Chemistry Reference
In-Depth Information
AROMATIC ORGANIC CHEMISTRY
S
B
UBSTITUTED
ENZENES
When three hydrogens are replaced by other substituents (trisubstitution),
the number of possible configurations is also three.
X
X
X
X
X
1
1
1
6
2
3
6
2
3
6
2
3
5
5
5
4
4
4
X
X
X
X
1,2,3-substitution
1,2,4-substitution
1,3,5-substitution
When different groups are present, they are numbered in ascending order
with the main substituent always in the 1-position.
CH
3
NO
2
2-nitro-4-chlorotoluene
Cl
With
trisubstitution
by the same or different substituents, the three
positional
isomers
shown above are possible. When the substituent groups are the same,
the positional numbers are given followed by the suffix “tri-.” For example,
if the three groups are chlorine, the first isomer above is named 1,2,3-
trichlorobenzene. The compound above with different substituents is named
as a derivative of the parent compound toluene (methylbenzene) where it is
understood that the methyl group is in the 1-position.
Substitution of four benzene hydrogens by the same group (tetrasubsti-
tution) also results in three positional isomers: 1,2,3,4-, 1,2,3,5-, and 1,2,4,5.
