Question

Consider the following bromides:

The correct order of $S_{N}1$reactivity is

• A. $A > B > C$
• B. $B > C > A$
• C. $B > A > C$
• D. $C > B > A$

Answer 1

Answer: (B)

$B > C > A$

Answer 2

$S_{N}1$reaction rate depends upon the stability of the carbocation as carbocation formation is the rate determining step. Compound (2), forks a $20{^\circ}$allylic carbocation which is the most stable, the next stable carbocation is formed form (3), it is a $2{^\circ}$carbocation, (1) foms the least stable $1{^\circ}$carbocation, the order of reactivity is thus.