CHAPTER VIAROMATIC NITRO COMPOUNDS
REACTIVITY OF THE NITRO GROUP
AROMATIC nitro compounds which are of course tertiary, form a separate group
of compounds, differing from the aliphatic nitro derivatives in many respects.
For this reason they deserve special attention.
The attachment of nitro groups to the aromatic ring affects their reactivity.
For example, nitro groups in ortho or para position in relation to each other
are rather reactive, and one of them can be substituted relatively easily. Only
the nitro groups in the meta position to each other are stable. Thus, one of the
nitro groups in the unsymmetrical trinitrotoluenes (isomers of TNT) can readily
be substituted. This is a consequence of the substitution rule, that the nitro group
directs a new entrant group towards meta position. If in an aromatic compound
two nitro groups, i.e. meta-orienting groups, are in a different - ortho or para
position in relation to each other, the system must be unstable.
A nitro group may also become mobile under the influence of a large number
of substituents in the same ring. The following reaction was observed by Körner and
Contardi [l] as early as 1914:
(1)Peters, Rowe and Stead [2] observed a similar reaction, accompanied by hydro-
lysis as a side-reaction:
5% yield