Based upon the following energy diagram, is this reaction an E1 or an E2 elimination
E1
E2
The Correct Answer and Explanation is :
The reaction depicted in the energy diagram you provided is an E1 elimination reaction. Here’s why:
- Energy Profile: The diagram shows a distinct two-step process characterized by two separate peaks in the energy profile. The first peak represents the formation of a carbocation intermediate, which is a hallmark of the E1 mechanism. This intermediate then undergoes a second step, leading to the formation of the final product, as indicated by the second, lower energy peak.
- Rate Determining Step (RDS): The initial peak in the diagram corresponds to the highest energy transition state, which is the rate-determining step of the reaction. In E1 eliminations, the RDS involves the loss of a leaving group to form a carbocation intermediate. The stability of this carbocation significantly influences the reaction rate, and its formation is often the slowest and most energy-demanding part of the process.
- Mechanistic Steps:
- Step 1: The leaving group departs, forming a carbocation. This step is unimolecular, involving only the substrate, hence the designation E1 (Elimination Unimolecular).
- Step 2: The base removes a proton from a carbon adjacent to the positively charged carbocation, leading to the formation of the double bond and the final elimination product. This step generally involves a lower activation energy as the formation of the double bond is energetically favorable.
- Absence of Bimolecular Interaction: The energy diagram does not suggest any concerted interaction between the base and the substrate in the rate-determining step. In an E2 mechanism, the base would simultaneously remove a hydrogen atom as the leaving group departs, which would typically be represented by a single concerted peak.
This analysis aligns with the characteristics of an E1 reaction, emphasizing the formation of a carbocation intermediate and the stepwise nature of the process. E2 reactions, on the other hand, would typically show a single concerted energy peak, reflecting the simultaneous removal of a proton by the base and the departure of the leaving group without the formation of a carbocation intermediate.