Question

The $S_{N}1$ reactivity of the following halides will be in the order:
(i) $(C{H}_3{)}_{3}CBr$
(ii) $(C_6{H}_5{)}_{2}CHBr$
(iii) $\left(C_6{H}_5{)}_{2}C\right(C{H}_3)Br$
(iv) $(C{H}_3{)}_{2}CHBr$
(v) $C_2{H}_{5}Br$

• A. $\left(v\right)>\left(iv\right)>\left(i\right)>\left(ii\right)>\left(iii\right)$
• B. $\left(ii\right)>\left(i\right)>\left(iii\right)>\left(v\right)>\left(iv\right)$
• C. $\left(i\right)>\left(iii\right)>\left(v\right)>\left(ii\right)>\left(iv\right)$
• D. $\left(iii\right)>\left(ii\right)>\left(i\right)>\left(iv\right)>\left(v\right)$

Answer 1

The correct option is D $\left(iii\right)>\left(ii\right)>\left(i\right)>\left(iv\right)>\left(v\right)$

$\text{Reactivity of}{S}_{N}1\text{reaction}\propto \text{Stability of carbocation}$

So the stability of carbocation follows the order:
$\underset{\left(iii\right)}{(C_6{H}_5{)}_2}\stackrel{\oplus }{C}\left(C{H}_3\right)>\underset{\left(ii\right)}{(C_6{H}_5{)}_2\stackrel{\oplus }{C}H}>\underset{\left(i\right)}{(C{H}_3{)}_3\stackrel{\oplus }{C}}>\underset{\left(iv\right)}{(C{H}_3{)}_2}\stackrel{\oplus }{C}H>\underset{\left(v\right)}{C{H}_3}\stackrel{\oplus }{C}{H}_2$