The increasing order of reactivity of the following halides for S_(N)1 reaction is- underset((I))(CH_(3)underset(Cl)underset(|)(C)HCH_(2)CH_(3)), underset((II))(CH_(3)CH_(2)CH_(2)Cl) underset((III))(p-H_(3)CO-C_(6)H_(4)-CH_(2)Cl)

The increasing order of reactivity of the following halides for S_(N)1

1.	The increasing order of reactivity of the following halides for S_(N)1 reaction is- underset((I))(CH_(3)underset(Cl)underset(\|)(C)HCH_(2)CH_(3)), underset((II))(CH_(3)CH_(2)CH_(2)Cl) underset((III))(p-H_(3)CO-C_(6)H_(4)-CH_(2)Cl)
Answer» (III) lt (II) lt(I) (II) lt (I) lt (III) (I) lt (III) lt (II) (II) lt (III) lt (I) Solution : Benzylic carbocation is stabilised by resonance with the `pi`-electorns of benzene RING and the EXTENT of resonance stabilisation is further INCREASED by the presence of electron donating -`OCH_(3)` group in the para-position of benzene ring. We know `2^(@)` carbocation is more stable than `1^(@)` carbocation. so the order of stability of the carbocations is: benzylic carbocation > `2^(@)` carbocation > `1^(@)` carbocation. The feasibility of `S_(N)1` reaction is DIRECTLY proportional to the stability of carbocation. Hence, the increasing order of REACTIVITY of the given halides for `S_(N)1` reaction is (II) < (I) < (III).