Most of the aromatics have an aroma, thus the name “aromatic.”
The C 6 H 5 group is a substituent called phenyl. This is the benzene structure
with one hydrogen missing. If the phenyl substituent adds a methyl group, the
compound is called toluene or methyl benzene.
Two other members of the benzene series and their structures:The IUPAC system of naming benzene derivatives, as with chain compounds,
involves numbering the carbon atoms in the ring in order to pinpoint the locations
of the side chains. However, if only two groups are substituted in the benzene
ring, the compound formed will be a benzene derivative having three possible
isomeric forms. In such cases, the prefixes ortho-, meta-, and para-, abbreviated
as o-, m-, and p-, may be used to name the isomers. In the ortho- structure, the two
substituted groups are located on adjacent carbon atoms. In the meta- structure,
they are separated by one carbon atom. In the para- structure, they are separated
by two carbon atoms.