Types of alcohols

There are three types of alcohol molecules. The type of alcohol is determined by the position of the hydroxyl functional group.

Primary alcohols

A primary alcohol is one in which the hydroxyl group (–OH) is attached to a carbon atom with at least two hydrogen atoms.

This will only occur when the hydroxyl group is at the end of the molecule chain.

Propan-1-ol has the structural formula of a carbon atom bonded to three hydrogen atoms, joined to a carbon with two hydrogens, which is joined to a carbon with two hydrogens and a hydroxyl group.

Propan-1-ol is a primary alcohol.

Secondary alcohols

A secondary alcohol is one in which the hydroxyl group (-OH) is attached to a carbon with only one hydrogen atom attached.

This can happen somewhere in the middle of a carbon chain.

Propan-2-ol has the structural formula of a carbon atom bonded to three hydrogen atoms, joined to a carbon with one hydrogen and a hydroxyl group, which is joined to a carbon with three hydrogens.

Propan-2-ol is a secondary alcohol.

Tertiary alcohols

A tertiary alcohol is one in which the hydroxyl group is attached to a carbon with no hydrogen atoms attached.

This will normally mean that the hydroxyl group is joined to the same carbon atom as a branch.

2-methylpropan-2-ol has structural formula of carbon atom bonded to three hydrogen atoms, joined to carbon with methyl group and hydroxyl group. Carbon atom is joined to carbon with three hydrogens.

2-methylpropan-2-ol is a tertiary alcohol.

Multiple hydroxyl groups

Alcohols can have more than one hydroxyl group:

  • Alcohols with two hydroxyl groups are called diols
  • Alcohols with three hydroxyl groups are called triols