Regioselectivity for electrophilic aromatic substitution with multiple strongly electron withdrawing groups


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




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.


Reference: [Palladium-Catalyzed Highly Selective ortho-Halogenation (I, Br, Cl) of Arylnitriles via sp2 C–H Bond Activation Using Cyano as Directing Group](http://pubs.acs.org/doi/abs/10.1021/jo302765g)


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