# Regioselectivity for electrophilic aromatic substitution with multiple strongly electron withdrawing groups

At which position will electrophilic substitution on p-cyanonitrobenzene occur?

As both are -M groups, there are two possible sites of reaction, meta to each of the groups.
The answer is meta to $\ce{CN-}$. Why is this so? According to me it should be meta to $\ce{NO2}$, because $\ce{NO2}$ is the stronger -M group?

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• For such compound most eletrophilic subst. wouldn't work – Mithoron Aug 27 '15 at 12:15

As Mithoron suggests, the correct answer is probably "no reaction." There are no examples of electrophilic aromatic substitution of p-cyanonitrobenzene in SciFinder, by the introductory organic chemistry mechanism at least.

There is one report of halogenation (with N-halosuccinimide) of this compound with palladium catalysis. The cyano group serves as a directing group to place a halogen ortho to the cyano. Chlorination and bromination are both reported.

• Do you mean that there is no such reaction at all ? – mathemather Aug 28 '15 at 6:05
• @arutoregni using the typical conditions. For example, reaction of p-cyanonitrobenzene with bromine and iron tribromide has never been reported in the literature. Halogenation has been accomplished by a different mechanism, which is what is described in the answer. – jerepierre Aug 28 '15 at 15:54