Page 158 - Pharm.Org.Chem-I 02-06-05-101

3- Polysubstituted compounds:

➢ If more than two groups are present on the benzene ring, the use of numbers is important to
indicate their positions.

➢ The benzene ring is numbered in order to give the substituents the lowest possible
numbers.

➢ If more than two substituents are present and they are different, they are listed in
alphabetical order.

➢ When a substituent is one that together with the benzene ring gives a new base name, that
substituent is assumed to be in position 1 and the new parent name is used.

1,2,3-Trichlorobenzene 1,2,4-Tribromobenzene 3,4-Dinitrobenzoic acid 3-Chloro-5-ethylbenzaldehyde
(not 1,3,4-tribromobenzene)

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Note that when a benzene ring is a substituent, it’s called a phenyl group.
A benzene ring with a methylene group is called benzyl group.

Phenyl group Benzyl group

Chloromethylbenzene Diphenyl ether Dibenzyl ether
(benzyl chloride)
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