Give the decreasing order of reactivity of the following compounds with HBr. (I) (II) (III) (IV)

Step-by-step solution

Electron Releasing Group favours S N 1 reactivity with HBr . EWG retards S N 1 reactivity with HBr . ERG effect of - O M e ( + R , - I ) is greater than ( M e ) group + I a n d H . C . . So, reactivity of I I I > I I . In I V , - O M e group is at m-position and exerts only - I effect and so reactivity of I V is less than I . So the reactivity order is: I I I > I I > I > I V