Nomenclature of Aromatic Compounds

Aromatic compounds

Organic compounds containing one or more benzene rings and their functionalized derivatives are called aromatic compounds.

Note : There are ,however, examples of aromatic compounds which do not contain a benzene ring but instead contain other highly unsaturated ring.

Benzene can be represented as either of the following ways :

Benzene

For IUPAC nomenclature of aromatic compounds, the substituent is placed as prefix to the word benzene.

Methylbenzene (Toluene)

IUPAC Nomenclature of aromatic compounds example : Toluene

Nitrobenzene

Many substituted benzene compounds are popular by their common names. Some of them are given below :

Example 1 : Methylbenzene

Common name is Toluene

Example 2 : Methoxybenzene

IUPAC Nomenclature of aromatic compounds example : Anisole

Common name is Anisole

Example 3 : Aminobenzene

IUPAC Nomenclature of aromatic compounds example : Aniline

Common name is Aniline

Example 4 : Hydroxybenzene

IUPAC Nomenclature of aromatic compounds example : Phenol

Common name is Phenol

Disubstituted benzene ring : If a benzene ring is disubstituted i.e. contains two substituents, the position of the substituents is defined by numbering the carbon atoms in such a way that the substituents are located at the lowest number possible.

Example

1,2-Dichlorobenzene

ortho (o), meta (m), para (p)

In the trivial system of nomenclature, the terms ortho, meta and para are used as prefixes to indicate the relative positions of the substituents present.

ortho (o)

ortho is used to indicate that the relative position between the substituents present is 1,2-. o can alternatively be used in place of ortho. For example :

ortho-dibromobenzene = o-dibromobenzene

Example : o-dichlorobenzene

IUPAC Nomenclature of aromatic compounds example : ortho dichlorobenzene

IUPAC name : 1,2-Dichlorobenzene

meta (m)

meta is used to indicate that the relative position between the substituents present is 1,3-. m can alternatively be used to represent meta.

Example : m-dichlorobenzene

IUPAC Nomenclature of aromatic compounds example : meta dichlorobenzene

IUPAC name : 1,3-Dichlorobenzene

para (p)

para is used to indicate that the relative position between the substituents present is 1,4-. p can alternatively be used to represent para.

Example : p-dichlorobenzene

IUPAC Nomenclature of aromatic compounds example : para dichlorobenzene

IUPAC name : 1,4-Dichlorobenzene

Note : ortho, meta and para cannot be used for tri or higher substituted benzene compounds.

In some cases, common name of benzene derivatives is taken as the base compound. Substituent of the base compound is assigned number 1 and then the numbering is done in such a way that the next substituent gets the lowest number.

Example : 4-Ethyl-2-methylphenol

Example : 2-Chloro-4-methylanisole

When a benzene ring is attached to a side chain which contains a functional group, the benzene ring is considered as a substituent. The name of benzene as a substituent is phenyl.

Example : 3-Phenylpropanoic acid

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