The E1 and E2 reactions are two different types of elimination reactions in organic chemistry. They involve the removal of a leaving group and a hydrogen atom from adjacent carbon atoms, resulting in the formation of a double bond. The main difference between the two mechanisms lies in the number of steps involved and the nature of the transition state.E1 Reaction Mechanism:The E1 Elimination Unimolecular reaction is a two-step mechanism. Step 1: Formation of a carbocation intermediateIn the first step, the leaving group departs from the substrate, forming a carbocation intermediate. This step is slow and rate-determining, as it involves the breaking of a bond and the generation of a positively charged species.Step 2: Deprotonation of the carbocationIn the second step, a base abstracts a proton from a carbon atom adjacent to the carbocation, forming a double bond between the two carbon atoms. This step is relatively fast compared to the first step.E2 Reaction Mechanism:The E2 Elimination Bimolecular reaction is a one-step mechanism.In the E2 mechanism, the base abstracts a proton from a carbon atom adjacent to the leaving group, while simultaneously, the leaving group departs from the substrate. This concerted process results in the formation of a double bond between the two carbon atoms. The transition state involves partial bond formation and bond breaking, with no intermediate species formed.Examples of molecules undergoing E1 and E2 reactions:E1 Reaction:Tertiary alkyl halides, such as tert-butyl bromide t-BuBr , are good examples of molecules that undergo E1 reactions. Due to the high stability of the tertiary carbocation formed upon the departure of the leaving group, the E1 mechanism is favored.E2 Reaction:Primary alkyl halides, such as ethyl bromide CH3CH2Br , are more likely to undergo E2 reactions. In this case, the formation of a primary carbocation is less favorable, and the concerted E2 mechanism is preferred. Additionally, bulky bases, such as potassium tert-butoxide t-BuOK , can promote E2 reactions even in secondary and tertiary alkyl halides due to steric hindrance.