Alcohols

Alcohol molecules all contain the hydroxyl (-OH) functional group. They are a homologous series and have the general formula CnH2n+1OH. Their names all end in -ol.

The rules for naming an alcohol are:

  1. Find the longest carbon chain and name it.
  2. Number the carbon atoms in the chain so that the functional group (in this case, the hydroxyl group) has the lowest possible number.
  3. Identify any branches joined onto the main chain and name them.
  4. Identify each branch by a number indicating its position. If more than one branch is present then a prefix must be used.

This simple alcohol molecule is called butan-2-ol.

The structural formula for butan-2-ol.

The names, molecular and structural formulae of some straight chain alcohols are shown in the table below.

Alchol table

When naming branched chain alcohols, be careful to number the longest possible carbon chain first.

C joined to 3 Hs linked to C with H and ethyl group. C joined to C with two H and hydroxyl group. Hydroxyl group labelled ‘functional group’.  Structure is 2-methylbutan-1-ol not 2-ethylpropan-1-ol.

When writing the name, you follow the convention of using commas between numbers and dashes between numbers and words.