Question

1) - In the following pairs of halogen compounds, which compound undergoes faster $S_{N}1$ reaction?


2) - In the following pairs of halogen compounds, which compouns undergoes faster $S_{N}1$ reaction?

Answer 1

1) - $S_{N}1$ reaction proceeds via formation of carbocation intermediate and formation of this intermediate is the rate determining step.

Therefore, greater is the stability of the carbocation, faster is the rate of $S_{N}1$ reaction.

Here, $2-\text{chloro-2-methylpropane}$ forms stable tertiary carbocation.

So, it readily undergoes $S_{N}1$ reaction while $3-\text{chloropentane}$ forms secondary carbocation which is less stable than tertiary carbocation, So, it does not easily undergo $S_{N}1$ reaction.

2) - $S_{N}1$ reaction proceeds via formation of carbocation.

Therefore, greater is the stability of the carbocation, faster is the rate of $S_{N}1$ reaction.

Here, 2-chloroheptane will form secondary carbocation (more stable) while 1-chlorohexane will form primary carbocation (less stable.)

So, 2-chloroheptane undergoes $S_{N}1$ faster then 1-chlorohexane.