Chemistry Reference
In-Depth Information
AROMATIC ORGANIC CHEMISTRY
S
B
UBSTITUTED
ENZENES
When two hydrogens on a benzene ring are replaced by other elements
(disubstitution), there are three possible configurations, as shown here, where
X
=
a substituent group, either the same or different.
X
X
X
X
1
1
1
6
2
3
6
2
3
6
2
3
5
5
5
4
4
4
X
X
1,2- or “
ortho
-”
1,3- or “
meta
-”
1,4- or “
para
-”
substitution
substitution
substitution
The position of substituents on the ring and their relation to each other
corresponds to the number of the carbon to which they are attached.
Substitution of two or more hydrogens in benzene results in “positional
isomerism.” Positional isomers have the same formula, but different physical
and chemical properties. In disubstituted benzene, three positional isomers are
possible, as shown above. If the
are the same or different, one is
always listed in the 1-position. If the substituents are different, they are listed
alphabetically.
substituents
