Paragraph II
`S_N2` reaction is a bimolecular reaction which takes place by the formation of transition state. Velocity of the reaction depends on the concentration of the substrate as well as the nucleophile. The reaction is favoured by strong nucleophile, and in the presence of polar aprotic solvent, optically active halides give Walden inversion by `S_N2` mechanism. The presence of hetero group (atom) at `beta`-C atom,unsaturation at `beta`-C,and`(-overset(O)overset(||)(C)-)` group at `alpha` - C atom favour `S_N2` mechanism.
Allyl halides and benzyl halides give `S_N1` and `S_N2` reactions .Allyl halides also give `S_N2` mechanism. EWG at ortho- and para-positions in benzyl halides favours `S_N1` mechanism, whereas EDG favour `S_N2` mechanism.
Which of the following will give `S_N2` reaction?

Options

A. I and II
B. I and Ill
C. I, II and Ill
D. All

Answer

C

Explanation

`(I) to 1^@ RX,(II) to 1^@ RX,(III) to(-overset(O)overset(||)(C)-)` group at `alpha` -C atom,(IV) `rArr` Neopentyl halide (inert to `SN^2` reaction but undergoes carbocation rearrangement)