Question

For the following compounds, the correct statement(s) with respect to nucleophilic substitution reactions is(are)

• A. I and III follow $S_{N}1$ mechanism
• B. I and II follow $S_{N}2$ mechanism
• C. Compound IV undergoes inversion of configuration
• D. The order of reactivity for I, III and IV is: IV > I > III

Answer 1

Answer: (A), (B), (C)

The correct options are
A I and III follow $S_{N}1$ mechanism
B I and II follow $S_{N}2$ mechanism
C Compound IV undergoes inversion of configuration

Benzylic and $3^{\circ }$ halides both follow $S_{N}1$ mechanism.
Benzylic and $1^{\circ }$ halides both follow $S_{N}2$ mechanism.
Benzylic $2^{\circ }$ halides may follow both $S_{N}1$ and $S_{N}2$ mechanism
Benzylic $2^{\circ }$ halides can undergo inversion of configuration on $S_{N}2$ as it has chiral centre.

The order of reactivity should be IV > III > I if $S_{N}1$ is considered as the more stable the carbocation formed more reactive it is for $S_{N}1$ reaction. As per experimental data the order of stability of carbocation is $2^{\circ }$benzyl > $3^{\circ }$ alkyl > benzyl