Question

In the following pair of halogen compounds, which compound undergoes \( S_N1 \) reaction faster and why?

Hint:

Remember, in \( S_N1 \) reactions, the stability of the carbocation intermediate is crucial. More substituted carbocations are generally more stable and form faster, leading to a quicker overall reaction.

Answer 1

Step 1: Understanding the \( S_N1 \) Mechanism.
The \( S_N1 \) reaction proceeds via a two-step mechanism:
1. Formation of a carbocation (rate-determining step).
2. Nucleophilic attack on the carbocation.
The rate of the \( S_N1 \) reaction depends on the stability of the carbocation. Tertiary carbocations are more stable due to greater alkyl group substitution which provides better electron donation through hyperconjugation and inductive effects. This stability accelerates the formation of the carbocation, thus enhancing the reaction rate.
Given two halogen compounds, the one with the tertiary halogenated carbon (i.e., more substituted carbon) will form a more stable carbocation and thus undergoes the \( S_N1 \) reaction faster.