AIPMT 2010 Physics and Chemistry Paper

Key Idea: SN1 reaction involves the formation of carbocation intermediate. More the stability of carbocation, more is the reactivity of alkyl\/aryl haldies towards SN1 reaction.
The intermediate carbocations formed by given haldies are as :
(1) C6H5‌CH(C6H5)‌Br→(C6H5)2‌

+

C

H+Br−
(2) C6H5‌CH(CH3)‌Br→C6H5

+

C

H(CH3)+Br−
(3) C6H5C(CH3)(C6H5)‌Br→(C6H5)2‌

+

C

(CH3)+Br−
(4) C6H5CH2‌Br→C6H5

+

CH

2+Br−
The order of stability of these carbocations is as
Thus, C6H5C(CH3)(CH3)(C6H5)‌Br is most reactive towards SN1 reaction.