Organic Chemistry: Concepts and Applications - Headley Allan D. 2020

Heteroatomic Functional Groups and Organic Nomenclature
3.2 Nomenclature of Alcohols

Alcohols are named as alkanols in the IUPAC system of nomenclature. For the alkanes that are used to derive the root names for alcohols, the ane is changed to -anol (or the e of the alkane is changed to ol). In naming alkanols, the longest continuous chain that contains the ─OH functionality is identified and used as the root name for the alkanol. In numbering alkanols, start at the end closest to the OH functionality and use the number of the carbon to which the ─OH group is attached to specify the location of the functionality in the IUPAC name, as shown in the example below.

In naming alcohols that have branches, start the numbering from the end closest to the alcohol functionality and not at the branch as in the case in numbering alkanes. An example of the correct and incorrect method of numbering the longest chain of a branched alcohol is shown below.

Note that in the above incorrect example, even though the branch is in position 2 and the ─OH is in position 4, a branch does not take priority over the ─OH functionality. That is, the ─OH functionality must always get the lowest number and not the location of branching. In naming an alcohol, the position of the OH functionality must be specified by a number, and in the above example, the number 3 is used to specify the location of the OH functionality.

Problem 3.2

i. Give the IUPAC names for the following alcohols.

ii. Give the line-angle structures of the following molecules.

1. 2,2-Dimethyl-3-pentanol

2. 2,3,4-Trimethyl-2-hexanol

3.2.1 Nomenclature of Difunctional Alcohols

A source of confusion in the nomenclature of alkanols arises typically when the OH functionality is present in the same molecule that has another functionality, such as an alkene. The OH functionality is sometimes named as a hydroxy substituent if additional functional groups are present in the molecule, but typically the functionalities are combined as shown in the example below.

Note that in this case, the numbering system is based on the longest chain that contains both the alkene and OH functionalities. Also, note that the numbering is determined based on the alcohol functionality having, the lowest number. The alcohol functionality has priority over the alkene functionality.

Problem 3.3

i. Give the line-angle structure of 1-pentyn-3-ol.

ii. Give the IUPAC names for the compounds shown below.

3.2.2 Nomenclature of Cyclic Alcohols

In naming cyclic alcohols, the root name becomes cycloalkanol. In numbering cyclic alcohols, the carbon that has the ─OH functionality gets #1, and the numbering proceeds in the direction of the branches to give the lowest possible number combination, an example of naming a substituted cycloalkanol is shown below.

Problem 3.4

i. Give the IUPAC name of the molecule shown below.

ii. Give the structure of 2,3-dichloro-4-methylcyclobutanol

3.2.3 Nomenclature of Substituted Phenols

The structure of phenol was given earlier in the chapter, and substituted phenols are named such that phenol is the root name as shown in the examples below. Note that the carbon that has the OH group gets #1 and the numbering is similar to other cyclic structures in that the number combination of the name is the lowest.

If there are more than two different groups on the phenol ring, they are listed alphabetically.

Problem 3.5

i. Give the names for the following substituted phenols.

ii. Give the structures that correspond to the following molecules.

1. 2,4-Dibromophenol

2. 2,4,6-Trimethylphenol

3. 2-Bromo-4-chlorophenol