Unimolecular Conjugate Base Elimination Reaction
E1cB Mechanism takes place in two steps. First step involves a fast and reversible removal of proton from the β-carbon with the formation of a carbanion which then loses the leaving group (LG) in the second slow rate determinig step and forms alkene. The overall rate of reaction is dependent on the concentration of the conjugate base of the substrate (carbanion). Hence, this mechanism has been designed as E1cB (Elimination, Unimolecular from conjugate base). E1cB mechanism follows 1st order kinetics.
Rate ∝ [Substrate]
Rate = k [Substrate]
Generally, E1cB mechanism occurs when there is resonance withdrawing group between the leaving group (LG) and the hydrogen. The role of electron withdrawing group is to stabilize the carbanion formed after removal of proton from β-carbon. Other condition for E1cB mechanism is acidic hydrogen on β-carbon and poor leaving group on α-carbon atom.
Also read E1 Reaction | E2 Reaction | Ei Reaction
