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:
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|