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IUPAC names of Aromatic Compounds
Compounds containing one or more of benzene rings are known as aromatic family.
Out of these three, the last one is preferred because it represents the resonance hybrid of the first two structures. An aromatic compound may contain one or more side chains of carbon atoms. Substitution can take place either in the ring or in the side chain or both can be substituted.
If only one hydrogen atom of the benzene ring is replaced by another atom or group of atoms, a monovalent substituted derivative is formed. It can exist only in one form as all the six hydrogen atoms in benzene are equivalent. For example.
However, if two or more hydrogen atoms of the benzene ring are replaced by other atoms or group of atoms, these are indicated by Arabic numerals i.e., 1, 2, 3....... etc. In case of disubstituted compounds, it is also indicated by the following method.
(a) Ortho. The compound is termed as ortho if the two substituents are on the adjacent carbon atoms. In IUPAC system to indicate these positions are 1, 2.
(b) Meta. The compound is termed as meta if the two substituents are on alternate carbon atom. In IUPAC system to indicate these position are 1, 3.
(c) Para. The compound is termed as para if the two substituents are present on diagonally opposite carbon atoms. In IUPAC system to indicate these positions are 1, 4.
If the ring contains three or more substituents only Arabic numerals are used with alphabetical order. For example;
1. Nomenclature of aromatic compound.
The IUPAC and common names (given in brackets) of some important members are given below. However, if only one name is given, this indicates that the common name has been adopted by IUPAC system.
2. Nomenclature of aryl groups.
| Note : | (a) In case of tolyl group, no substitution is allowed. |
| (b) In case of phenyl group, unlimited substitution is allowed. |