Which of the following alcohols will yield the corresponding alkyl chloride on reaction with concentrated HCl at room temperature ?

Options

A. `CH_3CH_2-CH_2-OH`
B. `CH_3CH_2-underset(CH_3)underset(|)(CH)-OH`
C. `CH_3CH_2-overset(CH_3)overset(|)underset(CH_3)underset(|)(CH)-CH_2OH`
D. `CH_3CH_2-overset(CH_3)overset(|)underset(CH_3)underset(|)(C)-OH`

Answer

D

Explanation

When alcohols are treated with conc. HCl at room temperature than alkyl chloride is formed. This reaction follows `S_N^1` mechanism. `S_N^1` mechanism completes in two steps. In first step, a carbocation is formed and this carbocation is attacked by nucleophile in second step. The attack of nucleophile to the carbocation is possible only if the carbocation is stable. Compound present in option (d) will give tertiary carbocation in step I. Tertiary carbocation is most stable so it is further attacked by `Cl^(-)` nucleophile as follows
Step I
`CH_3-CH_2-overset(CH_3)overset(|)underset(CH_3)underset(|)(C)-OH rarr CH_3 -CH_2 - overset(CH_3)overset(|)underset(CH_3)underset(|)(C^(oplus))+overset(theta)(O)H`
Step II
`CH_3-CH_2-overset(CH_3)overset(|)underset(CH_3)underset(|)(C^(oplus))+Cl^(-) rarr H_3C-CH_2-overset(CH_3)overset(|)underset(CH_3)underset(|)(C)-Cl`