The E1 and E2 elimination reactions exhibit distinct mechanisms for proton loss and have different substrate requirements.

E1 Elimination

E1 elimination follows a two-step mechanism. In the first step, the leaving group departs, resulting in the formation of a carbocation intermediate. Subsequently, a proton is lost from an adjacent carbon, leading to the creation of a double bond. E1 reactions typically require a tertiary or secondary substrate, a strong acid catalyst, and heat to facilitate the process. The rate of the reaction is influenced by the concentrations of both the substrate and the catalyst.

E2 Elimination

In contrast, E2 elimination is characterized by a one-step mechanism. During this process, the leaving group and a proton are eliminated simultaneously. The reaction proceeds through a single transition state, and the stereochemistry of the substrate remains intact. E2 reactions require a primary or secondary substrate, a strong base catalyst, and heat. Similar to E1, the rate of E2 reactions is also dependent on the concentrations of the substrate and the catalyst.

Key Differences

The primary distinction between E1 and E2 reactions lies in their mechanisms of proton loss. E1 reactions involve the formation of a carbocation intermediate, whereas E2 reactions occur in a single transition state. Furthermore, E1 reactions necessitate a tertiary or secondary substrate, while E2 reactions can proceed with a primary or secondary substrate. The choice of catalyst is another area of difference; E1 reactions require a strong acid, while E2 reactions call for a strong base.