Which one is most reactive towards S_(N) 1 reaction ?

1.	Which one is most reactive towards S_(N) 1 reaction ?
Answer» `C_(6)H_(5)C(CH_(3))(C_(6)H_(5))Br` `C_(6)H_(5)CH_(2)Br` `C_(6)H_(5)CH(C_(6)H_(5))Br` `C_(6)H_(5)CH(CH_(3))Br`. SOLUTION :For `S_(N)1` reactions, more stable is the carbocation, more reactive the alkyl or aryl HALIDE. The STABILITY of CARBOCATIONS increases in the order : `C_(6)H_(5) overset(+)CH_(2) lt C_(6)H_(5)overset(+)CHCH_(3) lt C_(6)H_(5)overset(+)CHC_(6)H_(5) lt C_(6)H_(6)overset(+)C(CH_(3))C_(6)H_(5)` Since (a) forms the most stable carbocation, it is most reactive. `underset("(Most reactive)")(C_(6)H_(5)-underset(CH_(3))underset(\|)overset(C_(6)H_(5))overset(\|)C-Br) overset(-Br^(-))to underset("(Most stable carbocation)")(C_(6)H_(5)-underset(CH_(3))underset(\|)overset(C_(6)H_(5))overset(\|)(C^(ox)))`

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