Naming aromatic compounds

Aromatic compounds with one substituent group are monosubstituted. 

The benzene ring is often considered to be the parent chain 

Alkyl groups (CH3, C2H5) and halogens (F, Cl, Br, I)  and nitro groups (NO2) are all considered prefixes to benzene. 

nitrobenzene:

When a benzene ring is attached to an alkyl chain with a functional group or to an alkyl chain with seven or more carbon atoms, benzene is considered a substituent. Instead of benzene the prefix phenyl is used in the name. 

phenylethanone

Some compounds may contain more than one substituent on the benzene ring for example disubstituted compounds have two substituent groups. The ring is now numbered just like a carbon cahin starting with one of the substituent groups. The substituent groups are listed in alphabetical order using smallest numbers possible.