Consider the $E1$ reaction of the tertiary halide shown. Which of the following statements best describes the rate-determining step of this reaction?

• A. The rate-determining step is the deprotonation of the $\beta$ hydrogen by the base.
• B. The rate-determining step is the nucleophilic attack on the carbocation intermediate.
• C. The rate-determining step is the simultaneous removal of the leaving group and a proton in a concerted process.
• D. The rate-determining step is the loss of the leaving group to form a carbocation intermediate.

Answer: (D)

Verified step by step guidance

1. Identify the type of reaction: An E1 reaction involves two main steps—a slow, rate-determining step where the leaving group departs forming a carbocation intermediate, followed by a fast deprotonation step.
2. Understand the rate-determining step: In E1 mechanisms, the rate depends only on the concentration of the substrate because the first step (loss of the leaving group) is the slowest and controls the reaction rate.
3. Analyze the options: The deprotonation of the β-hydrogen by the base is a fast step that occurs after the carbocation forms, so it is not rate-determining.
4. Recognize that nucleophilic attack is not involved in E1 elimination; instead, the base removes a proton after carbocation formation, so nucleophilic attack on the carbocation is not the rate-determining step.
5. Conclude that the rate-determining step is the formation of the carbocation intermediate by loss of the leaving group, which is a unimolecular process characteristic of E1 reactions.