Arrange the following set of compounds in order of their decreasing relative reactivity with an electrophile, E+
(a)Chlorobenzene, 2,4-dinitrochlorobenzene, p-nitrochlorobenzene
Electrophiles are reagents that participate in a reaction by accepting an electron pair in order to bond to nucleophiles.
The higher the electron density on a benzene ring, the more reactive is the compound towards an electrophile, E+ (Electrophilic reaction).
(a) The presence of an electron withdrawing group (i.e., NO2 -and Cl -) deactivates the aromatic ring by decreasing the electron density.
Since NO2 - group is more electron withdrawing (due to resonance effect) than the Cl - group (due to inductive effect), the decreasing order of reactivity is as follows: Chlorobenzene > p - nitrochlorobenzene > 2, 4 - dinitrochlorobenzene
While CH3− is an electron donating group, NO2− group is electron withdrawing. Hence, toluene will have the maximum electron density and is most easily attacked by E+.NO2− is an electron withdrawing group. Hence, when the number of NO2− substituents is greater, the order is as follows:
Toluene > p−CH3−C6H4−NO2,p−O2N−C6H4−NO2