Which of the following reaction`(s)` can be used for the preparation of alkyl halides?
(I) `CH_(3)CH_(2)OH+HCloverset(anhy.ZnCl_(2))(rarr)`
(II) `CH_(3)CH_(2)OH+HClrarr`
(III) `(CH_(3))_(3)COH+HClrarr`
(IV) `(CH_(3))_(2)CHOH+HCloverset(anhy.ZnCl_(2))(rarr)`

Options

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

Answer

A

Explanation

`ZnCl_(2)` is a lewis acid and interact with alcohol.
Carbocation is formed as intermediate in the `S_(N)^(1)` mechanism which these reaction undergoes.
In the absence of `ZnCl_(2)` formation of primary carbocation is difficult which is the case with (ii) while (i) undergoes reaction.
(iii) Tertiary carbocation casily formed due to the stability.
(iv) In the presence of `ZnCl_(2), 2^(@)` carbocation is formed from
`(CH_(3))_(2)-underset(H)underset(|)C-OH" i.e., "CH_(3)-overset(o+)CH-CH_(3)`