Phenols Nomenclcature

IUPAC nomenclature refers to the systematic approach taken for the nomenclature of organic compounds as per the recommendation of the International Union of Pure and Applied Chemistry (often abbreviated to IUPAC). Phenol constitutes a major part of organic chemistry. They are considered as a class of chemical compounds which are bonded with the hydroxyl group and are attached to the carbon atom of the aromatic ring. Phenol has a hydroxyl group that is always bonded with a benzene ring and is known as an aromatic hydrocarbon group. Phenol is also referred to as phenolic, benzenol, or carbolic acids. 

Naming Phenols

Phenol consists of two parts: one aryl group and one hydroxyl group. So based on the number of aryl groups attached, phenols can be further sub categorized as mono-, di-, tri-, or polyhydric phenols. The IUPAC name for phenol is monohydroxybenzene or C6H5OH. 

Rules of Nomenclature

Before progressing further nomenclature of phenols, let us revise some fundamental rules of IUPAC nomenclature in general. 

According to the guidelines of IUPAC, the following rules are necessary to follow when practicing nomenclature:

  • The longest chain rule: As per this rule, parent hydrocarbon should be identified and labeled accordingly

  • The lowest set of locants: This rule implies the numbering of the carbon atoms that belong to the parent hydrocarbons.

  • Multiple instances of the same substituent: This rule refers to the usage of prefixes such as di-, tri-, mono- or poly.

  • The naming of different substituents: Alphabetical order must be followed for different substituents in one compound.

  • The naming of different substituents that are present in the same position: As per this rule, ascending alphabetical order is followed to name the compounds.

  • Naming complex substituents: Complex substituents must be named as alkyl groups which will be written in brackets.

Nomenclature of Phenols

There are certain guidelines drawn by IUPAC that are also followed while naming phenol as per the IUPAC nomenclature.

  1. IUPAC name of phenol is benzenol. When a molecule of a hydroxyl group, i.e OH group, is attached to a benzene ring, it forms the structure of phenol. 

  1. When there is more than one hydroxyl group, then the benzene ring is labeled as di-, tri- or poly prefixes which denote the number of OH groups attached to the rings. 

For example, if there are three hydroxyl groups attached to the benzene ring then the nomenclature of this phenol is considered to be benzene 1,2,3-diol. 

Example: The diagram below represents the structure of benzene 1, 2, 3 -diol.

  1. There are functional groups attached to the phenol molecule. Functional groups such as carbonyls, alcohols, carboxylic acids, or amines are known for changing the characteristics of the molecule. In the case of phenol, a functional group can also be attached.

Example:  An example of this can be ‘The Methyl Group’. 

  1. The nomenclature of the phenol structure above is 4-methyl phenol. Moreover, depending on where this functional group is attached, the labeling of the compound will differ. 

For example, if the functional group, methyl, was attached to ortho (attached to the adjacent carbon) then the name of the compound will be different from when it is attached to para (attached to the third carbon of the hydroxyl carbon). 

  1. Another common position where the functional group can be attached is meta (attached on the second carbon from the hydroxyl group). 

You should always remember the position of OH as it is given a high priority.

FAQ (Frequently Asked Questions)

1. What are phenols and their physical properties?

Phenols, at room temperature, occurs as a white solid or colorless liquids. Phenols and alcohols are similar except for the fact that phenols have stronger hydrogen bonds. Also, compared to alcohol, phenols are more soluble in water. Moreover, the boiling point for phenols is higher than that of alcohol. At room temperature, phenols can also be toxic and caustic. 

There are several physical properties of phenol that are important to be noted down. 

  • Due to the hydrogen bonding, phenols have a higher melting point and boiling point. 

  • Hydrogen bonding also leads to the higher solubility of phenols in water. 

  • Phenols can dissolve up to 9.3% of its solution in the water. 

  • Moreover, when a crystalline phenol is left in the atmosphere it picks up moisture from the air and forms liquid droplets. 

2. What are the uses of Phenols?

Nomenclature of phenols is considered as one of the major parts of organic chemistry. Phenol is a common industrial as well as a household product. Some common household uses of phenol are disinfectants, mouthwash, antiseptic. It is also sometimes used in cough syrups. With respect to industrial uses, phenols are commonly used to make plastics, explosives, medicines. It is also used in the dye industry. It is used as an antiseptic and is used in the production of nylon.