Which of the following statements about an $E1$ mechanism is NOT true?

• A. The rate of the reaction depends only on the concentration of the substrate.
• B. Rearrangement of the carbocation intermediate can occur.
• C. A carbocation intermediate is formed during the reaction.
• D. The leaving group departs after the base removes a proton.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the E1 mechanism involves two main steps: first, the leaving group departs forming a carbocation intermediate; second, a base removes a proton from a β-carbon to form the alkene.
2. Step 2: Recognize that the rate-determining step in an E1 reaction is the formation of the carbocation, so the rate depends only on the concentration of the substrate, not the base.
3. Step 3: Note that because a carbocation intermediate is formed, rearrangements (such as hydride or alkyl shifts) can occur to form a more stable carbocation.
4. Step 4: Analyze the statement 'The leaving group departs after the base removes a proton' and compare it to the actual mechanism where the leaving group departs first, before the proton is removed.
5. Step 5: Conclude that the incorrect statement is the one claiming the leaving group departs after the base removes a proton, as this contradicts the stepwise nature of the E1 mechanism.