Question

Which of the following compound will undergo $S_{N}1$ reaction?

• A.
• B.
• C.
• D. All the above

Answer 1

The correct option is B

$S_{N}1$ reaction goes by formation of carbocation intermediate. Thus compound forming stable carbocation will undergo $S_{N}1$ reaction.
Compound (a) is a vinyl bromide. Here, the formed carbocation will have positive charge on $sp$ carbon which is highly electronegative compare to $s{p}^3$. Thus, it is not a stable carbocation so it won't undergo $S_{N}1$ reaction.

Compound (b) forms allyl carbocation which is stabilised by delocalisation of $\pi$ bond. Hence, it undergo $S_{N}1$ reaction.
Compound (c) forms aryl cation which is too unstable to form due to positive charge on sp carbon. Hence, it does not give $S_{N}1$ reaction.