Basic IUPAC Organic Nomenclature

Polysubstituted benzenes

• When there are two (or more) substituents, the relative position of the subsituents must be defined. 
  
• Numerical locants are used to specify the locations if there are three (or more substituents).
  
• The principal functional group is defined to be at C1.
• In cases where the root can be defined using common aromatic names this is typically used.
• The remaining substituents are listed alphabetically.

Principle functional group is the methylbenzene therefore root = toluene There is a bromine substituent therefore bromo There is a chlorine substituent therefore chloro Numbering from the -CH3 (priority group at C1) gives the substituents the locants = 2 and 4 2-bromo-4-chlorotoluene
Principle functional group is the aromatic alcohol therefore = phenol There are two C1 substituents therefore dimethyl Numbering from the -OH (priority group at C1) gives the substituent the locant = 3,5 3,5-dimethylphenol
Principle functional group is the aromatic amine therefore = aniline There is a C1 substituent therefore methyl There is a C2 substituent therefore ethyl Numbering from the -NH2 (priority group at C1) gives the substituents the locants = 2 and 3 2-ethyl-3-methylaniline

©Dr. Ian Hunt, Department of Chemistry