The E1cB mechanism is a less common elimination in which a base first removes a proton to give a carbanion, which is stabilised by a neighbouring group; this carbanion then expels the leaving group to form the carbon–carbon double bond (C=C). The name reflects that it is unimolecular (E1) in the conjugate-base (cB) intermediate. It matters where the carbanion is well stabilised and the leaving group is poor, so it operates in the reverse order of bond changes to the E1 mechanism.

E1cB 机理是一种较少见的消除,其中碱先夺取一个质子生成碳负离子,该碳负离子被相邻基团稳定;随后这个碳负离子排出离去基团,形成碳碳双键(C=C)。其名称表明它在共轭碱(cB)中间体上是单分子的(E1)。它在碳负离子被良好稳定且离去基团较差时起作用,因此其成键变化的顺序与 E1 机理相反。