Naming Alcohols

Classification of alcohols

Alcohols are classified as primary (1o), secondary (2o), or tertiary (3o) depending on the number of alkyl substituents attached to the carbon bonded to the O-H group.

methyl alcohol primary (1o) alcohol secondary (2o) alcohol tertiary (3o) alcohol

 

For example, ethanol and propan-1-ol are primary alcohol's.  Alcohols also have common names.  The common names are provided in parenthesis.

Examples of secondary alcohols include,

Tertiary alcohols have 3 carbons bonded to the same carbon the -O-H is bonded to.

Naming Alcohols using IUPAC rules

The IUPAC naming of alcohols is based on the name of the longest alkane/alkene (carbon) chain the hydroxyl group is bonded to.

  1. Find the longest carbon chain containing the hydroxyl group (OH).  This is the parent chain. Remove the final -e from the parent alkane chain name and add the suffix -ol.

  2. Number the parent chain such that the hydroxyl group gets the lowest possible number.  Older IUPAC rules originally placed the hydroxyl group number before the name of the parent chain.  However, the newer rules place the number before the -ol suffix.

  3. Number the substituents according to their position on the parent chain.  Then list the substituents in alphabetical order.  In the following example, the longest chain is 5 carbons in length, so it is a pentane parent chain.  The numbering started on the right, since this would give the -OH the lowest number. 

4. When naming a cyclic structure with a hydroxyl group, the -OH is assumed to be on the first carbon.

5. When multiple alcohols are present use di, tri, etc before the ol. Also, when a prefix is used the -e is not removed from the parent chain name ex. 2,3-hexanediol

6. When an alkene and alcohol are present in a molecule it is named as follows (location of the alkene)-(prefix for the parent chain + en)-(location of the hydroxyl)-ol

Naming Phenols

Phenols are named using the rules for aromatic compounds discussed here. Note that -phenol is used as the ending rather than -benzene.