Which one of the following is more reactive towards `S_N2` reaction?

Options

A. `CH_(2)=CH-CH_(2)-Cl`
B. `Ph-CH_(2)-Cl`
C.
D. `Ph-underset(O)underset(||)C-CH_(2)-Cl`

Answer

D

Explanation

Here you see a typical `S_(N^2)` reaction of.allyl bromide. We have draw the transition state for this reaction. This is not because we want to encourage you to do this for all `S_N`reactions but so that we can explain the role of the allyl system. Allyl compounds react rapidly by `S_(N^2)` mechanism because the double bond can stabilize the transitions state by conjugate.

The benzyl group acts in much the same way using the it system ofthe benzene ring for conjugation with thep-orbital in the transition state.
`S_(N^2)` reaction ofbenzyl bromide

Relative rates of `S_(N^2)` reaction ofalkyl chlorides with the iodide ion