Question

In the following pairs of halogen compounds, which compound undergoes faster SN¹
reaction?

Answer 1

SN1 reaction proceeds via the formation of carbocation. The alkyl halide (I) is 3° while (II)
is 2°. Therefore, (I) forms 3° carbocation while (II) forms 2° carbocation. Greater the stability of the carbocation, faster is the rate of SN¹ reaction. Since 3° carbocation is more stable than 2° carbocation. (I), i.e. 2−chloro-2-methylpropane, undergoes faster SN¹ reaction than (II) i.e., 3-chloropentane. (ii)

The alkyl halide (I) is 2° while (II) is 1°. 2° carbocation is more stable than 1° carbocation.
Therefore, (I), 2−chloroheptane, undergoes faster SN1 reaction than (II), 1chlorohexane.