Give the decreasing order of the reaction rates of the following benzyl with HBr.
(I)

Options

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

Answer

A

Explanation

The positive charge that develops on benzylic C in this `SN^(1)` reaction is most effectively delocalised by )Ome) group (+R and -I). The `(p-NO_(2))` group withdraw `bar e` density form the ring by -I and -R. `(p-CI)` groupwithdraw `bar e`'s form the ring by -I only. More EDG (e.g. -OMe) stabilises positive charge on the benzyl C atom, whereas EDG (e.g., `-NO_(2),-CI`) destabilises the positive charge. Hence, the reactivity otder is: I gt II gt III gt IV.