`SN` reaction is given by these compounds, which have a nuclophilic group and a good leaving `EWG`. It should be stable after leaving with bonding pair of `overline(e)'s` and it should have high polarisability.
Nucliphilic aliphatic substituion reaction is mainly of two types `SN^(-1)` and `SN^(2). SN^(-1)` mechanism is a two step process. Reaction velocity of `SN^(-1)` depends only on the concentration of the subtrate. It proceeds via the formation of carbocation, optically active substrate gives `(o+)` and `(o-)` froms of the product.
In most of the cases, the product usually consists of `5-20%` inverted and `(95-80%)` racemised species. The more stable is the carbocation, the greater is the propotion of racemission. In solvolysis reaction, the more nucleophillic is the solvent, the greater is the proportion of inversion.
Which of the following gives `SN^(1)` reaction?

Select the correct answer.

Options

A. `(I),(II)` and `(III)`
B. `(I)` and `(II)`
C. `(II),(III)`, and `(IV)`
D. `(I),(III)`, and `(IV)`

Answer

`b`

Explanation

Stabiliy of carbocation: Benzyl `C^(o+) gt Allyl C^(o+) gt 3^(@)C^(o+) (I) gt (II)`
`(IV)` gives `Me_(3) - overset(o+)(C)H_(2)` (neopntyt, `C^(o+)`) (sterically hindered). It undergoes neither `SN^(-1)` nor ``SN^(2)`.