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

Options

A. `III gt IV gt II gt I`
B. `III gt II gt IV gt I`
C. `III gt II gt I gt IV`
D. `II gt III gt IV gt I`

Answer

C

Explanation

EDG favours `SN^(1)` reactivity with HBr. EWG retards `SN^(1)` reactivity with HBr. ED effect of `(-Me)` `(+R, -I)` is greater than (Me) group (+I and H.C.) So, reactivity of III gt II. In (IV), `(-OMe)` group is at m-position and exerts only -I effect and so reacitivity of (IV) is less than (I). So the reactivity order is: III gt II gt I gt IV.