Question

Question 13.22 Arrange the following set of compounds in order of their decreasing relative reactivity with an electrophile, E+

(a) Chlorobenzene, 2,4-dinitrochlorobenzene, p-nitrochlorobenzene

(b) Toluene, p-H3C–C6H4–NO2, p-O2N–C6H4–NO2.

Class XI Hydrocarbons Page 397

Answer 1

As you know, increases the number of electron withdrawing groups , reactivity of benzene nucleus towards Electrophile E+ decreases.

An electron releasing group activates the nucleus for the electrophilic substitution reaction while an electron withdrawing group deactivates it towards electrophile E+ .

Hence, it is clear that electrophile will attack easily in the presence of electron releasing group. And electrophilic will attack difficulty in the presence of electron withdrawing group.

Finally , we can say the order of reactivity towards Electrophile , E+ in order of their decreasing relative reactivity is

(a) chlorobenzene > p-nitrochlorobenzene > 2, 4 -dinitrochlorobenzene .

(b) Toluene > p-CH3-C6H4-NO2 >P-O2N-C6H4-NO2