcohols in the homologous series can be regarded as alkanes in which one hydrogen atom is replaced by a hydroxyl group. They are named by replacing the final “e” in the corresponding alkane by “ol”.

The table below shows the first four alcohols in the alcohol homologous series:

Name Number of Carbon atoms Molecular Formula CnH2n+1OH Structural Formula
Methanol 1 C1H2(1)+1OH = CH2+1OH = CH3OH
Ethanol 2 C2H2(2)+1OH = C2H4+1OH = C2H5OH
Propanol 3 C3H2(3)+1OH = C3H6+1OH = C3H7OH
Butanol 4 C4H2(4)+1OH = C4H8+1OH = C4H9OH