Question

Which one is most reactive towards $S_{N}1$ reaction?

• A. $C_6{H}_{5}CH\left(C_6{H}_5\right)Br$
• B. $C_6{H}_{5}C{H}_{2}Br$
• C. $C_6{H}_{5}CH\left(C{H}_3\right)Br$
• D. $C_6{H}_{5}C\left(C{H}_3\right)\left(C_6{H}_5\right)Br$

Answer 1

The correct option is D $C_6{H}_{5}C\left(C{H}_3\right)\left(C_6{H}_5\right)Br$

Order of $S_{N}1$ reactivity is the order of stability of carbocation formed as intermediate.
Carbocation formed by compound (b) is more stable than due to +R effect of two phenyl and +I effect of methyl group.
Order of stability of carbocations formed is

So, the order of the reactivity towards $S_{N}1$ reaction is,
B > A > C > D
Hence, option "B" is the correct answer.